[ Follow Ups ] [ Post Followup ] [ TAS BirdBoard ] [ FAQ ]
Posted by Bill Pranty on 19:40:53 11/28/14
In Reply to: Re: Tropcial Kingbird and more- much more posted by Robin Diaz
Good evening Robin and others,
I can _help_ answer the question.
In 1979, Melvin Traylor had published in _Auk_ a paper that showed differences between populations of Tropical Kingbirds. This paper caused the AOU to split out Couch's Kingbird as a species distinct from Tropical Kingbird.
In adult kingbirds, P8 is the longest primary feather. Traylor devised a "wing tip index" that was derived by dividing the difference between P8 and P5 by the difference between P8 and P10. This ratio was then compared to a second ratio, that dividing bill length by wing length.
The use of ratios rather than individual measurements helped prevent a single aberrant feather (abnormally long or short, or maybe damaged) of aberrant bill from causing a misidentification.
When compared, these two ratios allowed for identification to be nearly 100% diagnostic between ADULTS of the two species. These same ratios showed no distinguishable differences between the species for JUVENILES.
Vocalizations, of course, do not differ within a species by age, and so are diagnostic between species is audio recorded. (But note that one kingbird along the Broward/Palm Beach county line in 1996 was identified as a Couch's Kingbird by call notes but then was later salvaged and determined to be a Tropical Kingbird by measurements. Also, a second kingbird -- this one in Miami-Dade County in 2001 -- was identified by some observers as a Couch's Kingbird, and by other observers as a Tropical Kingbird, by vocalizations heard.).
Traylor's paper is available at the link below.
Best regards,
Bill Pranty
Bayonet Point, Florida
[ Follow Ups ] [ Post Followup ] [ TAS BirdBoard ] [ FAQ ]