Monday, March 17, 2008

Blakeman On Downed Eyasses and Horvath on the Timing of the Placement of Artificial Branching Devices

Cathedral Nest 2006: While Youngest is still in the bushes cooling his talons and considering how to get into a tree...

Eldest has made it to safety on the scaffolding and is considering taking the stairs even higher.
John Blakeman's comments on downed eyasses and the number of young Red-tails in the city--

The conundrum of eyasses on the ground is a very sticky one, a conundrum indeed.

It's something that could turn out to be something of an annual problem in NYC. What happens when another eyass or two drop to the street from the 7th Ave nest? An eyass in the schoolyard? What about a Riverside eyass dodging vehicles on the road beneath?

In areas where a nest sits over a typical city landscape (hardscape), this could be a problem. At 927, the eyasses are naturally going to try to float over to the trees in the park. And they are starting out at 120 feet up, allowing them a bit of awkward maneuvering before crashing into the foliage of a tree. But at nest sites that have only typical streetscapes below, eyasses that fledge before being fully able to ascend on-wing are going to encounter problems, doubtless.

And I haven't any ideas on how these can be obviated. It may just be a hazard of living in The City, something Red-tails haven't much of a history doing.

An unrelated point. Recent photos by show the eyes of the schoolhouse hawks. As with the new pair at Riverside Park, the new pair at PS 188 don't have uniformly dense, dark brown irises, a clear indication that these are young adults, almost surely in their first nesting attempts. The photo of the nest on the air conditioner screen looks still pretty shallow. It looks like a loose, first-nest attempt. There is still time for some more stick additions, but if they don't happen this could be a problematic nest. The photo seems to show light coming from above, down through the sticks. It's still a bit thin.

But the very interesting thing for me is the preponderance of young adults in all of the new NYC nests. This substantiates my contention that these birds are colonizing Manhattan because favorable rural and suburban nesting areas are no longer vacant. The Red-tails in New York City and other large urban areas indicate that populations in historic wild and rural areas are now saturated with older, more defensive adults. All the good nesting areas outside of the city are occupied. Red-tails are seldom being trapped or killed out there anymore, so rising young adults no longer find annual, human-caused territorial "holes" that they can fill. As with Pale Male in the 1990s, the new birds have come into the city because it's the only habitat with ample prey and nesting sites yet available.

How soon, then, will Manhattan and the other boroughs become saturated themselves? How many Red-tail nests can Manhattan support? From it's prey base, with literally tons of rats and pigeons, there's enough food for 20 or 30 nesting pairs, or more. But Red-tails are not noted for being even quasi-social in allowing adjacent, close-by nests. Red-tail nest saturation of Manhattan and the rest of Greater NYC is likely to be controlled by the species' social tolerances, not the biology of the prey or nesting territories.

It will be fun to see how this develops in the coming years. Will the species retain its social intolerance of too-close adjacent nests? Or, will the abundance of prey tend to negate this territorial defensiveness? In California, where ground squirrels are ample, nest densities are greater than in the Midwest and East, where prey are harder to find. So who knows how many urban Red-tails might become residents of New York City? With several new nests just this year, how many might show up next year?

--John Blakeman
I'd asked the premier wildlife rehabilitator in the city, Bobby Horvath, his thoughts on placing artificial branching options, and as I suspected it is too late this year for the immediate areas around the nest, but---

Hi Donna,
The weather has been very mild here and the season will be in full swing earlier than normal I believe. About any possibility for erecting branching devices for the fledglings unfortunately for this year I think it might be too late to do anything. Any of the known breeding pairs that have nesting and or breeding activity could cause nest desertion if disturbed now.

The most common time for abandoning is just prior to or right after laying . In addition if they are uprooted it can cause them to look elsewhere for future nest sites. A few weeks after babies are born and flourishing the parents are much more likely to defend their territory and family but now could be a disaster for any type of new construction.

I've seen the pictures of the scaffolding [ At St. John's] but it was there before breeding so they are probably already adjusted to the structures presence. Many peregrine and osprey platforms do have additional perches attached for this purpose and they do provide additional exercise perches for the young to explore and practice on before the big leap. This one might have to wait till nest year to attempt.

We're keeping busy here. Already calls for baby grey squirrels.
Take care.
As folks have already worked up viable branching options on Osprey platforms that work, I asked Bobby about materials and design. Plus I've inquired about what might be needed to help eyasses back into street trees when no branching opportunities such as smaller trees or bicycle racks present themselves. We'll see what Bobby has to say.
Our friend from Illinois has also been investigating options. We may yet have something that could help the eyasses at St. John's and perhaps an even longer shot, those at 888 7th Ave. before the it's time for them to fledge.

Donegal Browne

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