Life and Love in the Cattails

My first sure sign of spring, on a day that reached 45 degrees:

Red-winged Blackbird (Agelaius phoeniceus),
Spring Bluff FP, Lake Co, IL 5/16/2012

This beauty is a Red-winged Blackbird (Agelaius phoeniceus). The species is one of the most common birds in North America, with some Gulf Coast Christmas Counts reporting over 1,000,000 each! During the winter they usually roost and feed in large (often very large) flocks, but come spring the males become territorial -- sort of. They defend a territory within the marsh or wet field that they prefer to nest in, but it's a fairly small territory, and they routinely leave it to find food. It is typically big enough for several females to nest in, though, and males are typically polygynous.

The first bird was a male, this is a female:

Red-winged Blackbird (Agelaius phoeniceus),
Half-day FP, Lake Co, IL 5/19/2012

Typically, when we see this sort of dimorphism, it means that the males are competing for access to females, either by holding desirable territories or by attracting females based on some signal of male quality. In this species, it is clear that males are competing for territories, but it's less clear that a male's territory correlates with his quality. It's even less clear that females are looking for the brightest males. (1) What is clear is that males treat the red and yellow epaulets as territorial signals -- males that have them blackened have trouble gaining territories, (2) and males will respond aggressively to quite abstract models if they have red patches on them.

The combination of small breeding territories and localized habitats means that Red-winged Blackbirds tend to nest in loose colonies, with quite a few neighbors and females routinely crossing other males territories. As a result, extra-pair paternity is quite common in this species. Males don't seem to show any awareness of the paternity of their broods, though, since their paternal effort didn't correlate at all with their actual paternity. (3)

Given their abundance, their extensive range, and their economic impacts (blackbirds of all species consume a considerable amount of corn and other grain crops) it's not surprising that Red-winged Blackbirds are one of our most studied species. Birder's often have a bias of sorts against common species (it's just a Red-winged Blackbird), but there's an inherent contradiction here -- if we're celebrating rarity rather than abundance, then we're aiming at the wrong target.

(1) Yasukawa, K. (1981). Male quality and female choice of mate in the red-winged blackbird (Agelaius phoeniceus). Ecology, 62(4), 922-929.

(2) Smith, D. G. (1972). The role of the epaulets in the red-winged blackbird,(Agelaius phoeniceus) social system. Behaviour, 251-268.

(3) Westneat, D. F. (1995). Paternity and paternal behaviour in the red-winged blackbird,< i> Agelaius phoeniceus</i>. Animal Behaviour, 49(1), 21-35.