The Beaches are Filling Up!

First shorebird of the year!

Killdeer (Charadrius vociferus), Illinois Beach SP, Lake Co, IL  3/14/2014

This is a Killdeer (Charadrius vociferus). (They don't really hunt deer, that's a rendering of one of their common calls.) They occasionally winter as far north as Chicago, so it's probably not surprising that they are typically one of the first back in the spring, occasionally showing up here in Lake County in late February. They are also one of three species of shorebirds that breed commonly in this area -- most of our shorebirds nest either along the coast or on the Arctic tundra, with several more species using the boreal forests of Canada and Alaska.

Given that they are common, widespread, and conspicuous, it's hardly surprising that they've been the focus of quite a bit of research. Some of that has focused on migration and wintering behavior, but much of it has focused on this stage of their life:

Killdeer (C. vociferus) nest, N. Pt. Marina, Lake Co, IL,  5/26/2003

This, obviously, is a Killdeer nest -- and yes, they really do just dig a bit of a scrape in the gravel, and trust mostly in the camouflage pattern on the eggs to hide them when neither parent is on the nest. This is a monogamous species where both parents incubate, and if a female loses her mate, she is usually unable to hatch the eggs on her own. (1, 2) Males can manage to reach hatching, but even then their success rate is considerably lower.

We usually expect male and female animals to put equal amounts of energy into reproduction, although they allocate it differently. In Killdeer, males put more energy into mating displays, and females put more energy into the actual reproductive effort. (Eggs are expensive.) Both sexes put equal amounts of energy into parental care. But since their nests tend to fail at a rather high rate, females end up putting more energy, on average, into a given nesting season. (2) Probably as a result, they spend more time foraging than males. (1) Put it all together, and we have a nice neat explanation for why they are monogamous. Since females are unable to raise offspring without help, any male that doesn't stick around won't leave any offspring at all, no matter how successful he is at mating.

Surprisingly, in shorebirds, some polygamous species are polyandrous, meaning that one female mates with several males. Most polygamous species of birds are polygynous, which makes sense since the females are the ones putting lots of energy into producing eggs and raising offspring. But as we saw with the Killdeer, many species of shorebirds have males that put a lot of energy into raising their own offspring. So the system best known in Phalaropes can evolve, with females competing for multiple males.

When we see this sort of thing in the usual way, sexual selection often ends up producing bright, colorful males and dull, drab females. Here we have a test: if females are competing for males, they should be the bright ones. And what do we see?

This is a male Wilson's Phalarope (Phalaropus tricolor).

Wilson's Phalarope, (Phalaropus tricolor),
Quivira NWR, Stafford Co, KS 5/23/2013

And this is a female Wilson's Phalarope:

Wilson's Phalarope (P. tricolor),
Quivira NWR, Stafford Co, KS 5/23/2013

Sharp-looking bird, isn't she?

When we're using the comparative method to examine theoretical predictions, we need a speciose group with considerable variation in the traits we're interested in. Frequently, the shorebirds fit the bill.

And the first Killdeer of the season is always a welcome reminder of spring!

Killdeer (C. vociferus), N. Pt. Marina, Lake Co, IL  3/31/2013

(1) Brunton, D. H. (1988). Sexual differences in reproductive effort: time-activity budgets of monogamous killdeer,< i> Charadrius vociferus</i>. Animal Behaviour, 36(3), 705-717.

(2) Brunton, D. H. (1988). Energy expenditure in reproductive effort of male and female Killdeer (Charadrius vociferus). The Auk, 553-564.