Bioaccumulation occurs when a substance becomes concentrated inside the body of a living thing. It happened with DDT, which concentrated in bald eagles, peregrine falcons, ospreys and others, and made their eggshells to thin so they broke easily during incubation. Those species recovered when DDT was banned in the United States on Dec. 31, 1972, though it is still used in many tropical countries.
There now is another chemical that is bioaccumulating in avian predators. According to a recent article in Cornell Laboratory of Ornithology’s Living Bird magazine, brodifacoum effectively poisons rats and mice, but there is a time delay before it dies from internal bleeding. The poisoned rat becomes thirsty, so it leaves the area in search of water. As the rat nears death, its reactions slow down so it becomes more susceptible to predation by hawks, owls or other carnivores. The predator assimilates the brodifacoum into its body, which accumulates into lethal dose if it eats multiple dying rats.
Because of the frequent use of rat poison, brodifacoum is widespread in red-tailed hawks, great horned owls, eastern screech owls and barred owls. The Tufts University Wildlife Clinic documented that 139 of 161 predators (86 per cent) brought to the clinic between 2006 and 2010 contained brodifacoum, though usually not enough for it to kill the predator. And the Cornell University College of Veterinary Medicine has confirmed that these poisons have caused 39 deaths since 2011. The number of deaths is undoubtedly much higher since most of carcasses are not analyzed for these chemicals.
The Environmental Protection Agency recently enacted a partial ban of brodifacoum. It is only a partial ban because of lawsuits by the manufacturers. Agricultural uses are still permitted and stores are allowed to sell their existing inventory of this dangerous chemical.
Hopefully, the partial ban will reduce hawk mortality due to brodifacoum. And it is nice that the ban takes effect before the chemical contamination causes the extreme population declines of the DDT era.
Bird Sightings
Hummingbirds are still around, although most of our summer-residents have left for the season. Sarah Mayhew, Barbara Beicheck, Charlie Kernick and Linda Mariano have had them in their yards recently. Has anyone seen them other than in their yards? I have checked a few sites with abundant jewelweed (touch-me-nots) but have not seen any hummers visiting these bright orange flowers.
Ken Magnuson found a kestrel hunting the Farm Institute’s fields on Sept. 24, while Soo Whiting and Flip Harrington observed one of these small falcons at the Gay head Cliffs on Sept. 22. Mr. Magnuson also reports many green-winged teal, some blue-winged teal and three pintails.
At last, golden plovers have shown up. Warren Woessner found one on Norton Point on Sept. 22. It seems like they are few and far between this year. I have not found any in their usual pastoral haunts this month.
Sarah Mayhew has been out in the field a lot this week. On Sept. 22, she found an American redstart at Gay Head Morraine, and on the Sept. 24 at Aquinnah, she (along with Allan Keith and Bob Shriber) found common yellowthroat, house wren, red-eyed vireo, cedar waxwings and chipping sparrows. On Sept. 25, she spotted the northern waterthrush that is hanging out behind the Chilmark Store, and a blue-headed vireo at Wascosim’s Rock Reservation. She happily reports that a pair of Carolina wrens is thriving at her house. Dionis Montrowl and Katherine Welch also have wrens at their houses. Their population is definitely on the rebound from last winter’s cold and snow.
Lanny McDowell heard and saw a flock of 16 fish crows as they noisily flew over his house on the morning of Sept. 24. This is the first report of our roosting crows that commute daily to the Cape to feed, as they were flying to the east-northeast toward West Chop. In other years these commuter crows, here for the winter, were not observed until mid to late October.
Ms. Whiting observed a black-throated green warbler and a red-eyed vireo bathing in the bird bath in her yard. She also reports flushing an American woodcock from Quansoo Road on Sept. 20.
On Sept. 26, my guided birding tour went to Little Beach despite the high tide and easterly winds. We were able to find an American oystercatcher, 150 sanderling, 100 black-bellied plovers and at least 50 greater yellowlegs hiding in the salt marsh along with at least one lesser yellowlegs and five willets. An osprey flew over and a red-tailed hawk was chased away by five crows.
Ken Magnuson was in Aquinnah on Sept. 26 and 27 and accumulated the following highlights: orange-crowned warbler, northern waterthrush, indigo bunting, and clay-colored sparrow. Bob Shriber was also there that day and he adds an adult white-crowned sparrow to the list.
Sarah Mayhew found a northern parula at Fulling Mill Brook on Sept. 27.
On Sunday morning I visited the Head of the Lagoon and spotted a northern waterthrush and a black-throated blue warbler. Perhaps the most unusual sight was a great blue heron and a green heron perched about five feet apart on the same branch. The green heron looked really small in comparison. A solitary black-crowned night-heron flew out from behind the stone pump station building.
Lanny McDowell and I were in Aquinnah on Sept. 28, and our highlights included a dickcissel that we heard but did not see, red-eyed vireos and one yellow-rumped warbler. Six white-winged scoters and six double-crested cormorants were just off-shore from the overlook, and there were lots of catbirds, blue jays, eastern towhees and northern mockingbirds.
There are lots of birds around, so please get out looking for them, and be sure to report your bird sightings to birds@mvgazette.com.
Robert Culbert leads Saturday morning guided birding tours and is an ecological consultant living in Vineyard Haven.
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