Point Blue Conservation Science: Monthly Banding Summary, January 2019
March 18, 2019
This summary was compiled by Point Blue’s Palomarin banding interns Sarah Fensore and Nick Liadis with help from Mark Dettling, Banding Supervisor.
About Point Blue: Our mission is to conserve birds, other wildlife, and ecosystems through science, partnerships, and outreach.
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Exciting Captures and Observations:
The birds came in pairs this month! It’s always a nice surprise when you get two of the same species in a net together. For banders, it’s more than just a nice coincidence. It creates an opportunity to compare plumage variation within a species, which can be useful in telling the age or sex of certain birds.
Some of the guides that we use to help determine the age and sex birds describe these plumage variations. The variations can be difficult to contextualize, however, without seeing the range of possibilities in person, for example with plumage color.
Take the American Robins pictured. Although both birds have rufous on their breast feathers, the bird on the right shows a greater extent of that color. It’s richer in saturation, too, which points to the bird being a male. In comparison, the individual on the left shows a muted variation of the color, pointing towards it being female. The descriptions of the variation in rufous we have in our guide to aging and sexing birds becomes clearer when comparing the two birds side by side.
Also notable is the amount of black feathers in the head of these birds. The lack of them in the left-hand robin makes it most likely a female, while the other, with its dark black head, is a male. It’s not always this easy though, as many individuals can be in the middle of this spectrum, with the age of the bird also contributing to variation.
The comparison helps us to see characteristics within the plumage that might be difficult to describe with words. We did this with other species that came in pairs, too. Two birds are better than one!
Pictured here are two Varied Thrushes caught in a net together. Based on the information about the plumage characteristics of the American Robins, can you guess which bird is male and which is female? Seeing these two birds next to each other helps provide a basis for comparing the color of the other—the bird on the right is female due to the relatively brown head and muted rufous, while the bird on the left is male, with dark black feathers and rich rufous tones.
These two Townsend’s Warblers are both males, but one is a young bird while the other is an adult. Among other features, we look at the completeness of the black markings on this species. The pattern on the face of the bird on the left has more complete areas of black while the younger bird on the right has mottled black feathers. We can confirm similar variations in the amount of black by looking at the throat feathers of these birds as well. Black feathers are one criteria that we use to help us determine the age and sex of Townsend’s Warblers.
The difference in the crown pattern of these two Golden-crowned Sparrows is striking. The bird on the left is showing a bright adult plumage with bolder black stripes and an obvious yellow crown. The bird on the right shows a more indistinct pattern, which is characteristic of a younger bird. These two birds show crown patterns toward opposite ends of the spectrum, but there are many individuals that fall in between for which we cannot determine the age.
Let’s Do the Numbers:
In 13 days (1346.5 net hours) of mist-netting at Palomarin in January, we captured 122 new birds and recaptured 100 previously banded birds. A total of 222 birds of 23 species were caught. Approximately 17 birds were caught per banding day.
At our other West Marin banding site, we captured 46 new birds and recaptured 41 previously banded birds. A total of 87 birds of 17 species were caught over 4 banding days in January (208.84 net hours), an average of approximately 23 birds per day.
The highest capture rates at Palomarin and our other West Marin banding site were on January 17th at Palomarin with 39 birds and January 10th at Pine Gulch with 29 birds.
At Palomarin the highest numbers were captured for the following species: Ruby-crowned Kinglet (113), Townsend’s Warbler (32), Hermit Thrush (13), Oregon Junco (10), and Fox Sparrow (7).
At the off-site, the highest numbers of captures by species were: Ruby-crowned Kinglet (25), Song Sparrow (13), Hermit Thrush (12), Bushtit (8), and Golden-crowned Sparrow (8).
About these Summaries:
In an effort to share our science with the public, Point Blue interns and staff at our Palomarin Field Station (Palomarin or “Palo”) in Point Reyes National Seashore near Bolinas, CA produce these monthly bird-banding summaries. Our science interns create these summaries as part of their science outreach training.
Our Palomarin Field Station is open to the public. Consider visiting us! Learn how by visiting our mist-netting demonstrations web page.