Fall Bird Aggregations
(This 1226th Buffalo Sunday News column was first published on September 21, 2014.)
A reader wrote recently to ask, "Why is there a big drop in bird activity in the village of Sloan?" That's a question that might well be asked about any local community at this time of year. There are a number of answers to this question and I offer a few here.
First, some species like bobolink are molting into their basic plumage and for that reason have retreated to hiding places in regional marshes.
I offer an aside about plumage names for adult birds. Some species molt just once each year and their single plumage is called basic plumage. Examples of such birds are chickadees, swallows and thrushes. Other species molt twice a year and their often drab winter plumage is also called basic. When we see these birds in their spring colors, they are in what is called alternate plumage. This may seem backwards to some readers but these species are in their winter basic plumage much longer each year than they are in their bright springtime alternate plumage. Examples of species that fit this second category are tanagers and warblers. Among feeder birds the goldfinch is a perfect example. I won't even try to describe the further plumage complications of gulls.
Back to birds disappearing. Second, some have already left on their southward migration. Those yellow warblers that were so prominent through spring and summer have headed south.
But third, many species are organizing into family groups and larger flocks. Thus you find all or none situations. One woodlot may have no birds whatsoever and the next one may be full of birds. Also, because birds like cedar waxwings wander in search of the best berry crops, you may be inundated with them today and find none in your neighborhood tomorrow when your grapes have all been eaten.
Larger flocks indeed. At the suggestion of Alec Humann a few weeks ago a group of us went one evening to Buckhorn Park on Grand Island to watch a huge flock of purple martins gather before dropping into a small cattail marsh in the middle of the Niagara River. This was one of the largest groups of native birds I have ever seen and I found it impossible to estimate their number. I am told, however, that one estimate made by photographing them, counting a small section and extrapolating from that to the entire area of the flock produced well over 10,000 birds.
One thing I noticed about the martins. There seemed to be no pattern to their flight. They were moving every which way and it is a wonder they didn't bump into each other. Only when they finally dropped into the marsh did they seem to act in concert.
What also amazed me about the numbers of these birds is the fact that I don't think of martins as very common. Increasing numbers of people erect those multiple houses for these birds but I would never have estimated our local birds to add up to this mob. It looked to me as though we had all the martins in North America overhead.
But I have seen still larger flocks. Among non-native birds starlings are surely the champions in flock formation. Not only are their numbers amazing but their flock behavior is absolutely remarkable. Flying perhaps at most a foot or two apart, they act in concert. The entire flock appears like a single entity, turning and twisting through the sky. 
I once watched a peregrine falcon fly past such a flock, which maintained its cohesiveness but bent slightly away from the raptor. It seemed clear to me that the tight flock organization provided a kind of protection for the birds.
For a film of a spectacular murmuration of starlings in Gretna, Scotland, see this website.
A lesser grouping of birds before they leave for the south are the lines of swallows you find on any drive along the shores of Lakes Ontario and Erie. It is not uncommon to find five swallow species represented among a group of 50-100 birds.
One last reason for the disappearance of birds at this time of year. Many species are fattening up for migration and for that reason they abandon feeders for the greater protein diet provided by insect prey.