Are Y'all Listening to Me?

by Karen Slagle

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Are Y'all Listening to Me?

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Karen Slagle

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Description

The eastern bluebird is found east of the Rockies, southern Canada to the Gulf states, and southeastern Arizona to Nicaragua. The increase in trees throughout the Great Plains during the past century due to fire suppression and tree planting facilitated the western range expansion of the species.[13] as well as range expansions of many other species of birds.[14][15][16] From 1966-2015 the eastern bluebird experienced a greater than 1.5% annual population increase throughout most of its breeding and year-round ranges, with exceptions including southern Florida and the Ohio River valley.[17]

Bluebirds tend to live in open country around trees, but with little understory and sparse ground cover. Original habitats probably included open, frequently burned pine savannas, beaver ponds, mature but open woods, and forest openings. Today, they are most common along pastures, agricultural fields, suburban parks, backyards, and even golf courses. Populations also occur across eastern North America and south as far as Nicaragua. Birds that live farther north and in the west of the range tend to lay more eggs than eastern and southern birds.[18]

An isolated, insular subspecies of the eastern bluebird is found on Bermuda, and has a distinctive, brighter blue coloration compared to mainland populations. This population was formerly thought to have been predated the colonization of the islands (making it one of only three extant, resident pre-colonization Bermuda landbirds, alongside the Bermuda white-eyed vireo and gray catbird). However, analysis of fossil strata found no evidence for the existence of bluebirds on the islands prior to European colonization. Using simulations and molecular evidence, a 2013 study found that the Bermuda bluebirds likely descend from very small founder population from a single colonization event during the 1600s. This colonization event could either be a natural one by migratory individuals or an anthropogenic introduction by early settlers, who are known to have introduced several other eastern North American birds like the northern cardinal (Cardinalis cardinalis) to Bermuda very shortly after colonization. It is likely that the alteration to the islands' ecosystem due to the clearing of native forest facilitated this colonization by providing optimal bluebird feeding habitat, along with a lack of predators.[19][20]

Behavior and ecology
Eastern bluebirds are social, and will sometimes gather in flocks of over a hundred. However, they are territorial during the breeding season and may continue to defend a feeding area throughout the winter.


Eastern bluebird

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Calls and songs of the eastern bluebird.
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Breeding

Eggs
Mating occurs in the spring and summer. A mature female typically raises two broods each season. Nests are constructed in trees within abandoned woodpecker holes or other cavities that provide adequate protection (usually several feet above ground). Construction of the nest is done primarily by the female and takes around 10 days to complete. These nests are small, cup-like structures lined with grass, feathers, stems, and hairs. Each female lays three to seven light-blue or, rarely, white eggs. The female incubates the eggs, which hatch after 13 to 16 days. The young cannot care for themselves upon hatching. The female broods the chicks for up to seven days after hatching. Fledglings then leave the nest 15 to 20 days after hatching.[11]


Juvenile (left) with parent
Eastern bluebird (Sialia sialis) at nesting box
Eastern bluebird (Sialia sialis) at nesting box
Both parents cooperate in raising the young, which they feed a diet consisting almost entirely of insects. Some young stay around the nest to help raise another brood. Fledglings are grayish in color, with speckled breasts. The blue color becomes much more prominent and the speckles on their breasts disappear as they mature. Bluebirds may begin breeding the summer after they are hatched.[11]

Eastern bluebirds can live for 6 to 10 years. The longest recorded lifespan for a bluebird is 10 years and five months.[18] However, most bluebirds die within their first year of life. Starvation and freezing are a danger to the young, but most threats come from other animals, including humans. Natural predators of eggs and nestlings can include eastern chipmunks, flying squirrels, American black bears, fire ants, and raccoons. Bluebirds of all ages (including adults) are threatened by rat snakes, racers, American kestrels, and domestic cats. Introduced species such as European starlings and house sparrows are competitors for nesting sites. Non-nesting adults face predation by all native species of falcons, owls, and most varieties of hawks, particularly those in the genus Accipiter. When approached by a predator, the male makes a song-like warning cry. If no male is present, a threatened female will begin to sing, hoping to attract a protective male back to the territory. Both males and females also flick their wings and warble when predators are nearby.[11]

Food and feeding
About two thirds of an adult bluebird's diet consists of insects and other invertebrates. The remainder is made up of wild fruits or berries. It has a preference for grasshoppers, crickets, katydids, and beetles; and will also eat earthworms, spiders, millipedes, centipedes, sowbugs, and snails.

Bluebirds feed by perching on a high point, such as a branch or fence post, and swooping down to catch insects on or near the ground. The availability of a winter food source will often determine whether or not a bird will migrate. If bluebirds do remain in a region for the winter, they group and seek cover in heavy thickets, orchards, or other areas in which adequate food and cover resources are available.

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May 31st, 2023

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