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Is West Nile Causing NYC's Red-Tailed Hawk Boom (by Killing Crows)?

Robert DeCandido, PhD, a bird biologist who lively tours of owls and other avians in Central Park, has agreed to let me run his newsletter here. Birding Bob is always full of great information not only about New York City birds, but wildlife in general.
Photo courtesy of Flickr’s Bryce Bradford
Last week’s history of West Nile disease in NYC (1999-2009) prompted a few emails – folks filling in the consequences of this Asian disease post 1999. What has changed in the local environment in the last decade? Most noticeably, the American Crow population has not rebounded to pre-1999 levels, especially during the breeding season. And wintering populations of 50 or more crows in one park are unusual. Gone are the days when one could find a Great Horned Owl in many of NYCs (larger) parks by simply following the cacophony of crows surrounding the owls.

And during this same time frame, as the crows have precipitously declined as residents in NYC, the population of Red-tailed Hawks as breeders has increased exponentially. Is this simply correlation (two un-related events occurring simultaneously) or causation? Time may tell

A second noticeable change has been the decline in certain insect species – especially Tiger Swallowtail butterflies which were once common in our area in summer. There are other changes, such as a severe decline in Ring-necked Pheasants in our parks – these are verging on extinction locally…but tracing the decline of Asian pheasants to West Nile is more difficult – it might be mere correlation.

Finally, other insect species such as certain wasps that laid their eggs on the leaves of cherry trees have declined as well…but most people would not notice these even if they disappeared from our area completely.

In our Bronx neighborhood, one exotic bird species continues to increase, and is now nesting on at least a few Bronx streets. We even have them feeding in our pear trees in our yard each July-August: And while we are at it, another (native) bird has made a remarkable comeback as a breeding species since the late 1990s, particularly in Pelham Bay Park in the Bronx:
Our historical reports this week highlight a breeding pair of American Coots in Queens (2000); 70+ Cormorants in the Reservoir of Central Park (28 July 1999); and the first record of breeding Blue-grey Gnatcatchers in New York City at Pelham Bay Park (27 July 1999). Debs and I have seen families of Gnatcatchers there in July since 1999 – and Gnatcatchers have bred in at least one other NYC park (Prospect Park in Brooklyn, circa 2007). And to show that good things can still be found nearby, we include two news reports about dolphins in the Long Island Sound in late June 2009 (in Queens and the Bronx).
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Good! Here are the bird walks for this week ($5):

1. Friday, July 31st: $5. Central Park – Meet at Conservatory Garden (105th street and 5th Ave.) at 9am.

x. Saturday, August 1st: No BIRD WALK
2. Sunday, August 2nd: 9:00 amCentral Park – Meet at the usual location: the Dock on Turtle Pond at 9 am. $5.
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The fine print: Our summer walks on Sundays meet at the Dock on Turtle Pond (approximately 79th street in the middle of the park). Look for Belvedere Castle and you have found Turtle Pond. Bathrooms are located at the adjacent Delacorte Theater (Shakespeare in the Park) – and are nice. We end our weekend Central Park walks at the Boathouse at about noon. On Fridays, we meet at 9am at Conservatory Garden, 105th street and 5th Avenue (just inside the main gates). There are bathrooms open year-round at Conservatory Garden, and that is good. Easiest way to get there by subway is to take the #2 or #3 train to 110th street and Central Park north. Then walk south along the east side until you reach Conservatory Garden. You can also take the #6 train to Lexington Avenue and 103rd street. Walk west for three blocks and then north by two. Finally, buses run up Madison Avenue regularly too. If you need better directions, just email or call (718-828-8262) – especially for how to get to the meeting location of the Saturday walks.

Most bird walks last about two to three hours in Summer, but feel free to leave at anytime, we won’t take it personally. We have an extra pair or two of binoculars to rent, so if you want to rent a pair, just call or email before the walk to let us know. Also, if you are thinking of purchasing new binoculars, ask us – we probably have used them, and we will let you know how to get them for the best price.———————————————————————————————
Here is what we saw last week (selected highlights) with some anecdotal notes and observations. Not all species we saw are reported here – we list the best:

Friday, July 24th (North End Central Park) – Lately winds have been more southerly, with seasonable temperatures (low to mid 80s) and humidity levels. Migrants, which drift to our area on northwest winds, have not been as common in the latter half of July as we would hope. Nevertheless, with an intrepid crew of birders including at least two NYC school teachers, we set off to find some lost migrants in the north end of the park. Our best luck was with a bird I have seen in migration at night atop the Empire State Building (in October!) – a Belted (Eastern) Kingfisher was our best find – it flew past us in the woodlands on the north side of the “Loch.” We thought we heard it at a distance, and a small nudge from the iPod (kingfisher call) immediately brought the bird to us – and it continued on its way southwest through the woods. By the way, Belted Kingfishers bred in Pelham Nay Park in the Bronx until the mid-1980s…These days they are rather uncommon migrants in our area, though 1-2 may take up residence in Central Park for several days to weeks in spring and then again beginning in late summer, but not every year. Also today we tracked down a pair of Carolina Wrens at the north end…This is very interesting to us: each year beginning in late July, there is a dispersal of Carolina Wrens into our area (perhaps even from other city parks) – and we believe some of them begin nesting in Central Park in August. We are still investigating this, and will have more to report in the coming weeks as we watch this pair at the north end. Finally, no sign of The Hairy Woodpecker pair today, nor the lone White-breasted Nuthatch we had been seeing near the Blockhouse. Our best wishes to Emily Driscoll who is off to Iceland (and Grad School at NYU in film – science documentary.

Sunday, July 26th (Central Park,
Ramble area)
– With the hope of late summer migrants, off to the Ramble we went. For quite a while we had to be content with a Green Heron seen at Turtle Pond by all, and a House Wren seen by two. From the terrace of Belvedere Castle we spotted not one but two flocks of migrating Red-winged Blackbirds/Common Grackles (mixed) and a female Wood Duck (Carinne Mitchell – off to Cape Cod!) in Turtle Pond. From there we headed to the Ramble in the hopes of finding one of the recently released Eastern Screech-owls (no luck but we are not worried); instead we tracked down some migrants, all in the same area: The Point. From the rocky overlook near the Oven, we pulled in two Northern Waterthrushes (Thanks Sandra Critelli), and a few House Finches feeding on the last of some Mulberries. At the end of the Point, we pulled in another Northern Waterthrush and a Yellow Warbler, a Warbling Vireo, and surprisingly, a pair of very moulty Black-capped Chickadees. At Warbler Rock, we found a just fledged Grey Catbird, and learned that the Red-bellied Woodpeckers are not as aggressive toward intruders now than they were just 2-3 weeks ago. As per the suggestion for Regina Alvarez, we looked for and found a saprophytic native wildflower that grows on its own in Central Park: Indian Pipe (Monotropa uniflora). There were many clumps of this all-white plant that gets its nutrients not from photosynthesis but rather, directly from the roots of trees, particularly oaks on whose roots it likes to grow. Look for it in the area of the bird feeders. Finally, in prior years, we would recommend viewers to head to Turtle Pond at night to see this bird. foraging along the surface for fish. This year the pond is covered with Duckweed (Lemna minor), the smallest flowering plant in the world. Instead the skimmers have shifted their nocturnal foraging to The Model Boat Pond and The Reservoir….Though you can see them until about 9am on foggy mornings there too.

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