East Coast Bird Makes Rare Appearance in Mist Net: August 13, 2022 Zuma Canyon Banding Cycle

Above: The wing of a Rose-breasted Grosbeak, photo © Walt Sakai

Start at 6:15am, closing at 12:15 pm
Total 20 nets up
Total 55 birds, 16 species

• 2 Allen’s Hummingbirds (Selasphorus sasin)
• 2 Ash-throated Flycatchers (Myiarchus cinerascens)
• 1 Pacific-slope Flycatcher (Empidonax difficilis)
• 1 California Scrub-jay (Aphelocoma californica)
• 1 Purple Finch (Haemorhous purpureus)
• 5 House Finches (Haemorhous mexicanus)
• 2 Song Sparrows (Melospiza melodia)
• 3 Spotted Towhees (Pipilo maculatus)
• 4 California Towhees (Melozone crissalis)
• 1 Rose-breasted Grosbeak (Pheucticus ludovicianus)
• 3 Orange-crowned Warblers (Leiothlypis celata)
• 11 Common Yellowthroats (Geothlypis trichas)
• 1 Bewick’s Wren (Thryomanes bewickii)
• 2 House Wrens (Troglodytes aedon)
• 5 Wrentits (Chamaea fasciata)
• 11 Bushtits (Psaltriparus minimus)

Wow! It’s been a while since I last did a blog post about a Zuma Bird Banding cycle, the last being for May 21. Here are a couple updates before I get into the cycle on August 13.

• One net that was previously near some picnic tables has been relocated next to some slightly dense shrubbery near the banding station (net 12 became net 28). Another net near a water feature was rotated 90º so that trees become the backdrop (net 26). Both nets are doing great!!
• We’ve been catching a very good number of birds considering the summer weather and last year’s numbers at this time (over 10 birds if we were lucky). We’ve been consistently getting numbers in the 40s and 50s.
• Migratory birds that arrived in the spring spent their summers at Zuma as expected, including Hooded and Bullock’s Orioles, Black-headed Grosbeaks, and Black-chinned Hummingbirds. Each of these species have began migrating to their wintering grounds and are no longer being caught in nets. Ash-throated Flycatchers that arrived a little later are still around though!
• We await the fall migrants like White-crowned Sparrows and Yellow-rumped Warblers who will likely be showing up within the next month!
• We saw lots of breeding birds in the early spring and summer. Now, we’re banding many of their offspring (Hatch Year birds).
• Last summer, the habitat at Zuma was really dry. While vegetation started to die back in June this year, the area is still quite green! The number of birds we have been catching has seem unfazed!

August 13th Cycle

Okay, now you’re pretty up to date with what’s up at Zuma. This cycle began at 6:15am, which, believe it or not, is quite late compared to what we were having to deal with earlier in the year as we head into long winters. I actually got a somewhat decent amount of sleep! The weather in the morning was cool, but cloud cover was absent. As an hour passed, the temperature began to warm and more birds started moving about and getting caught in nets.

By the first net round (when we go to check nets), we were already bringing back a very good number of birds with a good diversity among species. While checking one net, one of my mentors and I found ourselves with around seven Bushtits! Bushtits are known to travel in family groups, sometimes containing as many as 20 individuals. Every so often, we have a good chunk of a meandering family group fly into a single net. The bander is then tasked with meticulously removing each one, which must be done as swiftly and efficiently as possible as Bushtits have a tendency of stressing easily. We like to joke at the banding station that if someone’s taking a long time to come back from a net round that they got a flock of Bushtits!

My mentor and I removed each Bushtit as well as a few Orange-crowned Warblers who are arriving on the fall migration. Very fun! We moved onto the next few nets and brought back to the station what must have been close to 15 birds in total. While walking back, we heard on the radio that one of the banders had caught a Rose-breasted Grosbeak in one of the nets, an East Coast bird that’s been reported at Zuma for a few weeks now.

It was back in late June that the first eBird checklist made mention of a Rose-breasted Grosbeak at Zuma Canyon. At the time, a few birders had only heard the bird singing and hadn’t actually gotten any photographic evidence of the individual. The report was also mildly unconvincing as 1) Rose-breasted Grosbeaks aren’t at all from around here, and 2) the calls are near identical to those of the Black-headed Grosbeak, a common bird spending the summer here in SoCal. We joked about the bird at the banding station: “It would be pretty funny if we actually caught the bird!”

Practically right after that initial report of the grosbeak, birders in the LA area flocked to Zuma in search of the individual. Within a few days, the bird had been photographed and the image was included with an eBird checklist. So there it was, a Rose-breasted Grosbeak at Zuma Canyon! The Rose-breasted Grosbeak (Pheucticus ludovicianus) is a long distance migrant completing a journey from Canada, through the U.S., to Central and northern South America. As seen in the range map below, they stick to the eastern half of North America, but not all will obey this pattern. According to Kimball Garrett, a prominent birder in SoCal and retired ornithologist with the Natural History Museum of Los Angeles County, around 20 or so Rose-breasted Grosbeaks will make their way to the LA Basin annually, much to the bird’s mistake.

Back at the banding station, everyone was swiftly processing the birds that were coming in. Bushtits, California Towhees, and Common Yellowthroats were being processed left and right. I banded a Hatch Year (HY) finch, the bird still with some downy feathers sticking out of the head. Since we were so busy, I had took one look at the individual and identified it as a House Finch. I recorded the data, took two quick photos, and reported it to the master bander. I let the bird go. Later while going through the photos and uploading them to iNaturalist, I realized I had made a mistake with the ID. The beak of the bird was pointed, quite different from that of a House Finch (they have stocky beaks). Had I actually banded a Purple Finch without realizing it?! I quickly emailed the rest of the banders proposing the new ID. The master bander got back to me explaining that the photos weren’t super clear, but that based on a few details, I had indeed banded a Purple Finch. In the 28 year history of the Zuma bird banding station, only 100 Purple Finches have ever been banded compared to 1,200 House Finches. Have any other Purple Finches been misidentified as the more common House Finch?

At first glance, Purple Finches and House Finches can look remarkably similar. Notable differences include the House Finch’s shorter, more rounded bill, long rounded tail, and slender body shape. Purple Finches on the other hand have thick, pointed bills, a notched tail, and streaked under tail coverts that are visible when the bird is in the hand. It should be noted that the western subspecies of the Purple Finch (Haemorhous purpureus californicus) does look much more similar to House Finches when compared to the eastern subspecies (H. p. purpureus).

After the Rose-breasted Grosbeak was processed, the immature male was put in a bird bag to await a highly anticipated photo shoot. Half of the bird looked very similar to an adult female/young male Black-headed Grosbeak, with a brown head, tawny cinnamon breast, and light streaking across the body. But the other half pointed to the Rose-breasted, with bold black and white primaries and light red feathers in the inside of the wing and at the chest. The bird was stunning. Moreover, the bird that had been photographed and uploaded to eBird was an adult male. There must be more that one of these grosbeaks residing at Zuma!!

This next photo documents a molt limit in the right wing of the Rose-breasted Grosbeak. A molt limit is the observable difference in feather wear and color that is crucial in aging a birds. The photo reveals a molt limit among the primaries and secondaries of the bird’s wing. The secondaries here are brown and rather abraded, suggesting they are older. The primaries are black and fresh, suggesting the bird has already molted them. Along with the with the flight feathers are the coverts protecting their bases. You can see the coverts corresponding to the old secondaries are relatively abraded as well.

And on the topic of molt, many of the Bushtits (Psaltriparus minimus) we were getting were molting their flight feathers as well as they begin to undergo their complete molts. Take this example shown in the photo below. The fifth primary is just growing in. This is what we banders term “flight feather molt” since a flight feather (primaries, secondaries, and tertials) are well, molting aka growing!

Additionally, we see that the secondaries are a lighter shade of brown than the primaries, suggesting they are older. As sun hits feathers, they gradually become lighter and lighter. Generally, the secondaries and tertials are the feathers receiving the most light, so they bleach the easiest. Additionally, when birds first grow their feathers when they are young, color is an expensive commodity. This is why the feathers in young birds are usually duller in color. When the bird molts their feathers when they’re older, nutrients that produce color are more available in the bird’s diets, so they can have darker, more bold colors.

And because we’re ALL about molt in bird banding, here’s yet another example. Now, this might just be the coolest thing I’ve seen! I present to you a Hatch Year (HY) Spotted Towhee (Pipilo maculatus)! When these towhees are young, they are super streaky and predominantly made up of varying shades of brown. Essentially, good camouflage that can sometimes require a little more thought when identifying an individual bird. Seriously, like who would think that’s a Spotted Towhee?!

The Spotted Towhee was transitioning from the juvenile plumage to plumage more closely resembling that of a non-juvenile bird. I say non-juvenile because the black, orange, and white feathers can be seen in Hatch Year and After Hatch Year birds. Spotted Towhees will be brown and streaky for a few weeks after hatching according to Birds of the World and then will promptly molt afterwards to the fancy colorful feathers.

The Hatch Year female I banded had the characteristic black, orange, and white breast with a fine streak of juvenile feathers going down the middle. The head was still brown like a juvenile’s. The wings reveled a similar deal with the brown feathers (juvenile) and black feathers (older bird) representing a molt limit. The back and coverts too were more lightly colored than the rest of the body. And… there were even growth bars on the upper tail coverts! The upper tail coverts!! Okay, I’m kinda nerding out now with this bird! Deal with it, you’re the one that clicked this blog post! 😉

In total, the day brought many good birds representing 16 species! That’s all for now, so stay tuned!