Larry, thanks for sharing Bruce Peterjohn's notes. As a relatively new bird
watcher, I find reading notes laying out how a species is being identified to
be fascinating and instructive.
Sent from my iPhone
On Nov 30, 2012, at 3:24 PM, Larry Meade <uberlarry@xxxxxxx> wrote:
Here are Bruce Peterjohn's notes about the hummingbird.
Identification of the Green Spring GardensPark Rufous Hummingbird
Theextensive rufous at the base of the tail indicated that it was a
hummingbirdof the genus Selasphorus. Calliope hummingbird was eliminated
bythe more extensive rufous in the base of the tail on this bird, its
overalllarger size (especially bill and wing length), and the shape of its
centraltail feathers (distinctly wedge-shaped in Calliope but not on this
bird).Broad-tailed Hummingbird is a larger bird than Rufous/Allen's and the
measurementsof the bill, wing, and tail were all too short for a Broad-tailed
(forexample, the tail was only 25 mm long while most Broad-taileds have
tailsgreater than 30 mm long).
Thefinal identification challenge was the separation of Rufous from
Allen'shummingbirds. First, we have to determine the age and gender of the
bird.This bird was sexed as a female based on the extensive green base to
thecentral tail feathers (males have an extensive rufous base to these
feathers).She was aged as a hatch-year bird based on the presence of grooving
onher mandible (a feature found on hatch-year birds but is lost during
theirfirst year so that these grooves are not normally present on adult
birds).Establishing that the bird was a hatch-year female allowed us to use
severalmeasurements to establish this identification. Allen's is overall a
slightlysmaller bird than Rufous, size differences that are not evident in
thefield but can be confirmed in the hand. All of the dimensions of this
birdwere well within normal for a Rufous but were either at the extreme endor
entirely too large for an Allen's. For example, the wing length wasgreater
than 44 mm while hatc
h-year female Allen's have wing lengths lessthan 43 mm (and normally around
40 mm). The outermost tail feather wasalso relatively wide at 4.7 mm, while
the width of this feather on hatch-yearfemale Allen's is 3.3 mm or less.
Given that all of the measurements stronglysupported the identification of a
Rufous Hummingbird, I did not feel theneed to collect any feathers for
documentation purposes (and I am not surethat the permit issued by the park
would have allowed me to collect feathers).
Thesecond tail feather lacked any apparent emarginations on this bird,
whichfrom my experience occurs very frequently on hatch-year female Rufous
Hummingbirdsas well as on Allen's Hummingbirds. When this feather is
distinctly emarginated,then that feature is distinctive for a Rufous.
However, many Rufous lackthese emarginations while some Allen's can have
slightly emarginated feathers,so use of this feature requires some experience
with both species to understandthe range in variation found in both. Based on
our study of birds in thehand with proven identifications, the color of the
feathers around theeye is not a reliable field mark and should not be used in
the separationof these species.
Bruce Peterjohn
Laurel, MD
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