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Friday, February 08, 2013

Ravin' About Corvids

The experience that sparked my interest in birds and birdwatching was seeing my first urban Red-tailed Hawk. It was a fairly random sighting. My wife and I were taking a walk in Brooklyn's Prospect Park when I noticed a large bird of prey perched low and out in the open in a deciduous tree. As we were watching it a noisy flock of crows arrived on the scene and attempted to chase the raptor away. I soon learned that this is called "mobbing" behavior,  pretty typical of crows when they encounter a potential threat. From that point on, whenever I went in search of our local hawks, I found that listening for crows usually made quick work of it.

Crows, who are members of the family corvidae, are generally considered by biologist to be highly intelligent animals. When mobbing a raptor, they work cooperatively with each individual taking a turn diving at the interloper while the rest of the "murder" stands by as backup.

During my early days of birding in Brooklyn, American Crow populations around the city dropped off considerably due to the effects of West Nile Virus. That means there is a lot less harassing of the local Red-tailed Hawks. I'm not a scientist, but I'd imagine that the decline in crows have contributed to the breeding success of our city hawks. There are now multiple nesting pairs in each of the boroughs. This brings me to the point of this posting and a potential turn in the lives of our local Red-tailed Hawks.

Over the past few weeks there have been scattered reports of Common Raven sightings around Brooklyn and the rest of the city. Ravens are sort of like American Crows on steroids. They are much larger (2.6 lbs. average versus 1 lb. average) and, studies have shown, extremely smart. Historically, they were found throughout New York State. According to "Bull's Birds of New York State":

"The raven is thought to have been widely distributed over the state before the virgin forest was eliminated, but it had become very scarce in the 19th century, and Eaton (1914) reported it restricted, in constantly diminishing numbers, to the Western Adirondack region."

Their numbers appear to be rebounding, however, and not just in rural areas. For several years a pair has successfully nested in Queens, not far from Forest Park. With three recent confirmed sightings of raven in Prospect Park and Green-Wood Cemetery, last weekend Heydi and I went in search of one. We headed to Green-Wood.

We walked the ridges and valleys of Green-Wood for nearly 2 hours without hearing even a distant "croak" from this huge corvid. We did manage to locate a small flock of White-winged Crossbills and several other winter songbirds, but nothing out of the ordinary. When it was time for me to head home I decided to follow Dell Avenue down into Forest Dell. The path there is lined with sweetgum trees and a nice mix of songbirds were feeding on the spilled seeds below the trees. Dell Avenue is a long, gradual decline with steep ridges on either side. We were nearly at the bottom of the road when I heard the deep, croaking "cr-r-ruck, cr-r-ruck" of a raven. It sounded like it was coming from the south-west, near Cedar Dell. Heydi and I bolted up a steep ridge and ran towards Cedar Dell. The sound had stopped. We scanned the trees at the opposite side of the small glen for a few moments, then I saw a huge, black bird fly a short distance from a conifer on Walnut Hill into a tuliptree. He made a deep croaking sound. Right behind him was a Red-tailed Hawk in hot pursuit.

Ravens are opportunistic animals. They will eat just about anything. I have no idea if they ever prey on young Red-tailed Hawks, but to see our urban top-of-the-foodchain creature suddenly threatened by another bird gave me pause. I've seen red-tails fighting with Great Horned Owls over a nest site, but for the most part the owl and hawk usually just ignore each other. Our cemetery Red-tailed Hawk clearly did not want this raven in the neighborhood. As we watched, a second, immature Red-tailed Hawk joined in the fight. The two hawks chased the raven back and forth between the trees at Cedar Dell and Walnut Hill. After a few minutes the hawks prevailed and the raven mumbled a few words before disappearing in the direction of 20th Street.

For a short time, the tables had been turned on the Red-tailed Hawks. Where they are normally the top predator being periodically hounded by crows, they seemed to be instinctively intimidated by the raven. I use the word "instinctively" because I'm guessing that most of our born and raised NYC Red-tailed Hawks have never crossed paths with a raven. It will be interesting to see how this situation evolves, especially if the ravens end up nesting near the cemetery.

If you'd like to read about ravens, Berntd Heinrich authored the book "Mind of the Raven: Investigations and Adventures with Wolf-Birds", in which he adopts ravens in order to get a closer look at their behavior.


Ryan M said...

Those are interesting observations, Rob. Indeed, growing up on Long Island I encountered many more crows than I see lately. I wish you divulged what date you saw the hawk and the raven battle. I've read a few reports now of these two fighting in the area recently and in fact I came across a pair quarreling on February 4th. The pursuit began from the northern most parts of Green Wood...perhaps even from outside of its boundaries...and continued south into the heart of the cemetery. I did not get to see the two grappling on the ground, as I imagined I might, but did see the raven a little later flying around without a raptor on its heels. These pics I took are not the greatest, but they document the aggression and help to show just how massive the ravens really are!

Rob Jett said...

Ryan - My raven-hawk encounter was on Superbowl Sunday. I tried to check out your raven pics, but the link didn't work.

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