Wednesday, March 26, 2008

NYC Audubon Hawk Report and Blakeman's comments

Riverside Park female Red-tailed Hawk sitting on nest -- March 2008
Photo by Bruce Yolton ©

Hawk Report from the NYC Audubon Raptor Census

Those who breed regularly and in greater numbers are listed first and in greater detail.

A large number of birds were found through the census, including eight species confirmed to be breeding within city limits. In addition to the five diurnal species, three species of owl are found in the city year round and are covered separately from the diurnal species. Seven of those species are widespread, the eighth, Cooper’s Hawks, were confirmed as breeding only once. Species not confirmed as breeding within city limits, including migratory species, those found only in winter, and those species found in areas near the city and who may occasionally cross its borders, are not addressed in the same detail.

Cooper’s Hawks, Accipter cooperii
Cooper’s Hawks were the rarest of the species confirmed as breeding in the city with only one confirmed pair and two probable breeding pairs. They were reported in Brooklyn, the Bronx, Queens and Staten Island. The Bronx had no confirmed or probable breeders, Queens had two probable pairs and Staten Island had 1 confirmed pair.

Red-Tailed Hawks, Buteo jamaicensis
The census found 20 Red-tailed Hawk nests in addition to 12 pairs whose nest locations are unknown. Adult Red-tails have been recently sighted at four additional locations however further information was not available. The occurrences of reports of Confirmed or Probable breeding are as follows: three CO in Brooklyn, two CO and one PR in the Bronx, five CO and one PR in Manhattan, four CO and five PR in Queens, and seven CO and four PR in Staten Island.

Among the known nesting locations the number of eggs laid and the number of young fledged is unknown. Some nests were monitored closely by various birders, others were not, either due to their remote locations, or the fact that a nest might only be known to a select few individuals. The offspring data that was collected was incomplete due to the same aforementioned factors. Therefore, the numbers obtained are incomplete.

Citywide, 28 eyasses were recorded, split up among 12 nests. Two nests were known to have young but actual numbers were unknown. In these cases, the number of young in the nest was recorded as being one. Brooklyn had four young, Bronx had three, Manhattan had eight, Queens had seven and Staten Island had six young. Two of the pairs whose nests were observed failed to rear young. One of these produced an egg which did not hatch. For the other, no data on eggs is available. All hatched young observed fledged successfully.

This census used a new method to gather information. In the NY Breeding Bird Census, volunteers walk or drive along predetermined routes. At set distances along the route they stop and record all the birds that they hear or see for a specified length of time. The specific quarry being censused, combined with the size of the area involved, made this a difficult approach to take; therefore, it was decided that information should be obtained by interviewing knowledgeable individuals.

Due to the nature of the methods used to gather information, getting precise numbers on any species was difficult. For some species such as Red-tailed Hawks and American Kestrels, the census data are likely lower than the actual numbers due to a lack of adequate coverage of certain areas (as with Red-tailed Hawks) and/or difficulty in finding the birds (as in kestrels). For other species, the numbers here might be higher than the actual ones due to mistaken identification, overlapping reports that are not recognized as such and inability to accurately assess the exact numbers found in an area. In all cases, steps were taken to be cautious and err on the low end. Nonetheless, the final numbers can be considered a fairly representative picture of the city's raptor population.

Cooper's Hawks were the rarest of the confirmed breeding species having only one breeding confirmation and two probable breeding pairs reported. It is notable however that the species is more common than that would suggest- in addition to the three pairs mentioned, Cooper's Hawks have been seen in five additional areas around the city, occurring in every borough except Manhattan. In all instances, the birds have been associated with parks or cemeteries. Red-tails were the easiest birds on which to find information. They are large and conspicuous. Even better, they have a large number of devoted birders or hawk watchers who keep close track of them.

The first pair of Red-tails to live in the city appears to have been Pale Male and Lola; they were first discovered living on 5th Avenue in 1991. Since then, the number of Red-tailed Hawks has grown. The numbers found in this census are likely lower than actual numbers. While in the wild Red-tailed Hawks nest on trees or rocky ledges, New York City pairs seem to feel equally comfortable nesting on the sides or roofs of buildings. Of the nests whose locations are known, ten nests are built on trees and eleven are nesting on man-made structures. Seven of the latter were built on buildings, two were on bridges, one on a sculpture and one on a crane.

A stronger need than nesting on trees or buildings seems to be nesting in or near parks. Of those 21 nests mentioned, only one is not located right next to or inside of a park. Many of the Red-tailed Hawks in the city appear to maintain small territories compared with their rural counterparts. Moreover, at least one observer noted their increased tolerance, both of other Red-tails and members of other species, intruding on their territories. This could indicate that food availability is fairly high.

The reproductive success of the observed nests is high. Two nests were known not to produce young; both of those had reportedly failed to do so last year as well. This may be a result of age or some other biological factor. In order to determine that, more research would need to be done. There does not appear to be a difference between the reproductive rates of those nesting on trees and those nesting on buildings or other structures.

There are still dangers associated with living in the city. One of the pairs that built their nest on a bridge inadvertently built it on a section of the bridge that was slated for demolition. In addition to the nest itself being in danger, nearby trees which could be used by the newly fledged chicks once they left the nest were removed. The wall was left up until the chicks left but what happened to them afterwards is unknown.

Manhattan Hawk Report
by Bruce Yolton

Red-tailed Hawks, along with Peregrine Falcons and Kestrels are doing especially well in Manhattan and the rest of the city. Red-tails have established at least seven nesting sites in Manhattan this year, up from five last year. So, the state of Red-tails has changed from a status of being rare and unusual, to one where they are now common place. The new question is how soon will all the available territories be filled in by the species.

It's an exciting time to be studying their urban expansion.Of the eight known nests in Manhattan, here's their status this week...

5th Avenue, Lola sitting on the eggs.

888 Seventh Avenue, Lots of mating and twigging. Not sure if brooding has started.

St. John the Divine, Not sitting yet.

Highbridge Park, New nest location. Female sitting on eggs.

Inwood Hill Park, New nest location. Female sitting on eggs.

South Riverside Park, Female sitting on eggs.

Houston Street, Female sitting on eggs. The male picked up earlier in the month downtown, turns out NOT to be from this nest.

Shepard Hall, City College, New nest. Not sure of status.

And in the Bronx, Chris Lyons reports Rose is sitting on the Fordham University nest.

For more information about Urban Hawks and Bruce Yolton, please visit Bruce's website

John Blakeman sends in a comment about the NYC Audubon report:

For me, the question now becomes, "When will NYC become saturated with Red-tails?" It would be interesting to plot the number of nests and pairs in each borough and the entire city and region each year.. Through the recent years, and into the future, what's the shape of the population trendline?

Right now, it's obviously shooting up at a rather steep angle, with more new nests each spring. But sometime in the future the line will start to flatten across the top, with all the available territories becoming occupied. I'm sure saturation hasn't yet been achieved, but if the annual nest numbers are plotted, the leaning inflection point, when the slope first begins to flatten, will show that Red-tail "housing" has begun to get tight.

A note about the apparent paucity of Cooper's Hawk nests in NYC. :

Everywhere else these bird-eating hawks are exploding in numbers. They've invaded and nested in virtually every city, town, or village in Ohio and much of the rest of North America. But why do so few nest in New York City? Here's the reason,

I believe. Cooper's Hawks almost always prefer to have a small, flowing stream within a quarter-mile of their nests. Sometimes, a pond or lake will suffice, but a nest is almost never built in the absence of these close-by water features. Coop's like to take a bath each day, and they like to do this in flowing water.

I doubt that there are many free-flowing small streams in NYC. Manhattan certainly doesn't have any that would be acceptable. So the Cooper's Hawks seen in Central Park have flown over from New Jersey or down the Hudson Valley. But they will have great difficulty finding an NYC neighborhood with the small flowing stream they so much prefer for nesting. Until a population emerges that no longer prefers to take a daily bath, there will be few Cooper's Hawk nests in The City.