Beginning in February 1996, a team of field ornithologists has been studying winter bird populations on Block Island, Rhode Island, by bracketing the traditional Christmas Bird Count (CBC) with similar counts around 10 November (Veterans Day Count, VDC) and 20 February (Presidents Day Count, PDC). Block Island was chosen because of its isolation from the nearest neighboring landmasses (the RI mainland and Long Island) and because it lacks (or nearly lacks) resident populations of many landbirds that are common year-round in these neighboring areas. Thus, the variable occurrence of such species on Block Island is easily interpretable as migration or dispersal, even in species for which such behavior is difficult to measure, or even discern, on the mainland (Downy and Hairy Woodpecker, White-breasted Nuthatch, etc.). The target date of the November count was chosen to fall later than the bulk of stereotyped long-distance migration by most nocturnal-migrant landbirds and many diurnal migrants, too. Similarly, the target date of the February count was chosen as deep into the winter as possible but still prior to the advent of stereotyped northbound migration in most species of landbirds. The primary original goal was to evaluate the over-winter survival or persistence of many “half-hardy” landbird species that, although near or beyond the normal limits of their winter ranges in southern New England, are regularly observed there on the mid-late December CBCs. Another question was whether the diminution of such species between December and February could be attributable, at least in part, for some species in some years, to over-water dispersal, in addition to mortality. Within a few years we recognized that all of the half-hardies that are most numerous on the CBC typically persist into mid-late February, and that their reduction in abundance is often no greater than among the most abundant landbird species wintering in the same habitats. We also noted a strong tendency for many species, but especially the half-hardies, to increase in abundance between November and December, proving a general capacity of such birds to undertake major movements long after their periods of “normal” migration. This latter finding suggests that such movements are at least possible later in the winter and might in fact contribute, along with mortality, to the reduced abundance observed in February. Related to both of these goals was the important practical question of whether the timing of the traditional CBC is possibly too early in the winter to provide a reliable measure of winter abundance in many species. Our conclusion (at least in the early years of this now multi-decade project!) was a validation of the CBC for this site: abundance on the CBC accurately predicted abundance on the PDC, whereas abundance on the VDC varied wildly and did not predict abundance on the CBC. Finally, the extra data and context provided by the supplementary counts were intended to assist with studying long-term trends (for instance, related to climate change); as hinted above, insights have been gained on this question as well.
This year’s Presidents Day Count was conducted on 21 Feb 2022 by 17 observers in ten parties—significantly better coverage than usual (average seven observers in four parties). Note, however, that the 39.8 party-miles on foot exceeded the average of 27 to a lesser extent than implied by the other metrics, because extra effort is devoted to legwork in years with fewer participants. An unprecedented total of 95 species was recorded, with variety well distributed across seabirds, freshwater species, and landbirds. All but one of the notable misses involved species that are frequently missed on the PDC: Northern Gannet (seventh miss), American Coot (eleventh miss), and Bonaparte’s Gull (eleventh miss). Ruddy Duck, Pied-billed Grebe, Double-crested Cormorant, American Bittern, Great Blue Heron, and Belted Kingfisher resemble Coot in their tendency to vanish after hard freezes, so it was notable that all except for the grebe and kingfisher were tallied this year—all singles, except for three Great Blue Herons. Virginia Rail is somewhat less sensitive than the preceding, but this year’s total of six was remarkable for the date. Freshwater ducks that can tolerate short periods of freezing were conspicuous: Gadwall, Ring-necked Duck, and Hooded Merganser continued their trends toward increased abundance, two rare species were found (Blue-winged Teal and Redhead, both fourth occurrences), and various others were present in large numbers, even though frequently missed altogether (18 Snow Goose, 36 American Wigeon, and 13 Green-winged Teal). Had I been told ahead of time we would see four species of alcids, I could not have imagined we’d miss Common Murre, which has been recorded on all but two of the previous 17 PDCs. Razorbills were numerous, four Black Guillemots was more than usual, and a trio of Dovekies and a Thick-billed Murre were excellent finds. Horned Grebes were 22 times more numerous than on the CBC, when just one was tallied, continuing their dismal slide toward scarcity. A total of just 99 Red-breasted Mergansers was also consistent with their negative trend, but the also-declining Great Cormorant hung on this year, the total of 77 close to the long-term average of 79. Raptors were very well represented, perhaps not surprising given the overall diversity and abundance of landbirds. Thicket-dwelling landbirds almost always diminish in abundance from Dec to Feb, as measured by birds per party-mile on foot. This year, uniquely, many such species maintained their numbers or even increased in abundance, including numerous half-hardies. Furthermore, relatively few (compared to most years) increased between Nov and Dec. Among thicket birds seen on all three counts, only Winter Wren, Swamp Sparrow, and White-throated Sparrow showed the classic “half-hardy bump,” an increase from Nov to Dec followed by decline from Dec to Feb, that we’ve come to expect for many species in most years. It must be noted that this winter’s cycle (Nov 2021-Feb 2022) was highly unusual. The first interval (VDC-CBC) was strikingly open, with hardly any freezing and no snow, whereas the second interval (CBC-PDC) featured repeated bouts of severe cold (none very prolonged, though) and two significant snow storms. If one were to describe a year when cold-sensitive landbirds could remain numerous and widely distributed across southern New England through year’s end, and only later experience pressure to disperse to coastal thickets, this was the year—the only question being whether the severity of the end-January blizzard and subsequent intense cold were survivable at Block Island. Apparently they were. A Pine Warbler was the first ever for the PDC and a House Wren just the second. Six Virginia Rails made it through the bottom of the winter, and Yellow-shafted Flicker, sensitive to snow and cold, was more numerous than usual. Corrected for effort, the Feb abundance of Brown Thrasher, Hermit Thrush, and Fox Sparrow equaled that of Dec. Gray Catbirds increased 22% over Dec, whereas Eastern Towhee increased by almost 300%. This was not because the CBC was held on a bad day. The three count days (15 Nov, 16 Dec, and 21 Feb) were all favorable for effective bird-counting; all featured westerly breezes of comparable intensity and seasonably mild temperatures. Furthermore, detection rates were actually slightly higher in Dec than in Feb for the highly sedentary Carolina Wren and the highly mobile Myrtle Warbler, just slightly lower in Dec for Black-capped Chickadee, and almost identical for Song Sparrow. As noted above, White-throated Sparrow was more numerous in Dec than in Feb, so it is clear that the surprising abundance of many half-hardy species in Feb was not due to poor detection in Dec and better detection in Feb. This conclusion also demands that serious consideration be given to the seemingly preposterous idea that the Dec to Feb increases observed for Northern Mockingbird (65%), House Finch (94%), and Northern Cardinal (29%) might have been driven by large-scale, over-water dispersal in mid-late winter! The abundance of American Robin and Red-winged Blackbird (and also Killdeer, and perhaps some of the freshwater ducks) probably or certainly reflected northbound migration, but there is no body of evidence, however anecdotal, suggesting that species such as Catbird, Hermit Thrush, or Towhee migrate northward at this date. But perhaps the last statement must be qualified with “--yet.” All of the long-time participants in the winter counts agree that over the past 27 years fall migration has stretched further over our November count window, and spring migration over our February window. These questions await critical analysis, but I can offer one metric as illustration of how much the overall winter season dynamic has changed over the course of this study. As mentioned above, an early aim of the work was to validate (or not) the idea that the CBC was accurately measuring winter abundance. We concluded that it was, based in part on the relatively strong correlation in overall landbird abundance between December and February, and the absence of such a correlation between November and December. Over the first 14 years of the project, the Dec-Feb correlation was 0.76, which I think is remarkable, given all of confounding variation from count to count in personnel and weather. In contrast, abundance in November (presumably influenced by each year’s late fall migration) failed to predict abundance in December, just a month later (0.10). But this dynamic has broken down in recent years. Over the past 13 years, the Dec-Feb correlation has diminished by more than half (to 0.34) and is now exceeded by the Nov-Dec correlation (0.56). To state it plainly, the December count is now a late fall count, and the February count the truer measure of winter abundance here for most species. To conclude, I would like to express my deepest gratitude to all of the participants on this year’s PDC, including three people new to the winter count project. If one dates this project to the CBC preceding the first PDC, in Dec 1995, the count we just completed was the 80th, and the 75th for me. A total of 68 individuals have devoted 720 person-days to the counts, of which no fewer than 441 have been contributed by the 17 people participating this year. Shai Mitra Bay Shore, NY -- NYSbirds-L List Info: http://www.NortheastBirding.com/NYSbirdsWELCOME.htm http://www.NortheastBirding.com/NYSbirdsRULES.htm http://www.NortheastBirding.com/NYSbirdsSubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/nysbirds-l@cornell.edu/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L 3) http://birding.aba.org/maillist/NY01 Please submit your observations to eBird: http://ebird.org/content/ebird/ --