Dear reader: I'm unable to upload the picture Karen Kolling refers to below [or any picture, for some reason.] You can go to Palemale.com and find the grackle/hawk sequence in the June-December 2006 page, July 4 sub-section. Marie
Karen Anne Kolling writes:
Below's a picture from Lincoln's web site. It looks like the grackle actually hit the young redtail's head? I am wondering why the hawks put up with the apparently frequent harassment from smaller birds as opposed to sticking out a claw or beak and dispatching them...
John Blakeman replies:
Yes, the grackle almost surely landed for an instant on the hawk's back. The hawk just sat there and endured this harassment. I've seen this many times, both in wild hawks like the one pictured here, and also with my captive falconry birds perched out in my backyard. This scenario is familiar to all who have watched red-tails in the summer in the wild.
Why doesn't the hawk just quickly plunge a fistful of talons into the pesky little grackle? It's not as easy as it might appear. The grackle remains in the hawk's leg length for just an instant, and for the hawk to extend its leg would require that it shift its weight onto the other perching leg. In short, red-tails aren't built to easily thrust out a leg while sitting on a perch. The grackle "knows" this (No, it doesn't "know" this as we might -- it is only genetically programmed to shoot in and out quickly, avoiding capture.), that the hawk simply can't leap up and grab it with any ease while perched. The grackle is doing this because it's still in breeding mode. The blackbird probably has fledglings in the neighborhood, and by harassing the hawk as it is, the raptor's attention is diverted from any little grackles nearby. In August, these diversionary attacks generally stop, when vulnerable little bird youngsters are fully on the wing and safe from the larger, lumbering hawk. This is a seasonal event.
The photo is interesting for two other points. First, this hawk looks to be a female, from the thickness of the tarsus, the "ankle." To me, I'd bet this is a female.
But the more interesting observation is the emerging red tail feathers. Viewers should note that the red tail feathers are not as long as the brown, older banded ones. The bird was hatched in 2005. She is a second year red-tail, now in its first molt. The two central "deck" feathers have replaced the immature ones.
The shorter length of the adult, red tail feathers is normal. The same thing happens with the long primary feathers of the wings. This is why immature red-tails often look larger than their parents. Birds in their first year don't have completely developed, strong wing muscles, so their wing and tail feathers are a tad longer than they will be in adulthood. Immatures have lighter wing loading, spreading the body weight over a larger feather area. This helps them fly more easily with their weaker musculature. In the second year, with adult, fully-developed muscles, shorter wings and tails can allow greater maneuverability.
Experienced red-tail watchers can usually separate soaring immatures from adults merely by the respective tail lengths. Long-tailed red-tails are immatures. Adults are a bit more compact, while being also much more powerful.
The red tail feathers in the picture are fully grown, a bit shorter than the older brown feathers being replaced during the molt this summer.
And this bird is one of the few that was able to survive its first winter. Red-tails have a general 60-80% first year mortality. Only one or two red-tails out of five that leave the nest are able to survive their first year. This bird, where ever she was raised, is already a winner. The harassment by the grackle is inconsequential. Her greater problem next spring will in finding an open territory and a mate.
Bioblitz I, June 27, 2003 Photo by Danielle Gustafson
The second Central Park BioBlitz took place from Friday, June 23 to Saturday, June 24. At the event various experts cooperated with volunteers in a census of all living creatures to be found in Central Park. The event was sponsored by the Explorers Club and The E.O Wilson Biodiversity Foundation and hosted by the NYC Dept. of Parks, the Central Park Conservancy and the Urban Park Rangers.
During the BioBlitz volunteers joined teams searching for various taxonomical groups -- i.e. insects, reptiles and amphibians, birds, mammals. As in the last Bioblitz I joined the Bat team. Our stint: to 11. Our destination: the North Woods.
Our expert was Carl Herzog, a wildlife technician with the New York State Dep't of Environmental Conservation [DEC] and a highly knowledgeable bat person. Also on our team were three local bat experts familiar with the bat population of Central Park, one of them Danielle Gustafson. Then there were four or five others such as me, attracted by the romance of bats and the allure of the park in the dark. We were not disappointed.
We were literally detectives, because we carried bat detectors. Carl also carried a portable computer to which one of the detectors was attached.
What exactly is a bat detector? As you may know all bats use echolocation to help them hunt in the dark. They zero in on their insect prey by emitting high-pitched sounds and then listening to the sounds' ehoes when they collide with objects in the air. The objects are inevitably insects. The echoes provide the bats with information about the direction, size, shape and velocity of their insect prey.
Echolocation is a relatively new concept. Towards the end of the 19th century a Swiss zooologist came up with the idea that bats hunted with their ears instead of their eyes. But his theory was rejected completely. Not until 1944, inspired by military research at the beginning of World War II [Sonar, Radar etc] did Donald Griffin, who was then a Harvard undergraduate, come up with an elegant experiment firmly demonstrating that bats do, indeed, navigate and hunt in the dark via ultra-sonic emissions and their echoes. His book about his discovery, Echoes of Bats and Men, is a classic of science reporting.
But why the detectors? Couldn't we simply find bats by listening for their calls as we listen for bird songs? As you may know the echolocation calls emitted by bats are too high for us to hear. Bats produce sounds in frequncies between 20 and 200 kiloherz [kHz]. while the human ear generally cannot hear sounds above 20 kHz.[Well, very young people can sometimes hear frequencies a bit higher, as recent newspaper articles have reported, an ability teenagers exploit by programming cell phone rings above 22 kHz that their teachers cannot hear.]
Bat detectors are hand held instruments that can pick up those high-frequency sounds and translate them into lower frequency sounds we can easily hear. When a bat comes into range. the bat detector begins to click loudly.
Carl's computer was programmed to record and analyze the particular bat emissions being picked up by the detector at any given moment, thereby giving a clue to that particular bat's species.
The bat team set forth at on Friday from Bioblitz headquarters at the NorthMeadowsRecreationalCenter. With all detectors turned on we made our way to the nearest body of water, the Pool , as it is called, a little pond between 100th and 103rd St.[ There is another little pond in Central Park, at 59th St., that is called, oddly enough, The Pond.] On our way we looked out for Black Locusts and Shagbark Hickories, both trees with rough, flaking bark. These, we learned, might offers nesting opportunities for local bats. But the bat detectors revealed no bat action in the woods. Several trees had large hollows we thought might serve as bat homes. No, Carl, said, bats avoid large openings. Very small crevices offer far better protection from predators. What predators might bats encounter? Raccoons, among others. Central Park seems to be wall-to-wall raccoon this year.
We were nearing the Pool when we heard our first clicks. It was about . We stopped near a street lamp and actually caught a few fleeting glimpses of bats, dark, erratically flying shapes swooping between trees and the water. According to the frequency range indicated by the bat detectors, and also by the bat experts' glimpses, these were probably Little Brown Bats. The final report, based on further analysis of the computer recordings, will be available on the Explorers Club website in a few weeks; until then my report here is tentative.
To be sure many bat species emit sounds within a range of frequencies that overlap with other species. The frequency range of the Little Brown Bat is 38 - 62 kHz. The Big Brown Bat's range is 25-51. So if you detect a frequency of, say, 45 kHz, it could be either. Then the visual information is crucial: one of these is a lot bigger than the other. You can guess which one.
We took a path from the Pool down a slope and under the Glen Span Arch. Our next waterbody was at hand -- the Loch, a little meandering stream that flows picturesquely through a deeply wooded area, under another bridge [Huddlestone Arch] and into the Harlem Meer. Sure enough, as we approached the Loch the detectors began to click again, like Geiger counters at a radium lode.
As we approached our last waterbody, the Harlem Meer, we were not surprised to hear another fusillade of clicks from the detectors. One bat here was a surprise. Based on a sighting as well as the computer report, Carl believed he had found a Northern Long-eared Bat, a species never before identified in Central Park. This sort of discovery is what a Bioblitz is all about. Our team felt triumphant, as if we had found a new species of bird in the South American rain forest, or, at least, an Ivory-billed Woodpecker in some lonesome bayou.
On our way back we ran into the Reptile and Amphibian team. They did not seem quite as elated. They had only one species on their list: the bullfrog.