Sunday, December 06, 2009

A Raptor's Failed Nest?

I took this photo last weekend during a walk along the Delaware and Raritan Canal between Landing Lane and Demott Lane. Seeing that pile of branches near the top made me wonder how they got up there. I could think of three possibilities:
  1. The river deposited them during a flood. This sometimes accounts for strange accumulations of branches along shorelines. However, it seems the least likely explanation in this case because the towpath here is about 20-30 feet about the river and the branches are another 20-30 feet above the towpath.
  2. The branches fell into the crotch from higher in the tree or from other trees. This is plausible since branches often get caught in trees when they drop off. Even large branches can get caught and hang for quite some time. In this case, it is not clear where the branches would have fallen from, since they are lodged pretty close to the top of the canopy, and most of the higher branches seem smaller in diameter than the larger ones in the crotch.
  3. A raptor started to build a nest and then abandoned it. There are three possibilities here: Bald Eagles, Osprey, and Red-tailed Hawk, all of which breed in the area and all of which build large stick nests near the tops of tall trees. The trouble with this explanation is that some of the branches seem very large even for an eagle to carry.
So I am not entirely sure how that pile of branches ended up at the top of a tree.  I lean towards that, mainly because of the lack of a clear source for the branches to have fallen there. This pile also seems a bit too neat. Usually when I see suspended branches, they lie at various angles, whereas this batch seems to be stacked in a pile.

I could see a story of this pile unfolding as follows. A large raptor sees the tree as a suitable nesting spot, with the necessary height and access to hunting grounds and starts building. While still working on the nest, the raptor is disturbed by too many passersby on the canal towpath, which is heavily used by walkers, joggers, and cyclists, even in colder months. So the pair abandons the site and either does not breed or builds a new nest somewhere else. Of course, that is a hypothetical scenario, and I am not sure if I could prove it.

    Speaking of local birds, as of yesterday there was a Gray Catbird lingering in Johnson Park near where the bicycle path crosses under the railroad bridge. It is surprising to see a catbird this late in the season; usually when they do linger in this state they stick to coastal areas where the temperature is more moderate and insects are more plentiful. However, we have had a rather mild autumn so far. Our first winter storm of the season occurred just yesterday. I hope it sticks around for a few more weeks, so we can record it for the CBC.

    Other birds in Johnson Park included an adult male Merlin, perched near the zoo. I have seen Merlins pretty consistently in this area of the park over the past few years. It must offer them a good hunting ground. Waterbirds included a small flock of Buffleheads, three Common Goldeneye, and a Hooded Merganser.