Zuma Canyon Recoveries

By Walter Sakai

Walter-Sakai-Zuma-Canyon-Bird-Banding

Walter Sakai, Zuma Canyon Bird Banding

I’ve been banding birds in Zuma Canyon in the Santa Monica Mountains for 18+ years now. We use 12 m long x 2.8 m high with a 30 mm mesh mist nets stretched out using standard EMT poles to capture the birds. We place uniquely numbered aluminum “bracelets” or bands (or “rings” in Europe) around their leg, and take some physiological measurements. The protocol has changed somewhat over the years. At present we band every two weeks from sunrise for six hours, using 10 to 20 nets depending upon the personnel, all of which are volunteers.

One of the questions I always get is “what have you learned?”

As it relates to birding, one of the vexing problems/questions that birders have is “Is that the same bird I saw five minutes ago?” Last month? Last year? Back in 1998, I was excited to see my first Northern Waterthrush, an uncommon neotropic migrant, in the riparian area of Zuma Creek at the mouth of Zuma Canyon. Fortunately, I had mist nets up in the area, caught the bird, and banded it. In fact, I banded two waterthrushes that morning. Then, the following spring, I banded my third waterthrush, now a ho-hum bird for me.

The following fall (1999) I saw a Northern Waterthrush, and it had a band! Was it mine? Not wanting to get overly excited, I rationalized that this was a different bird banded by another bird bander. As luck would have it, I caught this bird, and it was one of the three birds I banded the year before. Then, in the fall of 2000, I caught this bird again! (Yawn now.) The National Geographic field guide shows that this bird migrates predominantly east of the Rockies, so this bird was probably making the “wrong turn” every year and migrating down the Pacific coast.

A corollary to this is that I caught the bird on 12 Sep 1998, recaptured it on 25 Sep 1998, and 30 Jan 1999. This and the other waterthrushes likely spent the winter at Zuma marsh. The next winter I captured it on 4 Mar 2000. During the third winter, I captured the bird on 23 & 30 Dec 2000 and on 1 Mar 2001. I believe I “saw” the bird at other times, but I haven’t had a chance to go back to check my 15 year old field notes. So we now have some good evidence that the waterthrushes may spend the entire winter at the mouth of Zuma Canyon. Or maybe they did continue south. On their spring migration, they again stopped at the mouth of Zuma Canyon.

The icing on the cake would have been if I caught this same bird when I was banding birds in Costa Rica, but alas, no such luck.

Not counting the same bird becomes critical when one is doing point counts or the annual Christmas bird counts. To some extent, bird banding addresses these questions. Once the bird is caught and an aluminum band is placed on its leg, when the bird is caught again, we know when and where it was originally banded. Of course, one has to catch the bird again! No easy task, since we catch these birds passively with mist nets.

At Zuma Canyon (about a mile inland from the mouth of Zuma Creek), a little over 20% of the birds we capture are recaptures, birds that were banded previously. The high percentage is mostly due to the fact that we have a large number of year round resident birds (e.g. Wrentits, Bushtits, Song Sparrows, California and Spotted Towhees, and California Thrashers). Yet I also noted over the years but never analyzed was the number of migrants that seem to return to Zuma Canyon each year.

Spotted-towee-by-walter-sakai

Spotted Towee, Photo by Walter Sakai

Now this is not particularly earth-shattering, as researchers have noted this for centuries, and even John J. Audubon famously tied a gold thread around the leg of a phoebe and noted its return the following spring. Raptors are known to use the same nest year after year, and colonial birds return to the same nesting grounds each year.

What I thought I’d focus on are the migrant passerines, specifically the wintering birds. Recaptures of these small passerines are on the order of fractions of a percentage, and what is interesting is that these birds breed north in Canada and Alaska, returning each year.

Let’s look at Audubon’s Warblers, our most common migrant wood warbler. We’ve banded 964 Audubon’s Warblers at Zuma Canyon from 1995-2012. We have recaptured 135 birds, but a majority of these recaptures were caught during the same winter or multiple times in a season. This leaves us with 50 birds that were banded one winter and were captured during a successive winter. Half were recaptured during the following winter and were never seen again (see table). There have been 11 birds caught two years later, 4 were caught three years later, 2 were caught four years later, 6 were caught five years later, and 2 were caught six years later. These 50 birds account for 5.2% of the birds banded.

We also capture a fair number of Hermit Thrushes and have banded 673 birds during the same period of time. There were 42 birds (or 6.2% of the birds banded) that were banded one winter and were captured during a successive winter. Unlike the Audubon’s Warbler, the majority of birds were recaptured two and three years after banding. Yet the Hermit Thrushes were our longest returning birds, as there was a bird returning for the 8th year and three others for their 7th year. The 8th year bird was captured at Zuma during five different years, the 1st, 2nd, 3rd, 7th and 8th after banding.

Hermit-thrush-by-walter-sakai

Hermit Thrush, Photo by Walter Sakai

A third example is the Golden-crowned Sparrow. We banded 263 birds during the same time period. There were 78 recaptures. There are 28 birds that were banded one winter and recaptured during a successive winter. These 28 birds are 13% of the birds we have banded, a surprisingly large number. A majority of these birds were captured within two years after banding. The oldest bird was 5 years.

A fourth example is the Black-headed Grosbeak, a summer breeder at Zuma. We banded 299 birds from 1995-2012. There were 36 recaptures, with 16 birds (5.4%) that were banded one summer and were recaptured during a successive summer. With the exception of one bird captured seven summers later, the rest were recaptured within three summers.

black-headed-grosbeak-by-walter-sakai

Black-headed Grosbeak, Photo by Walter Sakai

Last, as a contrast, there is the Gambel’s White-crowned Sparrows. These birds were banded at the University of California’s Burns Pinon Ridge Reserve, a high desert site near Yucca Valley, CA. Since 1990, we banded 835 birds with 118 recaptured. Counting only those birds banded one winter and captured during a successive winter, we have 29 birds. The longest lived bird was three years after banding. At this site, banding occurred just twice a year, in the spring and late fall. At a minimum, this is just two weekends a year, although for a number of years, we banded for an entire week in the spring. So the fact that we recapture these birds during two tiny windows during the year is amazing.

What brings these birds back to the same locale? If a bird survives a winter, avoids predators, and gains enough fat for the spring migration in a particular area, at least anthropomorphically, it would seem wise to return to that area. Why try somewhere else? Why not go back to that creek in the Eastern Sierra that you caught your limit of trout every morning! So these findings should not be particularly surprising.

For some of our larger bird examples the answer is more obvious. Raptors return to the same cliff face or large tree, as there are limited numbers of “good” nest sites. Terns return to the same nesting colonies in marshes or on sandy beaches, as these locales possess species specific resources for the birds and are increasingly rare.

On the other hand, Zuma Canyon looks like any other canyon in the Santa Monica Mountains, be it Big Sycamore Canyon, Solstice Canyon, Temescal Canyon, or . . . All are south facing canyons draining into the Pacific, and the vegetation is pretty much the same. The only obvious difference that comes to mind is the presence and amount of surface water. So why Zuma Canyon? Now, it could very well be that these birds are moving back and forth from one canyon to the next. I don’t have the resources to check this. The only banding I have done outside of Zuma Canyon is seven breeding seasons in Solstice Canyon, and we have never had a bird cross from one canyon to the other.

Each finding leads to more questions, so we continue to band every two weeks.

Originally published in Western Tanager Vol.80 No. 1 Sept/Oct 2013

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