[TN-Bird] Migrants in Costa Rica: Que pasa?

From: "Dev Joslin" <devjoslin@xxxxxxxxxxx>
To: tn-bird@xxxxxxxxxxxxx
Date: Sat, 18 Dec 2004 10:20:10 -0600
Just a few observations on the activities of North America migrants in the 
Monteverde, Costa Rica area:

CALL NOTES in FORAGING FLOCKS:  Most of our North American migrants feed 
here in foraging flocks.  The local year-round residents seem to lead the 
group and are by far the most vocal?chipping almost all day long and setting 
off warning notes when a human (or other intruder) appears.  Meanwhile, 
almost all the migrants in these flocks?Black-throated Green warblers, 
Black-and-white warblers, Golden-winged warblers, Blue-winged warblers, 
Tennessee warblers, Yellow-throated Vireos?are either totally silent (or are 
so quiet I cannot hear them).  It?s the local Common Bush-tanagers, 
Golden-crowned Warblers, and Slate-throated Redstarts that make all the 
noise.
        This all seems logical enough to me.  Why call attention to yourself 
when someone else who knows the territory is doing all the work?
        What makes no sense to me is why the NA migrants that do most of 
their foraging alone are the only ones that chip all day long.  The best 
examples are Wilson?s Warblers and Chestnut-sided Warblers (on the Caribbean 
slope).  Why would a bird foraging alone (with no one to call to because he 
is feeding alone) call attention to itself by chipping all day?  One 
possible answer is that they are being territorial?but I have observed no 
other territorial behavior.  Both species are totally tolerant of other 
birds coming close and seem totally oblivious of them.  Similarly they are 
not at all shy about human approaches.  Any possible explanations out there?

FORAGING IN THE RAIN:  It has been raining here now non-stop for 6 days (a 
typical December ?temporal del Atlantico?).  That?s 144 consecutive hours 
without a break, more or less.  So how do insectivorous birds manage this 
weather?  The best I can tell is that they mostly ignore it.  Most of the 
rain is in the form of a very steady drizzle and/or steady light rain.  
Foraging flocks seem to keep on feeding through it all, to my amazement (and 
soaked skin); somehow they still seem to find caterpillars and other insects 
despite the weather.  I have even watched Blue-and-white swallows and 
Tropical Kingbirds catching insects on the wing during the rain.  Don?t ask 
me what insects are out there flying around in this weather!

MOVING ON SOUTH:  Where are your migrants now?  Well, as far as the 
Monteverde area goes, some have moved on (either further south towards South 
America or to lower elevations where it is drier and warmer).  The Eastern 
and Western Pewees, so common here in October, are long gone further south.  
The large flocks of Baltimore Orioles have passed by, leaving just a few 
here and there that decided to stay the winter.  Others that were common 
here in early November, but are now no longer here, include Red-eyed Vireos, 
Scarlet Tanagers, Rose-breasted Grosbeaks, Wood Thrushes, Swainson?s 
Thrushes, other thrushes, and Empidonax spp.

STILL AROUND:  Most common NA migrants still here for the winter are the 
warblers and vireos mentioned above plus a few Broad-winged Hawks and 
Baltimore Orioles and lots of Summer Tanagers.  Most common of all are 
Wilson?s, Black-and-White, Tennessee, and Black-throated Green Warblers.

SAPSUCKER!  In late November I was surprised to see a Yellow-bellied 
Sapsucker.  Common enough in winter in Tennessee, I had no idea they came 
this far south.  Apparently this is the southern extent of their winter 
range and they are quite rare here.

All for now.  Your Costa Rican reporter,
Dev Joslin
Monteverde, Costa Rica


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[TN-Bird] Migrants in Costa Rica: Que pasa?

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