[texbirds] COTE vs FOTE bill tip color an overlapping trait

From: MBB22222@xxxxxxx
To: texbirds@xxxxxxxxxxxxx
Date: Fri, 7 Dec 2012 13:43:51 -0500 (EST)
COTE vs. FOTE - bill tip color - an overlapping trait 
 
First I want to say thank you for so many nice comments I received about my 
 illustrations showing differences between Common and Forsterâs Terns 
during fall  (November). Especially one comment that somebody plan to print my 
illustrations  and stick them to the field guide (especially that this one 
came from very  experienced birder) was both encouraging for putting together 
plumage analyses  from other times of the year and good âpayâ for my 
initial 
effort.  
 
Interestedly today I received a couple email from people asking me what  
about yellow COTE bill tip that I assumed from text COTE has and FOTE does 
not.  Well, I already mention that I left bill alone as for example length and 
shape  discussed in some guides are traits that overlap so I do not see them 
as useful  traits, especially in the field. Perhaps as you will see in 
uploaded new  illustration COTE might has on average larger yellowish tip this 
time of the  year than FOTE and might has it on average showing more often 
but this trait is  also overlapping so I do not see it useful as well. To 
notice and try to analyze  end of the tip is also in most cases impractical (if 
not impossible) and only  very good photos, sharp and taken from very close 
distance might allow to see  it. I do not know many people who try to 
photograph every COTE and FOTE they see  so trying to compare this trait in 
both 
species might be inadequate. When  looking at single tern from not too close 
distance judging the size of yellowish  tip - well good luck. Again because 
there is overlap I would rather tried to  concentrate in the field on 
important traits as very often we do not have too  much time when observing an 
individual quickly passing by. 
 
Here is quickly put together illustration showing example what one can  
find when trying to look at the COTE and FOTE bill tip during the fall. I went  
before and after the month of November. This was not planned yet as I am 
still  in process to put together plumages from other times of the year.
 
_http://www.pbase.com/mbb/image/147740473/original_ 
(http://www.pbase.com/mbb/image/147740473/original) 
(this  is high resolution image so be sure you are looking at original at 
pbase)
 
One can see for him/herself; please remember that those are only a few  
quickly accessed examples - more thoroughly analysis will, hopefully, follow in 
 the future. Note that FOTE can and usually has small yellowish bill tip 
and COTE  might have only hint or none (COTE A,  D and F - examples chosen 
from  August to December). BTW if one is only looking for lack of yellowish tip 
now  this might lead to misidentification (recently taken COTE A and D). 
Extreme COTE  case (G) - it seems to be seen rarely and as bird was changing 
bill color it  could ended up in much smaller yellowish tip (see also F from 
the same day that  only show hint of color). As you can see in FOTE A-B 
Forsterâs is changing bill  color in December and as well can has darkened 
cap. 
 
I am grateful for all there emails as they allowed me not only to look  
deeper into traits that some people might try to use but also there is always  
possibility that I might learn something new. Knowledge about terns 
especially  how and when they molt is to say at least quite shallow and there 
is a 
lot left  to learn. I was writing this in the hurry so I might add word or 
two or even  more photos in the future.
 
Have fun with terns, I for sure do.
 
Mark B Bartosik
Houston, Texas
_http://www.pbase.com/mbb/from_the_field_ 
(http://www.pbase.com/mbb/from_the_field)
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[texbirds] COTE vs FOTE bill tip color an overlapping trait

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