[SBB] Morgan Hill hummingbirds

["Steve and Heather Rottenborn" <[[email protected]]>]

South Bay Birders,

In addition to large numbers of Anna's Hummingbirds, we have had 
unexpectedly high numbers of Selasphorus (Rufous/Allen's) hummingbirds at 
our house, on the east side of Morgan Hill west of Anderson Reservoir, over 
the past couple of weeks.  On the evening of 22 August, in an attempt to 
estimate the number of different individuals that might be present, I 
recorded 35 minutes of video of hummingbirds (focusing on Selasphorus) at a 
single feeder over a 2-hour period.  After many hours of downloading stills 
and comparing plumages of different birds, I was able to determine that at 
least 42 different Rufous/Allen's hummingbirds visited that single feeder at 
our house that evening.

Differences in the pattern of the throat (presence/absence, extent, and 
location of red feathering as well as density and size of dark spotting on 
the chin and throat), auriculars, and tail, and on some individuals the 
extent of rufous in the uppertail coverts or unique patterns of rufous in 
the auricular/lateral crown area, allowed for distinction of many 
individuals in the video.  Given that many other individuals (particularly 
apparent immature females) appear virtually identical, and that I was able 
to get decent video (attempting to get the throat and tail on as many birds 
as possible) of only a subset of the birds present, the actual number of 
different Rufous/Allen's Hummingbirds present that evening must have been 
60+.

I attempted to identify, at least tentatively, as many of the Selasphorus to 
species as possible, based largely on the width of the outermost rectrices 
(and on some, presence of emargination on R2) visible in the video stills. 
Of the 42 different individuals, I suspected that 23 were likely Rufous and 
2 likely Allen's; I was not able to see enough on the tails of the other 17 
to even guess at their identity.  Of course, without the birds in the hand, 
ID of these birds even from video stills must be considered tentative, 
although one Allen's with very narrow rectrices, and many of the Rufous with 
broader rectrices, were almost certainly identified correctly.

For what it's worth, the maximum number of Selasphorus I saw in the yard 
simultaneously that evening was 10-15, and most of the time, no more than 
4-6 were present -- this indicates how difficult it would be to estimate 
abundance of these birds at a given location on a single day without such a 
detailed comparison of images.

Two immature Black-chinned Hummingbirds were also present in our yard on 
both the 22nd and 23rd.  We've had a different immature over the past few 
days, and this evening three Black-chins were present -- two 
immature/female-types and an adult male, the first of those we've had in the 
yard.

Good birding,

Steve Rottenborn
Morgan Hill, CA 


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