MOBBING BIRDS

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One of the most amazing behaviors exhibited by birds takes place when a predator is present (or suspected to be present).  Though it takes a variety of forms in response to different types of predators, mobbing behavior is so widespread among so many types of birds that it seems to be more or less universal.   From a practical standpoint, mobbing behaviors make finding and seeing small, shy passerine birds an order of magnitude easier than it would be unaided.   The response of passerines (and some non-passerines, like woodpeckers) to a recorded screech owl tape is sometimes nothing short of miraculous.  Within a minute or two of turning the tape on, flocks of dozens of birds may materialize seemingly out of nowhere, and for a few minutes, engage in a frenetic, often vocal, and agitated search for the source of the call.  The photographs on this page were all obtained using this artifice, as were nearly all of the passerine bird photographs elsewhere on these pages.   Do I feel guilty tricking these poor, helpless little birds?  A little... but don't lose sleep over their fragile little psyches - they very quickly realize that there is no predator present and go back to what they were doing previously.  A typical mobbing response to a screech owl tape is over within 5 minutes, and the birds that were just moments before hyperkinetic cannot be again fooled for at least several hours, and perhaps longer.

            

Black-and-White warblers are often found in small numbers in mixed species foraging flocks of winter birds, and are often vocal, calling their metallic sharp chip note at a rapid rate.  I can usually tell when one is around before I see them because of the distinctiveness of their calls.

            
Though yellowthroats have declined a bit in conspicuousness in the latter part of October and November, they are still widespread and common.  Those are females above and to the right, a male above right.        

Warblers aren't the only interesting migrants/winter residents at Emeralda.  I saw one or two painted buntings for 4 or 5 weeks in a row, though the last was several weeks ago.  A few birds may winter on the flow-way, but they are relatively inconspicuous.  Those are both females above left; I haven't seen any of the spectacularly colored males on my surveys.  Too bad.    Indigo buntings (above right) are even more inconspicuous once they've molted into winter plumage.  Small flocks of a couple to a half dozen birds were present for over a month during the peak of migration, but most have probably departed for their tropical wintering grounds by now.

     The behavior of different species of passerines in a mobbing flock seems to be quite distinctive and species-specific.  Some species, like blue-gray gnatcatchers, are persistent and fearless mobbers.  Others, like this prairie warbler, are a bit more cautious.   Though they will occasionally approach closer than about 30-40' as this bird did, they don't usually stay that close for long.  I got one shot of this bird before she disappeared.  Some species, like orange-crowned warblers, are even more cautious.  I'm still waiting for my first shots of them.
          

Blue-headed (or solitary) vireos (above left) and ovenbirds (above right) are not uncommon participants in mobbing flocks, but are difficult for different reasons.  The vireos will sometimes approach quite closely, but quickly move away or leave the flock.  One or two photo opportunities per sighting are about the best you can hope for.  Ovenbirds will often remain in the vicinity of the owl call for some time, and occasionally will approach quite close.  They nearly always stay somewhat hidden or obscured by branches or foliage, though.  The shot above is the clearest I've been able to get so far.

Phoebes are somewhere in the middle.  Like most tyrannid flycatchers, they usually perch in very exposed, conspicuous sites, and they are no different when a part of a mobbing flock.  This would seem to make for an excellent photographic subject, but not unless you have a monster telephoto lens.  They rarely perch closer than 50-60' away.  The two birds below are quite different.  Both blue-gray gnatcatchers and ruby-crowned kinglets are among the smallest of the mobbing birds, but generally the most fearless.   Both species will often perch within 5-10' of the car or hover in mid-air right in front of my face.   Unfortunately, both species are incredibly active and rarely perch in one spot for long.  I still don't have any decent shots of ruby-crowned kinglets - they have to be the most hyperactive of the small passerines.
            
            
Then there is the reliable standby - the yellow-rumped, or "myrtle", warbler.  Present in small to large numbers in nearly every mobbing flock in the winter, they are about as cooperative as any species.  They often come in quite close, they sometimes perch right out in the open in great light, and they tend to be persistent.  They are usually among the last birds to leave a mobbing flock as the fervor subsides.  I probably take them for granted more than I should - even though they're not the most spectacular or exciting bird at Emeralda, they have their own unique charm.       

One of the peculiarities of mobbing behavior is the tremendous variability in the response shown by birds at different times of day, different times of year, etc.  It seems to be at a peak in the fall,  and perhaps declines somewhat during the winter.  During the last week or two, the intensity with which most of these species respond has declined a bit, or so it seems to me.    Come next spring, though, most birds will pretty much completely ignore the owl calls that they so intently sought out just a month or two earlier.   I sure wish I had a better idea of why that is so.

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