Chickadees Whistling in the Wind

Another find from this last weekend:

Black-capped Chickadee (Poecile atricapilla), Starved Rock State Park,
La Salle Co, IL 1/26/2014

This little fellow is a Black-capped Chickadee, a favorite of mine. They're adaptable, fairly tame, very vocal,...

Very vocal indeed. They have a fairly wide repertoire of call types. (Not like mimics, these are different calls for different situations.)

The call that gave them their name includes several high see notes, a couple of quick lower notes and a series of low, burry dee notes. They don't always use all of them, and the number of see and dee notes varies. What they do use, they always use in order, though. This set of calls is used in quite a few contexts, and the variation in the number of each note appears to actually convey information(1).
One context that these notes may be used in (especially the dee notes) is mobbing of predators, owls and small hawks in particular. Vervet Monkeys (Chlorocebus pygerythrus) and Prairie Dogs (Cynomys spp.) have different calls for different predator types (2,3), and apparently chickadees do something similar, encoding information about the size and potential threat posed by a predator in their calls (4).

One of the remarkable things about this species' vocal behavior is the geographic variation that is seen. Their well-known 'fee-bee' song is remarkably uniform across the entire continent, although they vary the pitch to add some variety (5). But another vocalization, typically termed the 'gargle', changes across a few miles (6). There is some evidence that isolated populations diverge faster than other populations (7), as might be expected. This suggests that there is a considerable degree of contact across the entire continent, given the speeds at which other species appear to develop geographic dialects. But that doesn't explain how local geographic variation in the gargle call occurs, and is a rather odd thing to contemplate for a small bird that doesn't migrate.

Quite a bit of work has been done on these little guys, and their behavior can still mystify us. If you hear someone complaining about how science removes the mystery from life, just remember these little guys.

(1) Freeberg, T. M., & Lucas, J. R. (2002). Receivers respond differently to chick-a-dee calls varying in note composition in Carolina chickadees,< i> Poecile carolinensis</i>. Animal Behaviour, 63(5), 837-845.

 

(2) Seyfarth, R. M., Cheney, D. L., & Marler, P. (1980). Vervet monkey alarm calls: semantic communication in a free-ranging primate. Animal Behaviour, 28(4), 1070-1094.

 

(3) Slobodchikoff, C. N., Kiriazis, J., Fischer, C., & Creef, E. (1991). Semantic information distinguishing individual predators in the alarm calls of Gunnison's prairie dogs. Animal Behaviour, 42(5), 713-719.

 

(4) Templeton, C. N., Greene, E., & Davis, K. (2005). Allometry of alarm calls: black-capped chickadees encode information about predator size. Science, 308(5730), 1934-1937.

 

(5) Kroodsma, D. E., Byers, B. E., Halkin, S. L., Hill, C., Minis, D., Bolsinger, J. R., ... & Wilda, K. (1999). Geographic variation in black-capped chickadee songs and singing behavior. The Auk, 387-402.

 

(6) Miyasato, L. E., & Baker, M. C. (1999). Black-capped chickadee call dialects along a continuous habitat corridor. Animal behaviour, 57(6), 1311-1318.

 

(7) Gammon, D. E., Baker, M. C., & Tipton, J. R. (2005). Cultural divergence within novel song in the black-capped chickadee (Poecile atricapillus). The Auk, 122(3), 853-871.

East meets West meets Southwest

Photographing birds at feeders can provide some great opportunities:

Red-bellied Woodpecker (Melanerpes carolinus), Starved Rock State Park,
La Salle Co, IL 1/26/2014



This is a female Red-bellied Woodpecker.

Red-bellied Woodpeckers are closely related to two other North American species, the Gila Woodpecker of the desert southwest and the Golden-fronted Woodpecker, found mostly in Texas and south into Mexico. Where these species meet they will occasionally hybridize, but since it's so rare, we call them separate species.

Here's a Dark-eyed Junco:

Slate-colored Junco (Junco hyemalis), Starved Rock State Park,
La Salle Co, IL 1/26/2014

And here's another one:



Pink-sided Junco (J. hyemalis), Bear Creek Nature Center
El Paso Co, CO 12/21/2011

And another one:

Oregon Junco (J. hyemalis), Bear Creek Nature Center,
El Paso Co, CO 12/28/2011

And yet another Dark-eyed Junco:


Gray-headed Junco (J. hyemalis), Bear Creek Nature Center,
El Paso Co, CO 12/21/2011

Dark-eyed Juncos show extensive, rather complex geographic variation, with 12 recognized subspecies in 6 distinctive groups. Where they meet, there is extensive hybridization, so we call them the same species.

And finally, here's a Northern Flicker:



Yellow-shafted Flicker (Colaptes auratus), Illinois Beach State Park,
Lake Co, IL 9/30/2013

And here's another:

Red-shafted Flicker (C. auratus), Colorado Springs,

El Paso Co, CO 12/21/2005

 

These guys occur in 5 subspecies that segregate nicely into two groups - the eastern Yellow-shafted and the western Red-shafted. There is extensive hybridization on the Great Plains, and genes from each group appear to have penetrated all the way to the opposite coasts.

 

At one time or another, each of these critters has been considered a "good" species. In some cases the subsequent changes were due to additional information, but in most cases they were due to changing concepts of what constitutes a species. Prior to the 20th century, morphology was the primary criterion -- do these two birds look different enough? After Ernst Mayr proposed his biological species concept (1), the presence of a hybrid zone was considered evidence that two forms were the same species. Today, many observers look for genetic distances (2), or for assortative mating preferences.

This sort of shift in our concepts to some degree reflects our increasing understanding of biology*, but it also reflects the difficulties inherent in the very question, "What's a species?" Clearly, in the case of the Red-bellied Woodpecker, the different forms are good species, but equally clearly they split off from one common ancestor relatively recently (as evolutionary biologists define recent, anyways). That splitting is usually a messy process, which can take quite a long time. This means that we if we look around, we are likely to see populations of organisms that are in every stage of this process, from barely differentiated (Northern Flickers) through partially split (Juncos, Red-naped and Red-breasted Sapsuckers perhaps), through good, well-behaved species (Eastern and Western Meadowlarks). Trying to define where in the process we call them good species is kind of like deciding when a person becomes an adult -- it depends upon what criteria we're using for adulthood. As our knowledge of birds increases, the criteria we deem important in delineating species is likely to change (3), and we can expect to see the field guides change periodically for the foreseeable future.

*And not, contrary to the opinions of some birders, a conspiracy to sell more field guides as they are updated to reflect the changes.

(1) Mayr, E. 1942. Systematics and the origin of species. Columbia Univer- sity Press, New York.

 

(2) Kerr, K. C., Stoeckle, M. Y., Dove, C. J., Weigt, L. A., Francis, C. M., & Hebert, P. D. (2007). Comprehensive DNA barcode coverage of North American birds. Molecular Ecology Notes, 7(4), 535-543.

 

(3) De Queiroz, K. (2007). Species concepts and species delimitation. Systematic Biology, 56(6), 879-886.

Rough-legs at Rollins

Here's a nice find from Rollins Savanna Forest Preserve today:

Adult male Rough-legged Hawk (Buteo lagopus), Rollins Savanna Forest Preserve,
Lake Co, IL 1/29/2014

This is a Rough-legged Hawk (Buteo lagopus). They breed on the Arctic tundra of Alaska and Canada as well as Eurasia. This year has seen a major invasion in the middle of the continent, similar to the eastern Snowy Owls.

This guy is a light morph adult male. Rough-legged Hawks show a good deal of plumage polymorphism, with light, intermediate, and at least two dark morphs in addition to age and sex-related variation in each morph. Here's a dark morph bird for comparison:

Dark Rough-legged Hawk, Illinois Beach State Park, Lake Co, IL 10/29/2012

This is normal variation, in contrast with albinism or leucism, which arise from an inability to make or lay down pigments for some reason, as seen in this Red-tailed Hawk (B. jamaicensis):

Leucistic Red-tailed Hawk (Buteo jamaicensis), Illinois Beach State Park,
Lake Co, IL 11/9/2013

Buteos in general seem quite prone to this sort of polymorphism, with 15 of 29 species listed in Ferguson-Lees and Christie's Raptors of the World showing distinct dark and light morphs (1). Here in North America, there is a fairly consistent pattern associated with this -- eastern birds (except the largely neotropical Short-tailed Hawk (B. brachyurus)) don't show a dark morph. Of our western buteos, only Red-shouldered Hawk (B. lineatus) in California and Gray Hawk (B. nitidus) don't show one.  White-tailed Hawks (B. albocaudatus) in Texas do not have a dark morph, although there is a range of variation in juveniles, but the same species in South America does. Red-tailed Hawks in the east don't show a dark morph, even though dark Red-tails are rather common in the west. Even Broad-winged Hawks (B. platypterus) have a dark morph in the west -- they breed at the western edge of the species' range, at the eastern edge of the Canadian Rockies in northern Alberta. Swainson's Hawks (B. swainsoni) nesting on the central and eastern Great Plains are all light morph, whereas farther west we see dark morphs appearing.

This pattern is a puzzle. There is a general rule that populations in humid climates tend to be darker than those in arid climates, known as Gloger's Rule, but the dark morphs in the west tend to be in drier environments than the strictly light morphs in the east. The varied topography in the west does suggest a greater variety of potential habitats, but I've never seen the morphs correlated to habitats, and they don't appear to segregate that way in my experience.

There is also one species that bucks the trend: Rough-legged Hawks. Dark morphs in this species are most common in humid areas in Alaska and eastern Canada, which fits Gloger's Rule, but for some reason they are unknown in Eurasia. (2)

Polymorphism in buteos has been argued to be adaptive because prey species might not recognize those dark birds as predators. Roulin & Wink (3) found that polymorphic species preyed more often on mammals than non-polymorphic species, but Galeotti & Rubolini (4) found no evidence for this. They argued instead that species that lived in variable habitats are undergoing disruptive selection, which can maintain genetic variation in a population.  So we're still not sure why these polymorphisms are present in the first place, and what produces the geographic pattern we see is a mystery: Is there some sort of adaptive significance to dark plumage that we're missing? Is there some sort of sexual selection going on? Are we seeing the result of differing history of the two regions? Perhaps eastern populations underwent a population bottleneck during the last glacial maximum, and the dark morph alleles disappeared from their populations?

Biologists have learned some amazing things about the critters we share the world with, but if a bunch of big, highly visible charismatic birds can still hold on to such secrets, we clearly aren't going to run out of questions to ask anytime soon.

(1) Ferguson-Lees, James & David A. Christie. (2005). Raptors of the World. Princeton: Princeton University Press.

(2) Wheeler, Brian K. (2003). Raptors of Eastern North America. Princeton: Princeton University Press.

(3) Roulin, A., & Wink, M. (2004). Predator‐prey relationships and the evolution of colour polymorphism: a comparative analysis in diurnal raptors. Biological Journal of the Linnean Society, 81(4), 565-578.

(4) Galeotti, P., & Rubolini, D. (2004). The niche variation hypothesis and the evolution of colour polymorphism in birds: a comparative study of owls, nightjars and raptors. Biological Journal of the Linnean Society, 82(2), 237-248.

Pines on the Rocks

Starved Rock State Park really doesn't look like it belongs in Illinois:

White Pines (Pinus strobilus) in French Canyon, Starved Rock State Park, La Salle Co, IL 1/26/2014

The green trees on those cliffs are Eastern White Pines (Pinus strobilus) and this is pretty far south for them. In the Midwest, you only find small patches of them south of Wisconsin and Michigan, whereas they're a major component of the North Woods in the upper Great Lakes. (They do occur well south in the Appalachians, but at higher altitudes than you can find in Illinois.)

The same sort of pattern exists for this tree:

Northern White Cedar (Thuja occidentalis),
Starved Rock State Park, La Salle Co, IL  1/26/2014

Only in spades -- even in the Appalachians, White Cedar* (Thuja occidentalis) only occurs in small patches south of New York. In places where they're common, they're found in wet lowland areas, but they will also grow on cliffs like you find in Starved Rock.

Why do we see these little outlier populations? One possible explanation is that they were planted by people, but it's hard to see why people would be planting White Cedars here. Some sort of odd dispersal event is also possible, but it seems unlikely that two different species would show up together in the same location. That leaves a scenario wherein these plants are relicts of an earlier, more southerly distribution.

Since we know from geological and paleoecological evidence that the upper Midwest was glaciated 11,000 years ago and pines and even spruces reached south-central Illinois during glacial periods (1), this relict scenario has a lot going for it.

But why here and not elsewhere? Those cliffs visible in the first shot and more clearly here give the

answers. First, the little canyons that these cliffs form all face north, which means that they are short on sunlight and therefore stay cooler than surrounding areas. Second, with the rock so close to the surface, soil is at a premium, and therefore many plants can't survive there. Those plants that can have a spot all to themselves.

Both species mentioned above are quite capable of growing in rocky soils, although they both grow better in deeper soil. White Cedar especially is known for growing on cliffs, and when it does so, it grows very slowly and can reach ages of 1000 years. This sort of longevity increases the chances that a population can persist in small pockets for us to find, making the relict population scenario even more likely.

These little relict populations are an important reminder that the natural world isn't static. Communities are always changing, and species distributions grow and shrink for all sorts of reasons. Those changes do accelerate greatly when modern technology gets involved, of course. Still, this concept of an ever-shifting natural world produces an interesting dilemma for conservationists. We want to protect ecosystems that, often enough, have gone from common to very rare through human activity. (Think tallgrass prairie.) Frequently there is so little left that the loss of even one site is truly problematic. But the systems themselves are built on change, and eliminating that change means interrupting some of the very processes that we're interested in preserving.

The pines and cedars at Starved Rock are holdouts from a time when their compatriots held sway over vast areas of the southern Midwest. Those other trees disappeared with the slow warm-up that happened as the Wisconsin glaciers retreated -- a natural process without, as far as we can determine, any anthropogenic basis. There's no real reason to believe that, absent a human presence, they wouldn't be slowly disappearing even now. So how do we preserve them while allowing that natural process to occur?

I don't have an answer to this question, of course. There isn't going to be one single answer; at the very least, it's going to depend upon the specific characteristics of the system in question. In our real world, it's also going to depend upon what we value about each site, and why, and far too often on what we can afford to do with that site. But as always, ignoring the question is just another way to answer it.

* There are a number of trees in North America called cedars. The original Cedar, (Cedrus libani), is in the family Pinaceae and occurs from Lebanon and Israel north into Turkey and east into Syria and Jordan. Three other species of Cedrus grow in the Himalayas (C. deodara), the Atlas Mountains of North Africa (C. atlantica), and the island of Cyprus (C. brevifolia). North of Mexico, species from 5 different genera (Thuja, Juniperus, Chamaecyperus, Calocedrus, and Cupressus) are graced with the name - they're all in the family Cupressaceae, or Cypress family.

(1) Grüger, E. (1972). Pollen and seed studies of Wisconsinan vegetation in Illinois, USA. Geological Society of America Bulletin, 83(9), 2715-2734.

Herons on ice.

The temperature actually reached 6 degrees today, so here's another shot from this weekend:

Great Blue Heron (Ardea herodias), Starved Rock Lock and Dam,
LaSalle Co, IL 1/24/2014

It seems odd to see a Great Blue Heron hanging out on ice -- it's hard to fish through, unless you have a drill. But it's become an expected sight in northern Illinois in the winter, if not a common one. They're what's sometimes termed a "half-hardy" species, meaning one that will only migrate as far as is necessary to survive. Some birds, inevitably, will misjudge that distance, and perish from cold and starvation.

That seems like the kind of selective pressure that should have pushed the species towards a more stereotypical migration pattern, where the birds keep going to a place that has little chance of freezing over, and therefore there's a much better chance of surviving. And yet, there he is, on that ice floe, and he wasn't alone. So what's going on?

The answer comes down to variation, in two places. First, the birds: each bird uses its own criteria to decide upon a wintering location, and those criteria vary based upon both the bird's physical condition and its genes. The second variation is, of course, the weather. In a cold winter, those birds at the "winter north" edge of the variation will likely die. But in a warm winter, those same birds save themselves much of the time and energy their "play it safe" southern neighbors are investing in migration. Which means that in those years, the risk-taking northern birds have more time and energy to invest in reproduction, and are likely to end up producing more offspring.

This sort of variation is important for a population to quickly adapt to shifts in its environment. Evolution is often presented as "when a beneficial mutation shows up, natural selection will cause it to replace the older version of the gene". But, as the Great Blue Heron above shows, most of those mutations actually happened many generations ago, and the necessary variation is already in the population, just waiting to go. Fixing one allele in a population through natural selection actually requires a fairly strong, consistent selective pressure over quite some time, which is unusual when we're talking adaptations to climate.

However, as our winter weather has warmed significantly over the last century, we've seen these half-hardy migrants wintering farther north than ever. As an example, Great Blue Herons were unrecorded on the Evanston Christmas Bird Count until 1969, and only averaged 0.6 per year until 1989. Since then, they've averaged 8 per year, with a high of 21 in 2012. (1) If we assume that this change is purely genetic (actually pretty unlikely -- most of these half-hardy birds probably incorporate a lot of behavioral plasticity in their genes), then the rate at which the population as a whole shifts will depend upon the basic reproductive rate of the population as well as how much better the risk-taking, northern birds actually do. But it's going to be a lot faster than if the population had to wait for the right mutations.

We have a tendency to think of a species as a thing, as an abstract that individuals rarely quite meet. But, as this heron shows, the abstract is our own mental construct. A species is actually made up of a bunch of individuals, each of them embodying a small part of the pool of variation that is a much more productive way of thinking about populations.

(1) National Audubon Society (2010). The Christmas Bird Count Historical Results [Online]. Available http://www.christmasbirdcount.org [1/27/2014]

A Good Year for Eagles

Spent the weekend at Starved Rock State Park, manning a table at the EagleFest, so:

Bald Eagles (Haliaeetus leucocephalus), Starved Rock State Park,
LaSalle Co, IL 1/26/2014

These are a few of the Bald Eagles that can be found just below Starved Rock Dam in the winter. This has been a particularly good year for them, I counted 40 or so, and that number will probably increase over the next month.

What has made it a good year? Ice -- lots and lots of ice. When the Illinois River freezes, they congregate below dams where the water remains open. It's the only place you can still catch fish, and the only place you can count on finding geese. So, even though you face some competition:

It's still worth being there. In a mild winter, with lots of open water, the eagles disperse up and down the river, and you don't see the big concentrations. This same pattern happens on the Mississippi River.

So a good year for Eagles isn't really a good year for the eagles, just the eagle watchers.

The same thing happens with migratory songbirds -- places like Point Pelee and High Island are known for fantastic concentrations of migrants. On good days, you can have warblers feeding almost between your feet!

But those good days come when birds moving north over water meet headwinds that exhaust them. While it's difficult to say how many birds fail to make the crossings (Lake Erie to Point Pelee, the Gulf of Mexico to High Island), Sillett and Holmes estimated that Black-throated Blue Warbler (Setophaga caerulescens) mortality rates increase 15-fold during migration. (1) Even inland, we see the same effect -- major fallouts occur when birds moving north meet a cold front coming south, and you end up with birds trying desperately to find food on a cold, often wet spring morning.

For a warbler, a good spring for migration means no more stopovers than absolutely necessary -- think business traveler, not tourist -- and the more of them you see in your backyard, the tougher the migration likely was for them.

So when you hear that this was a "good spring", stop and think about who it was good for.

(1) Sillett, T. S., & Holmes, R. T. (2002). Variation in survivorship of a migratory songbird throughout its annual cycle. Journal of Animal Ecology, 71(2), 296-308.

Clowns on the water

Another day down at Starved Rock watching eagles, so here's a shot from last fall:

Harlequin Duck (Histrionicus histrionicus),
Waukegan Beach, Lake Co, IL 11/16/2013

This female Harlequin Duck spent several days in the area, then moved on to who-knows-where. As you can see, they prefer to be in amongst the breaking waves, where they can dive to find their preferred foods, primarily small mussels. (Those would be Zebra Mussels here in Illinois -- a subject for a warmer day.) During the breeding season, they live on rivers, primarily fast-flowing ones in Alaska, British Columbia, and the pacific northwest. There is a smaller population in eastern Canada, where our Chicago birds probably come from, and they occur in Iceland and parts of northern Eurasia as well.

Here's a shot from Alaska, of a female just north of Nome, in her preferred breeding habitat. Given the date, she's probably on her way out to the coast and thence down to the Aleutians.

Harlequin Duck, north of Nome, AK, 8/10/2012

Males are impressive birds, but unfortunately, this is the only decent shot I have of one, from the Cincinnati Zoo:

Harlequin Ducks, female and male, Cincinnati Zoo, 3/29/2012

Google them for a real treat.

These guys have some interesting breeding strategies -- males and females pair up on the winter grounds, like many ducks, but unlike most ducks, Harlequins form long-term pair bonds. (1) The bond only goes so far, though. Once the female is done laying eggs, the male heads right back down to the ocean. This can be a problem for conservationists, since that means females only have the opportunity to lay one clutch, and if it fails, the entire season is a loss.

But how do they maintain long-term pair bonds if the males don't stick around? Well, both males and females show a high degree of winter philopatry (i.e. they keep going back to the same winter locations). (2) So the males and females end up finding each other again each winter. Even males without a mate return to the same place initially, although they may then move on. Most ducks, in contrast, only pair for one season, and males will follow females back to wherever the females hatched. (3)

This difference has interesting implications for differences in population structures, but that's a topic for another week.

 

 

(1) Smith, C. M., Cooke, F., Robertson, G. J., Goudie, R. I., & Boyd, W. S. (2000). Long-term pair bonds in Harlequin Ducks. The Condor, 102(1), 201-205.

 

(2) Robertson, G. J., Cooke, F., Ian Goudie, R., & Sean Boyd, W. (2000). Spacing patterns, mating systems, and winter philopatry in Harlequin Ducks. The Auk, 117(2), 299-307.

 

(3) Rohwer, F. C., & Anderson, M. G. (1988). Female-biased philopatry, monogamy, and the timing of pair formation in migratory waterfowl. In Current ornithology (pp. 187-221). Springer US.

Cold Turtle Soup?

I'm out of town today, so here's an old shot:

Painted Turtles (Chrysemys picta), Volo Bog State Natural Area, Lake Co, IL 9/26/2012

Here in Chicago, if we see a turtle in the winter, it's a wonderfully warm winter. They normally disappear for several months. But where do they go?

Other animals employ various strategies for surviving the winter, of course. Many birds migrate -- but if you've ever watched a turtle for very long, the thought of them migrating is rather amusing. Annual plants spend the winter as seeds and germinate in the spring, while many insects overwinter as eggs that hatch in the spring. But turtles are very long-lived, with large Alligator Snappers (Macrochelys temminckii) and Galapagos Tortoises (Chelonoidis nigra) being known to surpass the century mark, so that idea's out. Clearly they don't remain active; even if their food supplies remain available, their low metabolism means cold weather basically immobilizes them.

What's left? Well, hibernation, obviously. So where should a turtle hibernate? Box Turtles (Terrapene carolina) hibernate in shallow burrows (1), but the Painted Turtles pictured above spend the winter here:

Painted Turtle, Spring Bluff Forest Preserve, Lake Co, IL 6/29/2012

Well, at the bottom, anyways. The ice would get in the way of this sort of behavior.

Both of these hibernation sites pose problems, of course. Box Turtles are regularly exposed to temperatures below freezing, and they have been shown to actually resist a significant amount of ice in their intracellular fluids -- something that would painfully kill you or me. (1) Hatchling Painted Turtles are capable of this as well, as they overwinter in their below-ground nests. (2) As mentioned above, however, older Painted Turtles spend the winter at the bottom, where the temperatures are maintained just above freezing by the high specific heat of water and by the insulation of the ice at the surface. That ice, however, causes another problem: it keeps the turtles from reaching the surface, where they can actually breathe. So do they actually make it through an entire winter without even breathing?

Well, not quite. Turtles do have exceptionally low metabolic rates to begin with, so they aren't using too much oxygen. They also appear to be very tolerant of both hypoxia and lactic acidosis (lactic acid is produced when vertebrate cells metabolize sugar without oxygen -- a process that we know as fermentation). But some turtles have also been shown to extract oxygen from water in order to stretch things out; in other words, they can breathe underwater! This ability has been demonstrated in both Painted (3) and Loggerhead Musk Turtles (Sternotherus minor) (4) , but not in Red-eared Sliders (Trachemys scripta) (4), so it's not a universal turtle trait.

Turtles are the only terrestrial vertebrates I'm aware of that have regained the ability to breathe water; whales, dolphins, seals, sea snakes, marine iguanas, otters, even hippos all have to breathe air. Oxygen simply doesn't dissolve in water in sufficient quantity to support most terrestrial animals. Turtles can only manage it because of their low metabolic rates, another advantage of life spent in the slow lane.

The schoolboy version of the scientific method lists observation as the first step in the process. But as Sherlock Holmes once pointed out, sometimes the neatest questions come from the things you don't observe, like turtles on a cold winter day.

(1) Costanzo, J. P., & Claussen, D. L. (1990). Natural freeze tolerance in the terrestrial turtle, Terrapene carolina. Journal of Experimental Zoology, 254(2), 228-232.

 

(2) Storey, K. B., Storey, J. M., Brooks, S. P., Churchill, T. A., & Brooks, R. J. (1988). Hatchling turtles survive freezing during winter hibernation. Proceedings of the National Academy of Sciences, 85(21), 8350-8354.

 

(3) St. Clair, R. C., & Gregory, P. T. (1990). Factors affecting the northern range limit of painted turtles (Chrysemys picta): winter acidosis or freezing?. Copeia, 1083-1089.

 

(4) Belkin, D. A. (1968). Aquatic respiration and underwater survival of two freshwater turtle species. Respiration physiology, 4(1), 1-14.

 

Climate on the Small Scale

Another frigid day in Lake County:

Looks cold, huh? (It was around 8 degrees today, and only reached 12 yesterday.) But here's the odd thing -- icicles form when liquid water runs down to a point, and then freezes. (You can see this by the spatters of ice below them, where some of the ice managed to fall before freezing.) So how are these forming, given it's too cold for the snow to melt in the first place?

First, they could be left over -- we had some warmer weather a few days ago. But the roof above these is clear, and our most recent snowfall was after that thaw.

The answer, of course, is that the combination of sunshine on the roof and heat from below is what's melting the ice. In fact, though, despite the cold weather, the sun alone would be enough to raise the temperature on that roof above freezing -- our garage is dripping right now, and it's not heated at all.

So why I am I going on about snow melting on roofs? Well, say you're a little caterpillar in the fall, looking for a place to spend the winter. The difference between a spot where the sun shines part of the day (the south side of a tree, for instance) and one where it doesn't (the north side of the same tree) could well mean the difference between surviving and dying. Even if it doesn't, the extra warmth in the spring could mean an earlier emergence and therefore more time to eat and grow come spring.

Ecologists have a term for this concept, naturally. We talk about microclimates -- a fancy way of saying that temperature, sunlight, humidity, and so on vary considerably across the landscape, down to the smallest scales we care to measure.

Another example is the old canard about finding your way in the woods by looking at the moss, since it only grows on the north side of trees. (Incidentally, this is a great way to get really lost!) The reasoning behind this statement is this: the north side of the tree doesn't get any direct sunlight, so it's going to stay cooler, and therefore water won't evaporate as quickly, and the moss can survive there, but not on the warmer, drier south side. Of course, in many forests, no part of the trunk gets direct sunlight, and in many others, water is plentiful enough that it doesn't matter. But the basic idea actually does make some sense.

Some species require (or at least use) very specific microclimates -- some lichens only grow on the bark of one genus of trees, while some plants will only grown on soil derived from certain types of bedrock. Specifically, in California, many invasive grassland species won't grow on serpentine soils, apparently because of low levels of N and P, although these soils have other unique characters that may play some part. (1) This, of course, means that to see the native California grasslands, it helps to have a map of soil types. Here in Illinois, most of the state's remaining prairie remnants are known as hill prairies, since they grow on steep west-facing slopes -- steep because they couldn't be plowed or effectively grazed, and west-facing because east-facing slopes stay cooler, and trees are able to grow on them.

It sometimes seems like biologists focus on tiny, irrelevant details. But the living world is entirely composed of those little details, and to a little lichen the difference between an oak tree's bark and a spruce tree's bark isn't irrelevant -- it's life or death!

(1) Huenneke, L. F., Hamburg, S. P., Koide, R., Mooney, H. A., & Vitousek, P. M. (1990). Effects of soil resources on plant invasion and community structure in Californian serpentine grassland. Ecology, 71(2), 478-491.

A long winter's nap?

Busy day today -- the semester started, and I spent the morning at the eye-doctor, so here's another Colorado shot:

Fox Squirrel (Sciurus niger), Colorado Springs, El Paso Co, CO 1/1/2014

This little guy was quite busy that day, although he appeared rather miffed that I didn't have any nuts for him. Even around here, where the temperature almost reached 10 degrees today, his cousins are out and about all winter.

This little guy, on the other hand, disappears in November, and won't reappear until March:


Thirteen-lined Ground Squirrel (Spermophilus tridecimlineatus),
Illinois Beach State Park, Lake Co, IL  10/21/2006

And this one is fast asleep right now, but if we get a nice February thaw, he'll be out searching out lost acorns:


Eastern Chipmunk (Tamius striatus), Ryerson Conservation Area, Lake Co, IL 3/16/2012

Finally, the odd man out:

Grizzly Bear (Ursus arctos), Cheyenne Mountain Zoo, 12/27/2013

This guy will occasionally wake up on warm days -- if you ever find one active in the winter, keep your distance. He'll probably be hungry!

Unfortunately, I don't have a good shot of a marmot to add.

What's the theme here? Hibernation, of course. Whereas birds migrate instead (with one odd exception), most terrestrial mammals simply can't move far enough fast enough to make it worthwhile. So, if you want to live in an area where you can't get enough food over the winter, and your food doesn't keep well, what do you do? Eat all you can while you can, then spend the winter sleeping it off. And to stretch it a bit further, drop your metabolic rate so you're not burning so many calories. For most species, that means very slow heartbeats, very slow breathing rates, and very low temps -- Arctic Ground Squirrels actually experience below-freezing temps in some parts of their bodies! For a long time, it was thought that bears slept without hibernating, but later work indicates that they show reduced metabolism without noticeable temperature drops, apparently by reducing blood flow to peripheral tissues. (1)

But why so many patterns? Excluding the Fox Squirrel, we have two obligate hibernators (Thirteen-lined Ground Squirrel and the marmots), and two facultative hibernators (which means they only hibernate when they need to -- obligate hibernators enter hibernation whenever the environmental triggers are reached). Food is obviously a big part of the answer, specifically the predictability of winter food supplies. If you know that you're not going to be able to eat when you wake up, why bother? If you've got a good chance of finding a meal on the occasional warm days, it might be worth it.

Of course, waking is only "worth it" if the meal you might find gives you more energy than you're spending warming up. (You can hibernate at low temps, but you can't be active that way.) And the amount of energy it takes to warm up is greatly dependent upon how big you are. Calculations suggest that marmots are just about at the maximum size for a mammal to be able to warm up again on a consistent basis -- anything heavier may well not be able to store enough food to survive the winter and manage to get going again. Although there is a big difference between a marmot and even a Black Bear, the fact that bears hibernate at close to normal body temps does suggest that this idea holds some validity.

(1) Folk Jr, G. Edgar, Jill M. Hunt, and Mary A. Folk. "Further evidence for hibernation of bears." Bears: Their Biology and Management (1980): 43-47.

How do you keep those colors shining so bright?

Here's a nice Herring Gull (Larus argentatus) shot from today, taken as the birds came back in from the lake to the marina:

Herring Gull (Larus argentatus), North Point Marina, Lake Co, IL 1/20/2014

An interesting thing to point out here is the brown mottling on the head and neck. That's an indication that the bird's in basic plumage, which results from a pre-basic molt, replacing all (or most) of the bird's feathers. Some birds (not gulls) only have this one molt each year, but most have at least one more, known as a pre-alternate molt. Sensibly, the plumage this results in is known as alternate plumage. (In the vast majority of birds that have alternate plumages, the pre-alternate molt is partial, typically some head and body feathers, while the long tail and wing feathers are only molted once.) The terminology was worked out by Humphrey and Parkes in 1959. (1)

Here's a couple of other examples -- Mallards (ducks follow the same pattern but do some odd things with the timing):

Mallard (Anas platyrhynchos) male in alternate plumage,

Lincoln Park Zoo, 11/30/13

Mallard (Anas platyrhynchos) male in basic plumage,

Waukegan Beach, Lake Co, IL 8/6/2013

 

and Common Yellowthroats:



Common Yellowthroat (Geothlypis trichas) male in alternate plumage,
Wadsworth Savanna Forest Preserve, Lake Co, IL 5/4/2013

Common Yellowthroat (Geothlypis trichas) male in basic plumage,

Illinois Beach State Park, Lake Co, IL 9/14/13

This terminology has always bothered me a bit. When I first learned it, it seemed truly problematic -- why call one plumage alternate, as if it was something the bird just put on for the summer. Given that alternate plumage is usually the one the bird wears for breeding, it seemed that it was rather too important to be designated "alternate". Then I did some reading, and found out that while they do label the plumages and molts this way, the terms basic and alternate aren't actually derived from the plumages. Rather, they refer to the molt strategies -- the basic strategy being to replace all of your feathers once a year, and the alternate strategy being to add a pre-alternate molt. The advantage to this, of course, is that you can have bright feathers for breeding and dull feathers for hiding when you don't need to impress anyone. The disadvantage is that it takes energy to replace feathers.

But there's still the question of why the "basic" strategy deserves the name. Humphrey and Parkes argued that evolution generally proceeds from simple to complex, and therefore that the simplest strategy should be the ancestral state. I do have a problem with this approach -- specifically, the determination of the ancestral state is based on an assumption that turns out to be seriously wrong. (We've had the basic facts here since the 1860's, but it wasn't until 15 years ago or so that we really started to realize how wrong we were.)

I could concede that the ancestral strategy is expected to be the simplest, if the most recent common ancestor of modern birds was close to the earliest feathered critters. But it clearly wasn't. Based on molecular clock methods, Michael Benton argued that this ancestor lived approximately 100 million years ago, in the early Cretaceous. But he himself pointed out that this was 30 million year older than the most recent fossil evidence we have. (2) So it seems we can confidently assign a Cretaceous age to the last common ancestor of modern birds. But Archaeopteryx lithographica, the earliest bird we have a fossil of (at least traditionally), lived in the early Jurassic, 150 million years ago, and Hu Dongyu et al. reported finding well developed feathers even earlier. (3) Protofeathers have also been found in numerous non-avian theropod lineages, and possibly even ornithischian dinosaurs, all of which push the origin of feathers back long before the modern birds.

The reason this is important is that those early feathered dinosaurs and ancient birds must have molted their feathers as well, since feathers would have worn out the same way then that they do today. At what point organized molt strategies started to emerge is anyone's guess, of course, but given how widespread the alternate molt strategy is in modern birds, it's hard to imagine that it took most of the 70-100 million years that were available since that last common ancestor. Since we have at least 50 million years, and possibly closer to 100 million years, between the origin of feathers and that earliest modern bird, it seems likely that there were several different molt strategies already in place by the time that modern birds emerged. Given that the alternate strategy is more common in today's birds than the basic one, it's at least possible that the alternate strategy is the ancestral one, and basic strategies evolved by the loss of the alternate molt.

I realize that the current system isn't likely to change anytime soon, and I wouldn't want it too. Whether the assumptions it's based on are correct or not, it's widely used today, and changing it would cause more confusion than it would be worth. (The same reason why we continue to Latinize scientific names, I guess.) But just because we use the terms doesn't mean we shouldn't keep examining the assumptions hiding behind them.

(1) Humphrey, Philip S., and Kenneth C. Parkes. "An approach to the study of molts and plumages." The Auk 76.1 (1959): 1-31.

 

(2) Benton, Michael J. "Early origins of modern birds and mammals: molecules vs. morphology." BioEssays 21.12 (1999): 1043-1051.

 

(3) Hu, Dongyu, Hou, L., Zhang, L., & Xu, X. "A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus." Nature 461.7264 (2009): 640-643.

Of Windstorms and Bluebirds

It was a rather windy day today, so I did a little drive-by photography:

Eastern Cottonwood (Populus deltoides),
N. Unit, Illinois Beach State Park, Lake Co, IL 1/19/2014

This was taken at the site of our fall hawkwatch. We've named many of the trees that we see from that spot, so that we can point out birds to each other, and this one was named Tall Tree. The name wasn't given ironically -- at the time, it appeared to be the tallest tree in view. Then came July, 2011, and a record-breaking windstorm. It took down several of our trees in the North Unit of Illinois Beach, but the South Unit was hit very hard -- the park administrators estimated that half of the trees in the area were down. (The park as a whole encompasses 4600 acres, so that's a lot of trees.) The unit remained closed for 8 months as crews removed downed or partially downed trees. (Mostly in the campground and picnic areas -- in the nature area, they only worked close to trails.)

This was a once-in-a-lifetime event, a difficult sort of thing to study. But it opened up canopies in large areas of the park, produced a big pulse of downed wood, and overall changed many acres of habitat from Black Oak woodland to sand prairie and oak savanna. This was a major change in the ecological dynamics of a significant stretch of lakefront.

Now, here's another photo, from that same year:

Mountain Bluebird (Sialia curricoides), N. Unit, Illinois Beach State Park,
Lake Co, IL 11/12/2011

Prior to 2011, there had only been five records of Mountain Bluebird in Illinois. That's less than one every 20 years of records. In 2011, there were five more, which was frankly amazing -- who knows how many years we'll have to wait to see such an invasion again!

There has been a long history of ignoring rare events in ecological studies. Being rare, they're very hard to study, and attributing important aspects of an ecosystem to a rare historical event smacks of deus ex machina, without the justification of fiction. On the other hand, it's clear that the effects of an earthquake, hurricane, or volcanic eruption can indeed be a major factor in how an ecosystem functions for years afterwards. Ecologists today are beginning to work out methods of studying such events in a general sense. (1,2,3)

The same issue of rare, improbable events crops up in studies of evolution and biogeography. Alan de Quieroz addresses this in his recent work, The Monkey's Voyage, How Improbable Journeys Shaped the History of Life. (4) It's well worth reading, incidentally. Among other things, he points out how very different South America would look without one incredible voyage -- the crossing of the Atlantic Ocean (a narrower Atlantic Ocean back then, but still...) by a troop of ancestral monkeys. (Monkeys aren't normally thought of as sailors, for good reason!)

Of course, events that only occur once in a lifetime are hard to study, and it's easy to see why biologists might prefer to focus on the slow, ongoing processes of everyday life. But it's worth remembering that other species operate on other timescales. A White Oak may live 500 years -- what we think of as once-in-a-lifetime, a tree might have to deal with 5 or 6 times. Bristlecone Pines live for thousands of years, as do some lichens -- a 500-year drought is nothing new. And some ecosystems change on even longer timescales, which makes "rare" events commonplace.

Of course, quantifying these occurrences and their effects is a challenge, but it may be one that amateur naturalists (especially birders) can help with. Birds wander quite a bit, with a species' occurrence in a particular place being a function of distance, the bird's dispersal abilities and migratory status, and things like winds and stopping points along the way. (The number of observers looking for them does complicate things, of course.) That gives us a nice range of probabilities to compare and, perhaps, fit into a more general understanding of how rare events might impact a system.

(1) Jentsch, Anke, and Carl Beierkuhnlein. "Research frontiers in climate change: effects of extreme meteorological events on ecosystems." Comptes Rendus Geoscience 340.9 (2008): 621-628.

 

(2) Schwinning, Susan, et al. "Thresholds, memory, and seasonality: understanding pulse dynamics in arid/semi-arid ecosystems." Oecologia 141.2 (2004): 191-193.

 

(3) Frei, Christoph, and Christoph Schär. "Detection probability of trends in rare events: Theory and application to heavy precipitation in the Alpine region." Journal of Climate 14.7 (2001): 1568-1584.

 

(4) de Queiroz, Alan. The Monkey's Voyage, How Improbable Journeys Shaped the History of Life. (2014). Basic Books, New York.

Snowy Owl on the Prowl

An afternoon visit to North Point Marina yielded a nice surprise:

Snowy Owl (Bubo scandiaca), North Point Marina,
 Lake County, IL, 1/18/2014

This is one of quite a few that have come down into the US this year. They breed on the Arctic tundra, in both Eurasia and North America (a distribution referred to as Holarctic). Some of them (mostly adult males) will spend the winter over much of that range, but many of them migrate south. In a typical year, a few will reach as far south as Chicago. In an atypical year like this one, there may be several dozen in Illinois. This year, one has been reported as far south as Jacksonville, Florida!

This sort of pattern is actually not uncommon for birds of prey from the Arctic -- Rough-legged Hawks, Gyrfalcon, and Snowy Owls all occasionally irrupt southwards in large numbers, as do Boreal and Great Gray Owls and Northern Goshawks from the taiga forest just south of the tundra. In some cases, (especially Northern Goshawks) smaller, localized irruptions can show a cyclical pattern -- every 10 years, for instance.

What's driving this? Well, this video holds the answer (keep an eye on the upper right at the base of the rocks):

As we often see, the answer is food! Specifically, the tendency of arctic rodents to undergo large, periodic swings in population size. Lemmings, of course, are famous for this, but perhaps the best data set showing these swings comes from Snowshoe Hares (Lepus americanus) in Canada. A century of trapping both hares and Canadian Lynx (Lynx canadensis) by the Hudson Bay Company means that we have a full century of population estimates for both species, and Lynx numbers follow hare numbers almost perfectly over a repeating ten-year cycle. (1) This cycle appears to be driven by a combination of Lynx predation on hares and the overbrowsing of food supplies by hares during the high parts of the cycle. (2)

Snowy Owls, on the other hand, don't show such a cycle -- when they come south, it tends to be in just one part of the country (West, Midwest, or East -- this year we're seeing a historic movement into the East spilling into the Great Lakes), but there's no apparent regularity to these irruptions. (3) Why the difference? Well, Snowy Owls moving this far south are just the vanguard of a larger movement. Any irruption similar to this year's means a lot of birds moving, which in turn means that they're coming from a very large area. So there must have been a collapse of Lemming and other rodent populations across a very large area. If there is any geographic structure to those populations, then in a normal year only small regions within that area would show a collapse, and we would only expect localized irruptions. Small enough ones would actually explain the normal annual variation that we see in southern Snowy Owl populations. Similarly, the more species the owls are able to prey upon, the more prey cycles would have to line up in order to create a poor enough year to drive them south.

So when you're out watching a Snowy Owl on the prowl, stop and think about the poor little lemmings that helped send that owl south to you.

(1) Elton, C. and M. Nicholson. 1942. The ten-year cycle in numbers of the lynx in Canada. Journal of Animal Ecology 11:215–244.

(2) Krebs, Charles J., Boonstra, R., Boutin, S., & Sinclair, A. R. 2001. "What Drives the 10-year Cycle of Snowshoe Hares?" BioScience 51.1: 25-35.

(3) Kerlinger, P., M. Ross Lein, and Brian J. Sevick. 1985. "Distribution and population fluctuations of wintering snowy owls (Nyctea scandiaca) in North America." Canadian journal of zoology 63.8: 1829-1834.

Of Little Acorns do Blue Jays Grow?

An interesting little still-life from today:

White Oak (Quercus alba) acorn caps, Van Patten Woods Forest Preserve,
Lake County, IL, 1/17/2014

Why acorns? Back to that in a moment.

The most noticeable bird (partly because they're so noisy) in the woods today was this:

Blue Jay (Cyanocitta cristata), Illinois Beach State Park,
Lake Co, IL  5/4/2012

This year Blue Jays have been particularly easy to find here in Lake County. This isn't always the case -- Waukegan CBC numbers, since 1980, have varied from 9 to 276, while Evanston CBC numbers have varied from 7 to 159. The correlation between the two counts, by year, is highly significant -- low years are low for both counts, and high years are high for both counts. (1) What causes these? While weather would certainly be a possibility, this year has been a rather hard winter so far, and it appears to be a very good year for Blue Jays. So that's probably not it. The other favored explanation for winter abundance, of course, is food. And that's where the acorn caps come in -- acorns and other nuts are a favored winter food for Blue Jays. And oaks and hickories show an interesting bit of natural history -- they tend to vary considerably from year to year in how many nuts they produce. Even more interestingly, the trees in a given region all tend to vary the same way -- a good year for one tree is usually a good year for most of the trees around them.

The argument usually given for why this happens goes like this: predators love to eat acorns, hickory nuts, etc. If we put out the same number of nuts every year, then the predator population will quickly grow to the point that none of our offspring will survive. On the other hand, if we spend several years just saving our energy, then put out a whole big bunch of acorns all together, then the predators won't be able to build up, and we'll overwhelm them with numbers so that some of our offspring are bound to survive. This makes sense, although I continue to wonder about the signals that trigger this united front -- is it just weather conditions over the course of the summer, or is something else going on that we're not seeing?

In any case, a good Blue Jay winter in Northeast Illinois probably implies a good mast year. (Mast is a general term for fruits and nuts produced by trees.) Another indication of this is that Red-headed Woodpecker numbers tend to vary in very similar ways to Blue Jays -- good Blue Jay years are usually good Red-headed Woodpecker years, etc. (1) Interestingly, in Missouri, this doesn't seem to be the case -- Blue Jay numbers tend to be independent of mast production, although Red-headed numbers do vary with mast production. (2) Perhaps they're far enough south that Blue Jays manage to find other winter foods in sufficient abundance to winter regardless, while up here they can't do it without acorns?

Other species show similar responses -- mice and chipmunks in Virginia showed increased winter survival and offspring survival in good mast years (3), and Black Bears in New Mexico showed dramatically decreased birth rates (down 60%) and recruitment rates (down 70%) after particularly poor acorn crops. (4)

This straightforward story does have a potential problem, though, at least in the eastern United States. One of our most noble hardwood trees, the American Chestnut, largely disappeared in the early 20th century as the result of an introduced fungus, the Chestnut Blight. Like the European Chestnut, the American Chestnut was an important mast tree. Unlike our oaks and hickories, it's production was reasonably constant from year to year. (5) Since it made up roughly 25% of the eastern hardwood forests, it's relatively sudden loss not only decreased the available winter food supply for a lot of species (and their predators, by extension), but it apparently drastically increased the annual variability, which must have had impacts we haven't even guessed at yet.

Of course, we're well outside of the Chestnut's historic range, so the blight probably hasn't had any effect here that we could detect. And that means that the Blue Jays and Red-headed Woodpeckers have probably been making decisions on where to spend the winter by looking for those little acorn caps for as long as they've been here for us to wonder about.

(1) National Audubon Society (2010). The Christmas Bird Count Historical Results [Online]. Available http://www.christmasbirdcount.org [2014]

(2) Smith, Kimberly G., and Todd Scarlett. "Mast production and winter populations of red-headed woodpeckers and blue jays." The Journal of wildlife management (1987): 459-467.

(3) Wolff, Jerry O. "Population fluctuations of mast-eating rodents are correlated with production of acorns." Journal of Mammalogy (1996): 850-856.

 

(4) Costello, Cecily M., Jones, D. E., Inman, R. M., Inman, K. H., Thompson, B. C., & Quigley, H. B. "Relationship of variable mast production to American black bear reproductive parameters in New Mexico." Ursus (2003): 1-16.

 

(5) Diamond, Seth J., Giles, R. H., Kirkpatrick, R. L., & Griffin, G. J/ "Hard mast production before and after the chestnut blight." Southern Journal of Applied Forestry 24.4 (2000): 196-201.