Swallows around Kachemak Bay
Kachemak Currents is a podcast and radio segment produced weekly by the Center for Alaskan Coastal Studies. This segment originally aired on KBBI public radio (AM 890) on July 23, 2024, and was written and recorded by Wynn Nature Center and Inspiration Ridge Preserve naturalist Robyn Walker-Spencer. For more episodes of Kachemak Currents or to listen live, visit KBBI online.
Welcome to Kachemak Currents, brought to you by the Center for Alaskan Coastal Studies.
As we reach mid-July, we can officially mark the end of the swallow breeding season! Around the Kachemak Bay for the past month, little nestlings have hatched, slowly developing feathers over their pink skin, opening their eyes, and preparing to flee the nest. After 20 days, tree swallow young weigh as much as their parents and are ready to fly as they leave home for the first time.
The tree swallow (Tachycineta bicolor), one of Kachemak Bay’s two species of swallows, is found across northern North America. Tree swallows are acrobatic fliers, and are easy to spot twisting and turning in the air to hunt insects. They prefer to live in open areas, especially near bodies of water that can provide plenty of flying insects for prey. Despite preferring fields, marshes, and swamps for habitats, they rely on cavities in old trees in order to build their nests during the summer, which is their breeding period.
A borescope image shows a swallow sitting on a clutch of eggs in a nest box at Inspiration Ridge Preserve. How many eggs can you see?
This reliance on trees for reproduction is likely one of the reasons tree swallows are declining–their population decreased 30% from 1966 to 2019. Their numbers are most limited by nest site availability (those cavities in old trees), which have been disappearing in the last 200 years as people clear forests, cut down older trees, and remove dead trees. With fewer nests, fewer swallows can reach adulthood.
Tree swallows are also susceptible to shifts brought on by climate change. Swallow eggs are now laid nine days earlier on average due to warmer temperatures. Insect availability, which they rely on as a food source, is also weather dependent. A study from 2020 suggests that climate change-driven patterns in weather (including temperature and rainfall) drives insect numbers–which is correlated with lower swallow survival.
Although tree swallows are in decline in Alaska, supporting their chick rearing could help boost their population.
However the range of the tree swallow is actually expanding, likely due to an increased use of nest boxes as a conservation strategy. For tree swallows, nest boxes serve as an alternative to tree cavities when nesting options are limited. And they work! A study from 2018 in British Columbia found that swallows using nest boxes had larger clutches and a higher chick hatching rate than swallows using tree cavities. Swallows do well in nest boxes near bodies of water and will often line their nests with feathers.
Naturalists monitoring a nest box at Inspiration Ridge Preserve using a borescope–a small camera that allows researchers to view the contents of the box without disturbing the nest.
Organizations like NestWatch, run by the Cornell Lab of Ornithology, set up citizen science programs to encourage use of nest boxes and to make swallow monitoring more accessible. You can help provide tree swallows with nesting habitat by placing nest boxes on your property. Although tree swallows are in decline in Alaska, supporting their chick rearing could help boost their population. Keep your eyes peeled for these young acrobatic insect eaters around your backyard–you may be in the company of our favorite songbird!
This is Robyn Walker-Spencer, and this has been Kachemak Currents. Brought to you by the Center for Alaskan Coastal Studies, which has been connecting you with the nature of Kachemak Bay through education and stewardship for over 40 years.
