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Tuesday, April 17, 2012

The three "banded thrushes"

Three sparrows in the genus Zonotrichia have been recorded on Bodega Head.  Zonotrichia means "banded thrush."  Although these sparrows are not true thrushes, the term was used in the past as a more general term for a songbird.  Banded probably refers to their distinctive head stripes.

To tell them apart, look for the overall size, the specific color pattern of black/white/yellow on the head (how many stripes there are, the width of the stripes, the presence/absence of yellow and where the yellow occurs).

Least common is the White-throated Sparrow (Zonotrichia albicollis) — a rare migrant and winter resident on Bodega Head.  I haven't seen one Bodega Head yet, but here's one I photographed in Sebastopol on 16 April 2012 (above).  Note the relatively thin black stripes, the bright yellow lore (between the eye and the bill), and the markedly white throat.

Golden-crowned Sparrows (Zonotrichia atricapilla) are relatively common winter residents on the Bodega Head peninsula (perhaps most common near the village of Salmon Creek, where these photos were taken on 14 April 2012).  The black stripe above the eye is very wide and there is a striking yellow crown (although it's not as bright in mid-winter).

Scientists at the Point Reyes Bird Observatory have recently published an article about migration in Golden-crowned Sparrows.  They used light-level geolocator tags to discover that birds wintering in Bolinas, CA, breed along the coast of the Gulf of Alaska during the summer.   

Here's a description of how the geolocators work: "GLS loggers record ambient light, from which sunset and sunrise times are estimated from thresholds in light curves; latitude is derived from day length, and longitude from the time of local midday with respect to Greenwich Mean Time and Julian day." (Phillips et al. 2004).

To read more about the PRBO study, check out the original article in PLoS ONE.  

White-crowned Sparrows (Zonotrichia leucophrys) are the most common of the three "banded thrushes" on Bodega Head and are the only ones that nest locally.  Note the strong black and white stripes (see below) and the lack of yellow in the lores and on the crown.

ADDENDUM (18 April 2012):

Claudia's comment below spurred me to add a couple of notes about Golden-crowned Sparrows.  You can listen to their three-part song here .  And a fun fact:  There is an interesting association between this song and the California Gold Rush.  Apparently, some miners thought the song sounded like, "No gold here."  See if you think so, too!  

1 comment:

Claudia said...

Yellow and white crowned sparrows are two of those species that are part of my identity and early memories.

My family used to go to Half Moon Bay a few times each summer for an evening picnic. White-crowned sparrow song is the sound of salt spray and hot dogs for me.

The call of the golden crowned sparrow was one that stumped me for months when I first became interested in birds in 7th grade. I'd whistle the song, call them in, but never saw one call. I listened to the entire Peterson bird call record and the only thing that sounded remotely close was the Mountain Chickadee (The full golden crowned sparrow call wasn't on those first recordings). My quest ended when I whistled the call for a person leading a bird watching tour at Bolinas.