Audubon’s Yellow-rumped Warbler - sunshine in winter!

December 5, 2006 on 8:50 pm | In Daily Local Birder |

Greetings!
Just as nature sees fit to hand out Vitamin C-packed lemons in the darkest days of the year, the Yellow-rumped Warbler bursts like a dart of sunlight through the winter birdwatching scene in Sonoma County, California. This special bird is, in fact, one of the only warblers commonly seen in the western United States in this season.

Yet again, my apple tree, visible right now from where I type, is playing host to this tiny, active bird. My birding field guide says he can reach 6″ in length, but it appears to me that our local variety is about an inch smaller than this. As I mentioned in an earlier post, a single Yellow-rumped Warbler appears to have been drawn here by the presence of a Red-breasted Sapsucker. The sapsucker drills holes in the tree, and the moment he leaves, the warbler appears to glean anything the bigger bird may have left behind in the excavations. The Yellow-rumped Warbler is the first bird I am seeing when I arise, and he is the last one to go to bed after sunset. All of the time in between is spent in flitting between the roof of my home office and the branches of the Gravenstein.

Field notes on the Yellow-rumped Warbler
There are marked visual differences between immature, male and female birds of this species. In general, the mature male shows more black both on the face and breast. His throat is canary yellow - what a sight! And his head and underwing are also gilded with this sunny tone. I have read that he changes to a duller set of colors in winter, but as winter is as yet the only season during which I have observed this bird, I cannot conceive of how bright they would be during the breeding season. The female shows more striping and less white on the underbelly than the male. However, when seen from behind, alighting on a tree, both sexes display the yellow rump from which they derive their name. Both sexes also feature a white eye ring and various white wing markings.

I have now been fortunate enough to study these warbler wonders in several locations. To date, my most unusual identification was of an extremely small individual living in a redwood grove in Jack London State Park. Exactly like a nuthatch, he was going up the completely vertical side of an evergreen, clinging to a dense bed of emerald green moss. The color palette in the gloaming of the cold wood was unforgettable! I have observed tree-clinging behavior here at home, too, though not on anything quite so straight up-and-down.

For those of you wishing to identify your first Yellow-rumped warbler, I have created a sketch here which includes both male and female birds, as well as the Ruby-crowned Kinglet:

Because the Ruby-crowned Kinglet is also a small greyish bird with yellow trimmings, you might feel some concern at distinguishing the two. Here is a list of markings that will help you set the two little birds apart, especially if you see them both in the same location, as we do.

Yellow-rumped Warbler
Yellow on throat, not belly
Yellow on male’s crown
Female has striping
Larger than Ruby-crowned Kinglet
Yellow on rump
Bright white under rump

Ruby-crowned Kinglet
Even smaller than Yellow-rumped
Yellow relatively pale and diffused over belly
Extremely large, prominent white eye ring (larger than warbler’s)
Ruby-red patch on crown (only visible in the right light)

Study my sketch to memorize the various field marks that distinguish these birds, and winter identification should be no problem, even for a new birder. Though I do not have a surefire location for you to view this bird, this Jack London State Park bird watching map does show where I saw the dainty individual in the moss, and as Yellow-rumped warblers appear to become creatures of habit where the feeding is good, I wouldn’t be surprised if that bird is still there this week. Do approach him slowly and quietly. He is slightly shy.

The Yellow-rumped warbler is a fairly vocal bird, and sings in flight. Chwit, ssit and other abrupt chirpings are its common sounds. I have observed that it is silent around its feeding area on the tree (perhaps because it is afraid the sapsucker will hear it and come chase it away again). By the same token, it is very territorial and is able to get the best of both the Ruby-crowned Kinglet, and any House Finch bold enough to attempt investigating the sapsucker holes. I’ve seen some alarming dust-ups this week between these small, pretty birds and so far, the warbler always wins.

Further notes on this Sonoma County warbler
It’s important to clarify a bit of confusion that came about when it was decided that both Audubon’s and the Myrtle Warblers would be re-classified under the general name “Yellow-rumped”. The Myrtle Warbler is uncommon in the west, and features dark cheeks, and a white throat in the male bird. Though these two birds were once considered different species, they are now lumped together.

They Yellow-rumped Warbler prefers a conifer tree as a nesting site, where it creates a feather-lined cup. 4-5 white, speckled eggs are lain. Flocks break up in the winter, and this would explain why I have never had the chance to view more than 2 of these birds at a time. I would be most interested in comments from anyone who has gotten to study flocking behavior in these active birds.

This winter, I have become even fonder of the Yellow-rumped Warbler, after many, many days of gazing at him. He is as spry as a cricket and as cheery as a dear friend. May this winter bring you the pleasure of warblers to brighten your December.