Date: 6/20/25 12:53 am From: Davy Bosman <bosman.davy...> Subject: Re: [BIRDWG01] Colorado Booby ID
Hi,
Maybe somebody should go back to that tree. See if there is some dry
'droppings' to be collected with a wet (not saliva) eartip? Or maybe the
bird shed a plume? If that is not already done of course. There must be a
genotypical difference, because why otherwise is this a seperate species?
Grtz. D.
Op do 19 jun 2025, 23:17 schreef David Sibley <sibleyguides...>:
> Following up on this after more photo study. I still think this bird is a
> better match for Atlantic Brown Booby, but can't rule out Cocos with
> certainty.
>
> For comparison, this subadult Brown from Maryland is an almost exact match
> - https://macaulaylibrary.org/asset/624857879 > This Cocos from Costa Rica is also very close -
> https://macaulaylibrary.org/asset/629034516 >
> Bill color, bill shape, and eye color seem to be no help in ID.
>
> One thing that does seem fairly consistent in photos I've looked at is
> that Cocos has a wider ring of bare skin behind the eye, and by that
> feature the Colorado bird matches Brown.
>
> And the bare skin on the chin of Cocos seems to average a little drabber
> and greener, Brown Booby more yellow, again the CO bird matches Brown.
>
> Those are pretty much the only differences I can see for a subadult female
> like this, and for now I would not feel confident identifying either
> species out of range based on those things. But maybe one could argue that
> Colorado is within the "expected" range for Brown Booby?
>
> Colorado's prior record looks like an adult female Atlantic Brown Booby.
> Cocos adult female typically has a greener face and darker brownish bill
> (but there is overlap).
>
> Best,
> David
>
> <sibleyguides...>
> www.sibleyguides.com
>
>
>
> > On Jun 18, 2025, at 11:57 AM, Rachel Hopper <hopkohome8...>
> wrote:
> >
> > Colorado just had its second record of a booby, found on June 16th &
> seen early again on the 17th after which it disappeared.
> >
> > It was found in a tree out on the prairie in far SE CO. No water body
> even close.
> >
> > There are several photos of the bird, which did take flight a few times,
> always coming back to land in an Elm tree. At one point it was on the
> ground.
> >
> > We are trying to determine if this is a Brown Booby or Cocos Booby.
> Possibly not a full adult. Any help would be appreciated.
> >
> > You can view the photos of the bird here on these 3 checklists:
> >
> > https://ebird.org/checklist/S251486607 > >
> > https://ebird.org/checklist/S251577330 > >
> > https://ebird.org/checklist/S251215877 > >
> > -----------------------
> > Rachel Kolokoff Hopper
> > Ft. Collins, CO
> >
> >
> > Archives: https://listserv.ksu.edu/birdwg01.html >
>
> Archives: https://listserv.ksu.edu/birdwg01.html >
