Curiously, statewide trends and recent Long Island trends stand in remarkably different relationship for each of the big black carrion-eaters under discussion.
When Griscom analyzed the status of Turkey Vulture in 1923, this species was common in the highlands of northern New Jersey but poorly distributed in mainland NYS and a rare visitor to LI, with most LI records from the western (e.g., Brooklyn) or eastern (e.g., Orient) ends. Over the remaining eight decades of the 20th Century, this bird underwent a vast northward expansion, spreading across most of mainland NYS--but retaining its LI status (scarce and irregular) with astonishing fidelity. Few birds of any kind showed such a static pattern on LI over the same period--but for a bird whose status changes so much nearby, this stasis is particularly remarkable. It has only been over the last ten years or so that Turkey Vultures have finally moved onto LI in numbers, including winter roosts and proven breeding. The lag between occupation of the adjacent mainland and dramatically increased occurrence on LI in this case was >50 years. The early history of Black Vulture in NYS was mostly as a vagrant to LI. Again, it's status on LI remained static for a century while the species made news elsewhere. In contrast to its relative, however, Black Vulture's northward expansion on the mainland lagged behind Turkey Vulture's by at least several decades, and its occupation of the Hudson Highlands and nearby parts of mainland NYS took place mainly in the 1980s and 1990s. This distinction is very important because Black Vulture's trend toward increased occurrence on LI, which prompted this thread, has occurred more or less simultaneously with Turkey Vulture's, in very recent years. The lag between occupation of the adjacent mainland and dramatically increased occurrence on LI in this case was about 15 years. As Kevin notes, Raven was once almost extirpated from the eastern United States and was no more than scarce wilderness specialist in NYS for the first two-thirds of the 20th Century. Its expansion over the last several decades has been spectacular, e.g., a 500% increase in occupied blocks between the two atlases. Like both of the preceding species, Ravens have made news on LI during the last few years. Unlike them, however, this trend followed immediately upon its occupation of adjacent mainland areas, with no perceptible lag at all. Another hulking black carrion-eater probably deservers mention here. Bald Eagle's inter-atlas surge in NYS makes Raven's seem downright paltry, its confirmed blocks increasing 6,000%! Statewide observers probably don't appreciate how oddly scarce this species remained on LI through most of the 20th Century, even as its status was changing so radically in nearby mainland areas. Admittedly, the broader trends for this species are far more complex than those described above, with regional breeding populations, those breeding far to the north, and also wanderers from the south each experiencing its own roller-coaster fortunes and contributing to LI occurrence. Even so, one gets the impression from reading the books that Bald Eagle's LI status didn't vary greatly from Griscom's time (1923) to Cruickshank's (1942) to Bull's (1964) to the late 20th Century (personal experience), except that it was probably even scarcer here during and after the DDT era (60s-90's). Although I know this doesn't do justice to this species' comnplex history, I can say without doubt that there has been an abrupt increase in the occurrence of Bald Eagles on LI and in RI during the last ten years, as compared to the 80s and 90s. Like all of the preceding, Fish Crow expanded as a breeder in NYS between the two atlases, but unlike any of the others, Fish Crow initially moved into southeastern NYS in an equitable fashion, occupying both the Hudson Valley and LI over a century ago. Given its ubiquity on LI throughout my own experience, I'm not sure if it has increased here very much over the past ten years, but my hunch is that it has increased at least somewhat. Fish Crow has expanded greatly in southern mainland RI over the last decade. Last, and perhaps most important from an ecological point of view, is the case of American Crow. It is very difficult to quantify the status of this abundant and truly ubiquitous bird, but the impacts of West Nile Virus in the early years of the past decade have been much publicized. Even giving due allowance to the difficulties of counting crows owing to vagaries of their local movements and roosting patterns, I'm convinced that this species is much less numerous today than ten years ago in the areas I know best--LI and southern mainland Rhode Island. In these areas, at least three long-standing roosts of +10,000 birds simply seem to have vanished. Even if many of those birds have moved a few tens of miles away or shifted to a more dispersed distribution, the following facts are hard to explain except as reflective of population reduction: on the Napatree CBC (sw mainland RI) totals have fallen short of 100 in five out of eight years and never exceeded 160 since 2002. on the Captree CBC (central south shore of LI), totals averaged 707 (1991-2000) vs. 197 (2001-present), and just 164 2003-present. on the Southern Nassau County CBC (western south shore of LI), totals averaged 1,062 (1991-2000) vs. 431 (2001-present), and just 197 2003-present. I am aware that correlation does not prove causation, but I would argue that, at least on LI and in southwestern RI, dramatic local increases in Turkey Vulture, Black Vulture, Bald Eagle, and Fish Crow have coincided perfectly with apparent reductions in numbers of American Crows--despite the otherwise highly disparate regional trends shown by these increasing species. I would also caution against using behavioral dominance as a proxy for ecological competition. Black Vultures dominate Turkey Vultures at kills, but this doesn't translate into a consistent pattern of numerical superiority, as these two species share vast portions of their ranges, with every conceivable local balance of power represented in multiple places. A truer test of competition is to selectively remove one species from an area and then observe what happens to the abundance of potential competitors. If American Crow numbers have, in fact, diminished by 70-80% on LI and in southern RI, this ought to translate into a vast increase in available carrion, owing to the sheer abundance of this species compared to the others--plausibly enough of an ecological shift to tip the balance for species that have been waiting coyly on LI's doorstep for as long as 50 years or more. To finish with an anecdote that illustrates how much things have changed, it was not until 8 January 2008 that I first saw a Raven in Rhode Island; on 24-25 January 2009, Patricia and birded around southern RI and recorded eight Ravens at four sites before we finally encountered our first American Crow! Shai Mitra Bay Shore ________________________________________ From: [email protected] [[email protected]] On Behalf Of Kevin J. McGowan [[email protected]] Sent: Wednesday, March 24, 2010 10:26 PM To: NYSBirds Subject: RE: [nysbirds-l] Brooklyn BLVUs Interesting things to ponder. But it is appropriate to point out that Common Raven has undergone a HUGE range expansion in New York (and elsewhere) in the last 20 years, as evidenced by the recent NY breeding bird atlas data, well before the appearance of West Nile Virus (WNV). The raven went from being a “wilderness” specialist to being present in 35% of the blocks in the state. It was missing only from the lowlands of the Ontario plain and the coastal regions. I believe that in the raven species account I suggested that it would soon reach those areas too. The raven trend is bigger than New York, occurring before WNV, and in areas that were not really affected by the disease. Not to say that WNV couldn’t play a role, but ravens don’t seem to have much regard for crows anyway, pretty much doing whatever they damned well please. Fish Crows, on the other hand, might be taking advantage of the American Crow die-back. They seem to do pretty well in areas with American Crows, but they definitely are submissive and might be kept out of potential breeding areas that the WNV effect would open up to them. (Fish Crows are only half as susceptible to WNV as American Crows.) Black Vultures also have been increasing in NY for a while (not present at all in the 1980-85 atlas). But as the Atlas species account (ahem, also written by me) points out, they have not really expanded out of the rocky southeastern part of the state since moving into there. Despite some criticism (!), in the Atlas accounts that I wrote I attempted to speculate on what past trends might mean for future distribution patterns. Black Vulture was a toss up. Its history indicated that it should continue spreading, and its wide habitat tolerance and huge distribution outside the US would suggest that it should be capable of inhabiting the entire state. And yet, after it appeared here it never seemed to go outside the realm of the rock-slide caves of the Catskills and lower Hudson Valley. It could, it should, but will it? For anyone who thinks that bird distributions are static and well known, PLEASE go buy a copy of The Second Atlas of Breeding Birds in New York State (Cornell University Press). (And I do not get any royalties or kickbacks from shilling this book either. It’s just a great resource, IMHO.) Kevin **************************************************** Ithaca, NY 14850 [email protected]<mailto:[email protected]> http://birds.cornell.edu/crows/ Think green before you print this email. -- NYSbirds-L List Info: http://www.NortheastBirding.com/NYSbirdsWELCOME http://www.NortheastBirding.com/NYSbirdsRULES ARCHIVES: 1) http://www.mail-archive.com/[email protected]/maillist.html 2) http://birdingonthe.net/mailinglists/NYSB.html 3) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L Please submit your observations to eBird: http://ebird.org/content/ebird/ --
