Thursday, August 30, 2012

Purple Martins, what do they do here?

[Click on image to see larger version. Copyright 2010 by Tony Leukering.]

Purple Martin is a common and well-loved species that breeds in Cape May in widely scattered colonies in human-provided condominiums. They prefer box sites that have extensive uncluttered space around them and, typically, well above the ground. The very first migrants of spring are usually spotted in early March, though this spring saw the area's first February records, the first in Cape May Point on the 26th. Regardless of how early the first migrant may appear, however, local colonies are not attended, often, until early April, probably because of the depressing effect on spring of all that surrounding cold water.

However, the focus of this essay is on what the species and individuals do here in fall. The Mauricetown-area (Cumberland Co.) staging area is well known, with martins starting to concentrate there in numbers in July and continuing to accumulate into August, with counts often exceeding 35,000 (this year's counts were through the roof, from what I understand). But, again, I am more immediately interested in what they do in lower Cape May Co.

Many fall mornings, I wake up to the same conundrum, go to the Higbees Beach SWA dike and join in the fun there counting the morning flight (and not really having to have to do any actual counting), or stay at my north Villas home and count the same flight line from my house, with the concomitant possibility of new yard birds, but, with the self-imposed duty to actually count everything. And, for anyone that thinks that the task of the morning-flight counter -- other than identifying everything -- is not that hard, come stand under this flight when it's scattered over an east-west distance of a quarter-mile, with birds at a large variety of altitudes and see what you think.

Anyway, the Purple Martin flight at my house has had my attention for a few years, now, and I still do not really understand it. From the efforts of many on Cape Island, we have a general sense of how birds arrive to take part in the nearly daily phenomenon of fall northbound morning flight over Higbees, but that general sense is for species in general, but particularly for small, nocturnally migrating passerines. Our understanding does not seem to stretch to all diurnally migrating birds, and swallows, particularly Purple Martins, seem to do something quite different. That is because, nearly every time that I count a big flight of martins at my house, the folks at the Higbees dike did not experience the same flight. This difference between two otherwise similar sites that are just 5 miles apart (as the Peregrine flies) at a bearing of just east of north (14 degrees) has had me flummoxed, particularly as the flight is otherwise quite similar.

Yesterday provided, unknowingly to me, a chance to prove that difference. I made the decision the previous night to go to the dike, getting there before sunrise and had a wonderful morning there (see the details in Cameron Rutt's post). When Purple Martins starting flying by us, because the morning-flight count does not tally them, I had a clicker ready in my pocket and started counting them. By the end of the flight, I had counted 112, not a bad count for so late in the species' occurrence time here.

This morning, Jim Dowdell called me to ask me whether I had counted Purple Martins at the dike (apparently, some know me far too well!), because he had watched a huge flight of them go over his house yesterday morning. Jim lives just a bit north of equidistant between my house and the Higbees dike in south Villas; his house, too, is right under the flight line. Jim watched "thousands" go north past his house on the Delaware Bayshore yesterday and, presumably, those birds kept going north past my house, too.

So, Purple Martins (and, I think, other swallow species) deal with the Cape May peninsula quite differently than do many other passerine species. What we need to figure this out, is to have folks look from other places (e. g., the West Cape bridge) to see where those thousands of Purple Martins are south of Villas before they hit the Bayshore and turn north, because it is decidedly somewhere not as far west and south as the Higbees Beach SWA dike.