Wild Bird Center of Boulder APRIL '10 eNewsletter

Cattail Casanova by Steve Frye

It is said that in spring, a young man's fancy turns to love. This is certainly true of male yellow-headed blackbirds. With luck, strength, and determination, a male yellow-head acquires and defends the choicest territory in the marsh. A good territory will assure him not only one mate, but several.

In early spring, our marshes come alive as red-winged blackbirds come back to claim the cattails. Their reign is short, however, and before long the larger yellow-headed blackbirds return to rule. Yellow-heads nest communally and will take the largest sections of cattails away from the red-wings. Yellow-heads will only nest in cattails above two to four feet of water. Red-winged blackbirds are generalists and will nest in a variety of situations, so being pushed out to the marsh margins by the yellow-heads does not greatly affect their nesting success.

yellow-headed blackbird

Each male yellow-headed blackbird tries to grab the largest and best piece of habitat it can hold against its neighbors. It will aggressively defend its territory from invasions by other male yellow-headed blackbirds (intraspecific territoriality) and from red-winged blackbirds, marsh wrens, bitterns, hawks, and others (interspecific territoriality). Yellow-headed blackbirds advertise their territory and try to attract mates just like other songbirds do, with song. Their song is not exactly melodic, but has a raucous, brash beauty just like the birds themselves. Roger Tory Peterson described their song as "low, hoarse rasping notes produced with much effort; suggests rusty hinges." Even less complimentary is the National Geographic's Song and Garden Birds account, "no great musicians, the yellow-heads sing a harsh jumble of notes ending in a rasping buzz. The songs are accompanied by twisting and writhing as if the birds were in agony." It doesn't matter what we think about their nasal, raspy notes and buzzes, for they do seem to have the desired affect on female yellow-heads.

The reproductive scheme of yellow-headed blackbirds is polygyny, the mating of one male to many females, but the female mating only with one male (or so he thinks). Polygyny arises in some species when the reproductive investment of one partner is low, when there is limited appropriate habitat, and when one parent can provide sufficient care for the young. A species that requires both parents to successfully raise young (e.g. black-billed magpies) could not be successfully polygynous.

Male yellow-headed blackbirds have a low reproductive investment (they only produce sperm). Yellow-heads also have very specific habitat requirements, and within the appropriate habitat only a few choice areas exist. Therefore, it is an advantage for multiple females to pick the male with the choicest spot. Another key factor influencing polygyny is parental care.

Once the female has made her mate choice, she will build a nest on the male's territory while the male tries to keep other males from copulating with her. Yellow-heads build their nests of wet vegetation several inches to several feet above the water. As each nest dries, it tightens and draws in the supporting vegetation. Females usually lay four eggs in early to mid-May, and the young fledge in mid-June.

In Colorado, yellow-headed blackbirds are a species of special concern, meaning their population has shown a downward trend. This is largely due to habitat loss. Unlike many other songbirds, yellow-headed blackbirds are not affected by cowbird parasitism.

Over the last few years in Boulder County, the population of yellow-headed blackbirds has been quite variable both in numbers and locations. Traditionally, one of the best places to view these conspicuous and raucous birds was the boardwalk area of Cottonwood Marsh at Walden Ponds, but the water levels have been low and the cattail regions have suffered in the past few years. This year the water levels are quite high in many Boulder County locations including Walden Ponds. So I am looking forward to good numbers of yellow-heads giving us great shows at Sawhill and Walden Ponds, as well as other locations like Boulder and Union Reservoirs. See if you can spot the males with the best territories and largest harems.

Yellow-headed Blackbird audio on RingTones

Yellow-headed Blackbird at Crex Meadows on Youtube
Yellow-headed Blackbird profile from All About Birds
Yellow-headed Blackbird video #1 from the Macaulay Library

Yellow-headed Blackbird video #2 from the Macaulay Library
Yellow-headed Blackbird photos by Bill Schmoker