Eastern Bluebird (Sialia sialis)
Habitat and Habitat Utilization
Range
Eastern Bluebirds range eastward of a line from Ontario down to Arizona. The northern limits of the range are southernmost Canada. There is also a small population in central Mexico.
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Habitat
Eastern bluebirds prefer edge or open habitats with little ground cover. Bluebirds are cavity nesters, and are unable to excavate their own cavities, so they rely on those made by other species, or naturally occurring cavities. Because of this, nest cavities are the limiting resource in most populations (Gowtay and Plissner 1998).
Diet
Bluebirds are ground foragers and feed primarily on insects and small fruits. Individuals forage in open habitats with very little ground cover. They use perches to survey the ground below them to stage their foraging attempt, and then fly to the ground when a prey item is located. Bluebirds have great eyesight, as they can identify prey items from as far as 40m away. During breeding season, most foraging is done in the morning hours, followed by the evening hours; almost no foraging occurs during the afternoon (Gowtay and Plissner 1998).
Predation
Rat snakes are known for feeding on cavity nesting birds, and they are the number one predator of eastern bluebirds in the piedmont region of North Carolina. Rat snakes have the ability to climb trees, fence posts, and nest poles to reach a nest cavity, and often prey on incubating females, nestlings, and bird eggs. Rat snakes are diurnal, so bluebird nests are constantly vulnerable to predation. Male bluebirds are often able to successfully deter a rat snake during the day. However, because adult bluebirds do not spend the night in their nest cavity, nocturnal attacks are unchallenged (Hensley and Smith 1986).
Hensley and Smith (1986) observed in two recorded instances of nocturnal nest predation by rat snakes, the male bluebirds return to the nest periodically after the predation and search for their female mate, as well as their offspring. One male continued to bring food items back to the nest. After about 24 hours, one male abandoned the nest box, while the other male began singing in attempt to find another mate.