30 Correlations Among Winter Finch Numbers at Ottawa, 1958-1983 by Alex Mills

In Ontario, winter finches allow accurate predictions of what comprise nine seed-eating species: sort of winter it will be. The Evening Grosbeak (Coccothraustes formula for estimating the timing vespertina), Pine Grosbeak of flights is even more elusive. In (Pinicola enuc!eator), Purple some years redpolls arrive in Finch (Carpodacus purpureus), numbers in southern Ontario by Hoary Redpoll (Carduelis early November, while in others hornemanni), Common Redpoll (C they do not appear until March. jlammea), Pine Siskin (C pinus), After the spectacular numbers of American Goldfinch (C tristis), Red Purple Finches, Pine Siskins, and Crossbill (Loxia curvirostra), and both crossbills in the winter of White-winged Crossbill (L. leucoJr 1984--85, I found myself tera). All but the Purple Finch and wondering about the synchrony of the American Goldfinch are winter finch flights in Ontario. To typically northern breeders in what extent do large numbers of eastern North America, summering one species coincide with either in the coniferous forests and even large or small numbers of another? beyond in the case of the redpolls. To find out, I assembled data Winter numbers of Purple Finches from the Ottawa-Hull Christmas and goldfinches in the south vary Bird Counts for the period 1958­ each year, and the numbers of the 83 (published in Audubon Field grosbeaks and northern Carduelis Notes and American Birds). finches can vary dramatically. Ottawa was chosen because it Crossbills, of course, are famous receives thorough coverge, because for their sporadic irruptions. it often has good fmch numbers, and People have been trying to because it is essentially at the north­ determine the factors governing the south interface that extends along the irregular patterns of occurrence of south edge ofthe shield. Freedman winter birds for some time. It is and Riley (1980) have shown that generally agreed that irruptions are some winter finch species have dependent on high numbers of established "modern" population birds and poor food crops (Bock levels only since the mid- to late and Lepthien 1976), but knowing 1950s, and so I selected the period these factors does not seem to beginning in 1958.

Alex Mills, 1007-27 Cardigan St., Guelph, Ontario NIH 7V6

ONTARIO BIRDS APRIL 1986 31

For each species for each year, I negative (high numbers of one determined numbers ofindividuals species coinciding with low counted per party hour, as numbers ofthe other). Thus, for recommended by Bock and Smith example, Hoary Redpoll and (1971). I then looked at each Common Redpoll show a strong species pairing (36 in all) and positive relationship while Evening calculated the extent to which the Grosbeak and Purple Finch show numbers for each pairing varied a moderate negative one. together. I did this by using For the most part, the significant correlation analysis, as described results make sense. Goldfinches in most statistical texts (e.g., Sokal and Purple Finches, the two 1973). In short, coefficients of species that regularly breed in both determination derived from the the south and the north, correlate analysis and indicated as positively with each other and percentages reveal to what extent negatively with Evening Gros­ high numbers of one species beaks, a more exclusively northern correlate with either high or low breeder. Evening Grosbeaks also numbers of another. correlate positively with Pine Following standard statistical Grosbeaks and Common Redpolls, procedures, any percentage less two other northern species, and the than 15.1 is not considered Hoary Redpoll-Common Redpoll significant. Using this value, only correlation is certainly no surprise. seven ofthe 36 pairings were The only perplexing result is the significant. The results for the positive Purple Finch-Red seven are presented in Table 1. Crossbill correlation; winters of The numbers indicate the strengths large numbers ofPurple Finches at ofthe relationships and the +/­ Ottawa have also tended to be signs indicate whether the winters of large numbers of Red relationships are positive (high Crossbills. That 29 of the 36 numbers of one species coinciding pairings (including all those of with high numbers ofthe other) or Pine Siskin and White-winged Table 1. Significant correlations among winter finch numbers based on Ottawa-Hull CBC data, 1958-1983. All other species pairings (29 in number) had percentages of less than 15.1, making them statistically non-significant. STRENGTH OF RELATIONSHIP AS SPECIES PAIRING +/- AS PERCENTAGE Evening Grosbeak - Pine Grosbeak + 23.6 Evening Grosbeak - Purple Finch 21.3 Evening Grosbeak - Common Redpoll + 22.6 Evening Grosbeak - American Goldfmch 24.0 Purple Finch - American Goldfinch + 24.4 Purple Finch - Red Crossbill + 20.9 Common Redpoll - Hoary Redpoll + 48.7 VOLUME 4 NUMBER 1 32

Crossbill) reveal strict indepen­ Crossbills cycled together. Their dence indicates considerable data, and the data presented here, autonomy of response to the suggest that Lack's claim is not factors that determine movements. always true. This method of analysis is subject to some ofthe problems Literature Cited encountered in other CBC data Bock, C.E. and L. W. Lepthien. studies. Weather factors and 1976. Synchronous eruptions of accuracy of identification and boreal seed-eating birds. Amer. enumeration are two obvious ones. Nat. 110:559-571. Parker (1973) clearly showed that Bock, C.E. and R.B. Smith. 1971. Pine Grosbeaks moved through An analysis of Colorado southern Ontario over the duration Christmas Counts. Amer. Birds ofthe 1971 CBC period; 25:945-947. obviously, the date of each 1971 Freedman, B. and J.L. Riley. count in southern Ontario 1980. Population trends of influenced the Pine Grosbeak various species of birds tally. This leads me to wintering in southern Ontario. acknowledge that what is true in Ont. Field BioI. 34:49-79. late December may be very different from what is true in, for Lack, D. 1954. The natural instance, late February. Perhaps regulation of animal numbers. Clarendon, Oxford. 343 pp. my results can be applied no further than Ottawa for the period Parker, M 1973. Influx of Pine used! Grosbeaks into southern Lack (1954) claimed that Ontario and adjacent New York different species irrupted inde­ State, December 1971. Amer. pendently of each other. Bock and Birds 27:839. Smith (1971) plainly showed, Sokal, R.R. 1973. Introduction to however, that Colorado popula­ biostatistics. Freeman and tions of Red-breasted Nuthatches Company, San Francisco. (Sitta canadensis) and Red

Eastern Kingbird PHOTO: R.D. McRae

ONTARIO BIRDS APRIL 1986