An Imperial Beach Hidden Gem and “Dig IB” Bird of the Week, the Cassin's Kingbird
Feb 01, 2018 11:12AM
By Paul Spear
This weekly column provides photos of birds photographed locally in the Tijuana Estuary or on IB's beaches along with background on the bird.
This week’s “Bird of the Week” is Cassin's kingbird (Tyrannus vociferans), a large tyrant flycatcher native to western North America. The name of this bird commemorates the American ornithologist, John Cassin. They are still widespread and common.
As suggested by its scientific name vociferans, Cassin's is our noisiest kingbird (except for the very localized Thick-billed). Possibly it has more need for vocal communication because it lives in denser habitat than most. Males have a strident "dawn song," a rising berg-berg-berg-BERG, often heard at first light but rarely later in the day, sometimes confused with song of Buff-collared Nightjar. Where present in numbers (as on wintering grounds in Mexico), flocks may gather to roost in large concentrations.
Habitat is in semi-open high country, pine-oak mountains, and in groves. In breeding season they favor more wooded habitat than most kingbirds, and ranges to higher elevations, although their habitat may be in places that overlap with Western Kingbirds. Cassin’s kingbirds nest in open pine forests, pinyon-juniper woodlands, oak woodlands, and streamside trees at lower elevations, and may also nest in groves of eucalyptus. During migration and in winter they can be found in more open habitats.
Cassin’s kingbirds feed from a perch in a tree or on an exposed wire, flying out to capture flying insects in mid-air. They may also fly out and hover while picking up insects or other arthropods from leaves or from the ground. Diet is mostly insects, and some berries. They feed on a wide variety of insects, including wasps, beetles, caterpillars, moths, grasshoppers, true bugs, flies, and many others, as well as some spiders. They also eat some berries and fruits, more than most flycatchers.
After mating, females lay 3-4, up to 5, creamy white with brownish mottling eggs. Markings are
often concentrated near the large end of the egg. Incubation is by females, in about 18 days. Both parents feed nestlings. Young leave the nest after 14-17 days. Broods are usually 1 per year, but they may raise 2 broods in the southern part of range.
Males have a fast zigzag courtship flight. Members of a pair may perch together in nest trees, calling and quivering wings. Adults actively harass larger birds (such as ravens and hawks) in the vicinity of their nests, but may tolerate other species of kingbirds nearby. Nest sites are in a large tree such as sycamore, cottonwood, oak, or pine, placed on a horizontal or near-horizontal branch, often well out from the trunk. Nests are usually 20-50' above the ground, but may occasionally be lower and sometimes much higher. Nests are a bulky cup of twigs, weed stems, rootlets, leaves, feathers, hair, and debris, lined with finer plant fibers and other material.
Cassin's kingbirds are not commonly seen in the Tijuana Estuary. I was lucky to spot this one perched on the power line along the helicopter field fence. Look for this winter visitor or one of the many other birds living there. Until next week, good birding!
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