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Cave Swallow Life History



Cave Swallows nest in caves, sinkholes, and more recently under bridges and in culverts. They forage over open areas frequently near water.

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Cave Swallows eat flying insects on the wing, foraging at heights up to 350 feet. They consume numerous flying insects such as seed bugs, assassin bugs, short-horned grasshoppers, green lacewings, ladybird beetles, aphids, moths, wasps, bees, and flies. They usually feed in loose flocks throughout the day. They also drink water on the wing, gently skimming the surface of the water with their bill.

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Nest Placement


Cave Swallows nest colonially on vertical walls or horizontal ledges, sometimes sharing the area with Cliff Swallows. Historically Cave Swallows only nested in caves or sinkholes, but they now also nest on highway underpasses and culverts. They reuse nests from the previous breeding season, refurbishing them until the weight of the nest causes it to break from the wall.

Nest Description

Males and females collect mud and bat guano with their bills to create a flattened cup made of mud pellets. Sometimes the sides of the nest extend upward to enclose the cup and may have a small entrance tunnel on one side. They line the inside of the nest with grass and plant fibers.

Nesting Facts

Clutch Size:1-5 eggs
Number of Broods:1-2 broods
Egg Length:0.8-0.9 in (1.9-2.2 cm)
Egg Width:0.6-0.6 in (1.4-1.6 cm)
Incubation Period:15-18 days
Nestling Period:20-22 days
Egg Description:White, with fine dark spots.
Condition at Hatching:Naked and helpless.
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Aerial Forager

Cave Swallows fly with deep and strong wingbeats interspersed with frequent glides. When they enter a cave, they float down into it and fly back out in a spiral. They spend most of their time aloft, but head to the ground to collect tiny balls of mud or bat guano to build a nest. They collect mud after recent rains or along the edges of rivers and springs with moist soil. While on the ground, they continually flutter their wings, which scientists suggest could be to confuse predators, to prevent their wings from touching the ground and getting soiled, or to discourage unwanted advances from males, which often attempt to mate with females while they are on the ground. They nest in colonies and forage in single-species groups as well as with other swallows.

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Low Concern

Cave Swallows are common and their populations increased dramatically between 1970 and 2014, according to Partners in Flight. The estimated global breeding population is now at 6.8 million. The species rates an 8 out of 20 on the Continental Concern Score, which means it is not on the Partners in Flight Watch List and is a species of low conservation concern. Since the mid 1980s, Cave Swallows have noticeably expanded their range, now occupying Texas and Florida where they nest under bridges and culverts. Cave Swallows are also likely benefitting from increases in irrigated agriculture in the Southwest, which provide good foraging opportunities.

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