Tree Swallows at Broadmoor Wildlife Sanctuary

Posted by Lucy Zipf

“Swallows are more confident and fly nearer to man than most birds.  It may be because they are more protected by the sentiment and superstitions of men.”

Henry David Thoreau, May 20, 1858.

This summer I have been working with Mass Audubon’s Broadmoor Wildlife Sanctuary. With the help of sanctuary director Elissa Landre, I am investigating how climate change is affecting tree swallow nesting behavior, especially the timing of reproduction and clutch size.

Broadmoor’s Wildlife Pond fields dotted with nest boxes

A nest box at Broadmoor

Volunteers at Broadmoor have been monitoring the nest boxes on and off since 1987. There are 55 nest boxes on Broadmoor’s 624 acres, 44 of which were occupied this year by tree swallows.

A tree swallow looks out of a nest box at Broadmoor (Photo by Broadmoor Volunteer Chris Leuchtenburg)

Tree swallow nestlings in a nest box at Broadmoor (Photo by Broadmoor Volunteer Chris Leuchtenburg)

Preliminary analysis indicates that tree swallows are nesting earlier now than in the past, and are nesting earlier in warmer springs. While clutch size has not changed over time, clutch sizes are lower in very rainy years perhaps because there are fewer flying insects to eat.

Volunteer Richard Kent counting tree swallow eggs in a nest box