Taking the Long View: An inside look at the goings-on at the longest running avian ecology field station west of the Mississippi.

Palomarin Monthly Banding Summary: March-April 2021

This summary was compiled by Point Blue’s Palomarin banding intern Joelle Carbonell with help from Mark Dettling, Banding Supervisor.

Exciting Captures and Observations:

March and April are when breeding begins to take off for the birds at the Palomarin Field Station. Though we are not necessarily trying to nest search during a banding day, we did see some very suspicious behavior from a few of our birds. A pair of Bushtits were excitedly building above one of our nets, quickly expanding their hanging sock-like creation. As they can have up to 8 eggs in a nest, it’s funny to picture all the babies squished inside. Another conspicuous nest builder was the California Scrub-Jay. The pair flew together directly to their nest, right in front of us! One was carrying a comically large stick which it proceeded to tuck into the nest.

During banding, we can see signs of breeding as a physiological difference on the birds. Males can develop a “cloacal protuberance” which is a swelling of the cloaca in order to accomodate an accumulation of sperm. The cloaca returns to its regular size and state once the breeding season is over. Birds that incubate eggs and brood young will develop a “brood patch”. This is a loss of feathers and increased vascularization of the belly area of a bird. It helps increase heat transfer from the adult during incubation to the eggs or nestlings. This typically only occurs on females, but if both sexes incubate, they will both develop a brood patch. Here at Palo, species in which both incubate include woodpeckers and Wrentits. These breeding conditions can allow us to age the bird as an adult since only older birds can breed.

Banding allows us to get detailed information on breeding status that would not normally be available since these conditions are not detectable from afar.

We saw some brood patches in several of our species including woodpeckers, Song Sparrows, and Wilson’s Warblers. We score each brood patch to determine how far along the bird is. Essentially, while the bird is incubating, its brood patch looks different from when it was just beginning to lose its belly feathers and this can convey important information about the timing of breeding. We caught three birds with the “greatest” development of their brood patches indicating they probably already had eggs! For birds we suspect are incubating, we make sure to return them to the site of capture so they are as close as possible to their nests as we can get them.

Let’s Do the Numbers:

In 28 days (2,953 net hours) of mist-netting at Palomarin in March and April, we captured 93 new birds and recaptured 107 previously banded birds. A total of 198 birds of 26 species were caught. Approximately 7 birds were caught per banding day.

At our other West Marin banding sites, we captured 88 new birds and recaptured 44 previously banded birds. A total of 140 birds of 27 species were caught over 12 banding days in March (455.75 net hours), an average of approximately 12 birds per day.

The highest capture rates at Palomarin were on March 24th at Palomarin with 12 birds and April 14th with 17 birds. At our other West Marin banding sites, the highest capture days were March 19th and 27th with 25 captures each, both at Pine Gulch (in the Bolinas Lagoon Open Space Preserve).

At Palomarin, the following species were caught in the highest numbers: Wilson’s Warbler (32), Song Sparrow (25), Oregon Junco (15), Hermit Thrush (13), Orange-crowned Warbler (12), Chestnut-backed Chickadee (11).

Across all off-sites (March only), the highest numbers of captures by species were: Song Sparrow (22), Pine Siskin (18), “Myrtle” Yellow-rumped Warbler (15), Hermit Thrush (13), and Common Yellowthroat (10).

A young Sharp-shinned Hawk. We know it is young because of the streaks on the chest, the rufous tips of its feathers, and its yellow eye color since adults have red eyes. Photo by Joelle Carbonell.


This Savannah Sparrow from our banding site at Pine Gulch (Bolinas Lagoon Open Space Preserve) was an unusual catch for Point Blue. In the last 10 years, we have only caught 11! Photo by Joelle Carbonell.


An adult Pacific Wren. Although you cannot tell from the picture, this little bird has a big song. Photo by Joelle Carbonell.


A Chestnut-backed Chickadee posing for the camera. Photo by Joelle Carbonell.


About these Summaries:

Point Blue interns and staff at our Palomarin Field Station share these blog posts in an effort to further engage the public in our science. We are grateful to our partners at the Point Reyes National Seashore and to our surrounding Bolinas and West Marin County community for their support of our work.