Supposed Periodicity of Redpoll, Carduelis Sp., Winter Visitations in Atlantic Canada
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Supposed Periodicity of Redpoll, Carduelis sp., Winter Visitations in Atlantic Canada ANTHONY J. E RSKINE 1 and REID MCMANUS , J R.2 116 Richardson Street, Sackville, New Brunswick E4L 4H6 Canada 2657 Royal Road, Memramcook, New Brunswick E4K 1X1 Canada Erskine, Anthony J., and Reid McManus, Jr. 2003. Supposed periodicity of Redpoll, Carduelis sp., visitations in Atlantic Canada. Canadian Field-Naturalist 117(4): 611-620. Redpoll (primarily Carduelis flammea ) data from the New Brunswick–Nova Scotia border region were reviewed in the context of alleged biennial periodicity of irruptions south of their breeding range. Long-term records by the authors suggested a number of departures from visitation in alternate years. Three local Christmas Bird Counts (CBCs) spanning the last 41 winters supported the less-than-regular pattern shown by individual observations. CBC redpoll data from across the Atlantic Provinces revealed annual redpoll visitations across southern New Brunswick, where the largest regional counts (adjusted for observer effort) usually occurred. Visitation to Prince Edward Island, Nova Scotia, and Newfoundland was less frequent, and patterns there were often obscured by scarcity of CBCs with both long-run coverage and redpolls. Examination of those data in relation to varying food availability suggested that irregular abundance but near-annual occurrence of redpoll visitation explains observed observations better than attempts to find periodicity in their irruptions. Key Words: Common Redpoll, Carduelis flammea , Atlantic Provinces, winter, irruptions, periodicity, food availability. Redpolls (here discussed as Carduelis flammea; C. and limited seasonal sampling by CBCs. Hochachka hornemanni is rare – and under-detected – in our et al. (1999) used data from Project FeederWatch, region) breed in the subarctic all around the northern which partly avoided those limitations, but their paper hemisphere. Their occurrence south of the breeding (mainly using FeederWatch data for one winter, 1993- range varies between years and areas, some northern- 1994) did not address periodicity directly. They con- wintering areas holding redpolls in most years, whereas cluded that some redpoll movements occur every year, more southern areas have them less frequently. so these should be viewed as irruptive migration rather Several publications discussed “biennial periodicity” than nomadism. They acknowledged that “migration” in Common Redpoll movements to their winter ranges, in redpolls – unlike that of typical migrants – does not but seldom defined unambiguously what they meant by often link breeding areas to the same wintering areas periodicity. The most usual pattern featured southward each year. irruptions mainly or entirely in winters starting in odd- Larson and Bock (1986) examined redpoll CBC data numbered years, but such movements varied greatly – over a longer period (1901-1980), and concluded that in size and distribution – between areas and years. “the pattern and synchrony of (redpoll) eruptions… can Given biological variation, that was to be expected, but decay and reform over long periods of time and that one was left wondering what each author considered such patterns were especially weak between 1921 and as periodicity. 1950…”. Their graphs also showed some departures Kennard (1976) used banding totals from 1955-1972, from a biennial pattern in earlier and later time periods. mostly in the northern USA in winter and early spring. Variations in distance and numbers in redpoll move- Bock and Lepthien (1976) used Christmas Bird Counts ments generally are assumed to be food-driven. Evi- (CBCs), in early winter, from 1962-1971, in USA and dence of this is circumstantial, and we have no new southern Canada, but included very few (if any) from data on it. Southward movements presumably are trig- Atlantic Canada. Troy (1983) examined banding gered by food shortage in breeding areas, and contin- recaptures (none mapped as to or from the Maritimes) ue until food – in the east, especially seeds of birches for periodicity, distribution, and return to areas used or alders (Betulaceae) – is found in sufficient quantity earlier; Brewer et al. (2000) reviewed larger samples to attract transient flocks (Newton 1972), which often of band recoveries – but still none from the Maritimes are large. Large seed crops of those tree/shrub species, – for distribution. Houston et al. (2000) cited banding in breeding and northern wintering areas, occur more data (1960-2000) and CBC data (1956-2000), in Sask- or less biennially (some references given by Kennard atchewan and Manitoba, but focused on the (at Saska- 1976, and Bock and Lepthien 1976), but northern data toon) exceptionally large irruption of 1999-2000. Those are scanty where human populations are sparse and data-sets were judged to support “biennial periodi- economic importance of those trees is slight. Redpolls city”, to varying degrees. feed on those seeds (where present), but we know Hochachka et al. (1999) reviewed earlier studies, little about relations between levels of seed-crops of noting limited geographic distribution of banding effort those trees and numbers of the birds. Until studies are 611 612 THE CANADIAN FIELD -N ATURALIST Vol. 117 done on this, the role of food-sources in irruptions is area were easily distinguished from times when no only a working hypothesis. redpolls were seen. Variations in geography produce many departures Three local CBCs, near Sackville and Cape Tor- from strict latitudinal zonation. Temperature isotherms mentine, New Brunswick, and Amherst, Nova Scotia, in summer dip steeply across Canada from northwest all with annual coverage 1961–present, provided local to southeast; redpolls breed in the subarctic zone of comparisons. Selected CBCs elsewhere in New Bruns- Alaska and Yukon at latitude 60-70°N (Godfrey 1986), wick, Nova Scotia, Prince Edward Island, Newfound- but average 10° farther south from northern Ontario land – not including Labrador (see Figure 1 and Ap- east to Labrador (Todd 1963; Cadman et al. 1987; pendix 1 for CBCs used and locations) – extended the Gauthier and Aubry 1996). Redpoll winter range in picture geographically. Only CBCs with near-annual the prairie provinces follows the north edge of tree- coverage for ~20 years or more, and with redpolls less prairies southeast from 54°N in Alberta to 50° in reported in 10+ years, were used. Long-run counts Manitoba (e.g., Smith 1996), fanning out into wooded that rarely or never reported redpolls were ignored, areas farther southeast (e.g., Cyr et Larivée 1995). as were CBCs surveyed in <20 years. Most data were East of longitude 65°W much area between latitude taken from regional publications – N.B. Naturalist 47° and 50°N is occupied by the Gulf of St. Lawrence (earlier Nature News ), Nova Scotia Birds (earlier N.S. and connecting bays and channels, offering no habitat Bird Society Newsletter ), Island Naturalist (Prince for redpolls – which in Atlantic Canada must winter Edward Island), and Osprey (Newfoundland); Audu- farther north or farther south. bon compilations were much less complete for this Weather patterns also vary geographically. Owing to region, and duplicated only parts of coverage pub- the convergence, east of 65°W, of west–east and south- lished locally. west–northeast storm tracks (Bryson 1966), weather Because effort deployed on CBCs varied greatly in Atlantic Canada is more unsettled at all seasons (mostly increasing over the study period), all redpoll than farther west (AJE, personal observation). That counts reported were adjusted (roughly) to “counts probably influences year-to-year variation in habitat per 10 party-hours”. This made direct comparisons suitability for redpolls. Thus, redpoll occurrence pat- easier between counts with many vs. few observers. terns likely differ between Atlantic Canada and more The proportions of zero counts (absence, vs. presence, western parts of their range in North America. of redpolls) often seemed as informative as maxi- Our field data on redpolls in southeast New Bruns- mum (or modal) counts, as a few large counts were wick and adjacent Nova Scotia, together, spanned long- reported in years when most CBCs found no redpolls. er time-periods than databases used in other studies Geographic patterns in Atlantic Canada CBC red- cited (except Larson and Bock 1986), in a region from poll data encouraged dividing that data-set, for some which few or no data were available to earlier workers. comparisons, among seven sub-regions (see Appendix Our observations were supplemented by data from 1 and Figure 1 for CBCs in each sub-region): many CBCs in the Atlantic Provinces, to explore occur- • N–NB: 6 CBC circles in New Brunswick north rence or absence of patterns over time. of latitude 46°40’N; • S–NB: 10 circles in New Brunswick south of Data sources and methods above, and north of latitude 45°20’N; Our field data-sets were based on opportunistic, thus • ScoNB: 5 circles in New Brunswick south of frequently irregular, coverage. McManus (McM) has above, and adjoining south (Bay of Fundy) coast; lived all his life in Memramcook, New Brunswick • Bord: 3 circles in New Brunswick–Nova Scotia (46°00’N, 64°33’W), where he studied birds since border area; these counts were discussed separ- 1928. McM noted every bird he saw some winters, but ately as “Local CBCs”, but generally showed his notes are missing for some other winters; work- occurrence patterns similar to those in S–NB; time commitments often limited his opportunities for • N–NS/PE: 6 circles, 3 in Prince Edward Island, observing and recording data. Before 1940, he seem- 3 in east Nova Scotia (including Cape Breton ingly did not recognize redpolls by their calls, so his Island) north of latitude 45°15’N; field notes provided information on incursions mainly • S–NS: 7 circles in Nova Scotia south and west in 1940–74. Gaps in his observations or note-keeping of above; sometimes obscured local status of redpolls in the • INF: 7 circles in insular Newfoundland. 1940s and 1950s. Erskine (AJE) lived in Sackville, New Brunswick Results (45°54’N, 64°22’W), in 1960-1968 and 1977–present.