[cobirds] Juvenile Spizella Sparrow ID

This is a good time of year to bone up on juvenile sparrows in the genus Spizella.  The two common species we have in this genus in CO at this time of year are Chipping and Brewers.  Field Sparrow juveniles could be found in very limited numbers now on the far eastern plains and Clay-colored Sparrows, despite some tantalizing summer records from North Park, are not known to nest in CO.  Juvenile Clay-colored Sparrows would not be expected here until late summer-autumn.  American Tree Sparrow doesn't show up until November and Black-chinned Sparrow has only bred for a few years that we know of very locally in extreme w or sw CO.

The rest of this post deals with separating the two Spizella sparrows that are common and expected in many low elevation areas now or very soon (when Chipping Sparrows from the lower mountains disperse eastward as part of their molt migration).

This post was sparked by seeing a family group of Brewer's Sparrows within the Cottonwood Hollow/Running Deer Natural Areas complex today on the east side of the Poudre River south of Prospect in Fort Collins (Larimer).  This was somewhat surprising to me but I suppose the abundance of rubber rabbitbrush in this area is suitable breeding habitat.  I just have not known them to breed in this place I have visited on a fairly regular basis over the past several years.

         

So, the bird on the left is a juvenile Chipping Sparrow.  The one on the right is a juvenile Brewer's Sparrow.  Best separating feature would be to see what kind of adult sparrows they are hanging out with.  I watched the Chipper being fed at Grandview Cemetery a few years ago by an adult Chipper.  The juvie Brewer's today was with two siblings and an adult Brewer's.  Second best separator would be the rump color: gray in Chipping, tan in Brewer's.  Can't see this feature in these pics.  Next best thing is perhaps the lores area.  Black line from eye to base of beak in Chipping, pale in Brewer's.  Eyering is supposedly broken in Chipping and complete in Brewer's.  I can see broken in Chipping here but tough to call that of the Brewer's shown here "complete".  Eyeline behind eye is supposedly darker in Chipping than that of Brewer's.  These look about the same in terms of darkness, but with Chipping being black and Brewer's brown.  Tail length is tough but Brewer's is typically a little longer, which I think shows here.  This would not be a stand-alone character, but maybe would supplement suspicions garnered from other characters. 

Bird identification seems to be getting more clinical all the time, especially the more we graphically depict vocalizations, but I'd like to think it will always be part art.  The views shown were selected from hundreds of photos.  In the field we normally don't get views this good and close-up, and we don't get the candidate species posing the same direction next to each other.  That's why it's quite OK to say "sparrow sp.", often.  But, if we get good views, and can get photos to enlarge in the comfort of the living room, IDs of some individuals are possible.

Dave Leatherman

Fort Collins