Migrant Fallout, Tuesday, 5/3/2011

Gray Catbird photo by Leo Kulinski, Jr.

from whalesandwolves.com

Red-winged Blackbird immature male

photo by Bob Stanowski

In ornithological terms a fallout is any mass downing of birds from their flight. It is usually caused by storms or other bad weather, but can also be caused by exhaustion or hunger. In the cases of the latter 2 causes they most often happen after birds have crossed a large expanse of water (like the Gulf of Mexico) or have made some other very long flight. Fallouts caused by storms or other foul weather can occur anywhere. Sometimes the weather doesn't even have to be all that bad to bring birds down. That was the case this past Monday night and Tuesday morning when conditions were cloudy and a little foggy with a couple of showers and some drizzle. It was unpleasant, but by no means severe. However, it may have been bad enough to bring a lot of birds down to the N. Shore Marsh and several of White Memorial's trails that run along or near this large wetland. It was also obvious that these birds were hungry, as I saw a lot of feeding activity. Lucky for them, fishflies and other insects were in abundance. I headed down there around 2 p.m. with the intention of conducting our first Breeding Bird Census of 2011. Even though the spring migration is still in full swing, some birds, like Red-winged Blackbirds and Swamp Sparrows, are establishing territories for the upcoming breeding season. Now that N. Shore Marsh is more of a shrubby hardwood swamp than a marsh it regularly hosts almost 50 species of birds as nesters. Back in the 1960's, '70's, and '80's when this wetland was mostly mixed herbaceous and shrub marsh it only hosted about 20 species as nesters. In this case, succession has been beneficial to birds. Many species have been added to this area, while very few have been lost. On Tuesday I found 66 species, many of which would never breed in a wetland. A lot of these were in trees and shrubs along the Lake, Windmill Hill, Ongley Pond, and Mill Field Trails as they run along the northern border of N. Shore Marsh. For species that do breed here it was difficult to tell which individual birds are likely to remain as summer residents and which were migrants that will move on northwards. That's why I try to conduct 10 censuses of each of our 5 Breeding Bird Census plots from early May through late July. This helps to weed-out the breeders from the migrants. Though I was tempted to publish a complete list of the birds that I found Tuesday, I decided that it would be unnecessary since readers can go to ebird.org to view it. Instead, shown below are the species that I found in higher-than-average numbers for early May and their average expected numbers in parentheses:

Northern Flicker - 12 (4); Great Crested Flycatcher - 10 (4); Eastern Kingbird - 14 (4); Blue-gray Gnatcatcher - 19 (6); Gray Catbird - 33 (16); Yellow Warbler - 69 (22); Common Yellowthroat - 23 (12); Song Sparrow 24 (8); Swamp Sparrow - 31 (24); Red-winged Blackbird - 88 (40); Common Grackle - 92 (30); Baltimore Oriole - 13 (3); American Goldfinch - 44 (10)

Some of the figures above also include birds seen at the Museum Feeders and in Ongley and Activity Fields. These birds regularly commute back and forth between these areas and N. Shore Marsh. Other birds seen in higher-than-average numbers around all of the above-mentioned areas combined included Black-capped Chickadees, Tufted Titmice, American Robins, Pine Warblers, and Black-and-White Warblers. These last 2 species were twice as abundant as usual. Some of the other species, like titmice, aren't generally considered to be migrants, but their recent upsurge in numbers might indicate otherwise. Some of the other species, like Red-winged Blackbirds and Common Grackles, stage much of their migration activity in March and April, but are obviously continuing to move through so far this month. With persistent lousy weather it is no surprise that the migration is prolonged this year, and that fallouts are occurring.

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