Are Pine Grosbeaks Increasing at Bird Feeders in Ontario?
Total Page：16
File Type：pdf, Size：1020Kb
87 next month, then less frequently, certainly possible there were other but in larger numbers (up to 30), visits that went unrecorded. for another month. In that time, Bill Walker my notes mention visits to the Deep River, Ontario feeder only four times, the first on 31 January (two birds), but it is Are Pine Grosbeaks Increasing at Bird Feeders in Ontario? by Erica H. Dunn A suggestion has been made that Methods Pine Grosbeaks (Pinicola enucleatm-) OBFS counts were obtained from may now be using bird feeders to a the organizing body, the Long greater degree than in the past Point Bird Observatory. Each year, (Pittaway 1989). Most of the 400-500 people across the province supporting observations, however, tallied the birds observed at their were from a restricted area between feeders during a one to two day Lake Simcoe and Algonquin Park. period, every second week from Here I look at the entire province, November to April. Observers for the period 1976-88, using data recorded the peak count ofeach from Christmas Bird Counts species seen in the observation (CBCs) and the Ontario Bird period. For further details, see Feeder Survey (OBFS). These Dunn (1986). resources allow us to say whether OBFS counts and CBCs were Pine Grosbeaks are now attending divided into three regions: feeders in greater numbers relative Southern Ontario extended to their abundance in the wild (as roughly to a line through Lake measured by CBCs) , as well as to Simcoe to Belleville, including the comment on the hypotheses Bruce Peninsula, Barrie and proposed by Pittaway to explain his Peterborough. Central Ontario was observations. defined as the area between the South and a line north ofParry Sound that passes through Erica H. Dunn, 30 Davidson Road, Aurora, Ontario L4G 2B1 VOLUME 7 NUMBER ~ 88 Algonquin Park and east to counts with CBCs, OBFS data were Petawawa. Northern Ontario was taken from the fourth count period defined as the area north of the only, which is the one Parry Sound-Petawawa line (see corresponding most closely in date Dunn 1986). to CBCs. The proportion of all In analyses comparing feeder OBFS counts and CBCs from the province that were conducted in each of these regions was very Figure 1: Ontario Bird Feeder Survey similar for both types ofcounts results for Pine Grosbeak. (Dunn 1986). Solid lines show the average To determine whether a high n urnber per feeder for the proportion ofPine Grosbeak year (November through populations attended feeders at March), while the percent high population levels, multiple of all feeders visited on at regressions were conducted of least one of the ten count OBFS counts (average birds per periods is shown by dashed feeder) on CBC (average birds per lines. party hour) and CBC2 for each region and for the province as a 6..--------------, whole. If CBC2 dropped out of an 4. equation, the relationship between 80 the two counts was constant, while 2. eo if CBC2 remained, either increasing o or decreasing proportions of birds 40 a::: visited feeders at higher population w 20 ~ densities. o fTl w :::0 ~ .6.+-------------t-0 (') fTl Z Results and Discussion a::: ,4 ~ Although the Pine Grosbeak is rare uJ 40 a.. "TI .2 FTl at feeders in Southern Ontario, it is a::: 20 fTl w 0 quite common in the North ~ fTl 0 0 :::0 (Figure 1). It is the sixth most ::> ~------------i (J) z abundant feeder species there, 08 :5 w· (J) averaging 2.5 birds per feeder <.!) =i throughout the winter, and 4.9 ~ ,06 fTl w 8 0 birds at the 51 % of the feeders ~ .04 6 which are visited by the species at ,02 all. Pine Grosbeaks drop off 4 o dramatically at feeders in Central 2 Ontario, where Pittaway's 0 observations were made, and are even less common in the south. 76-7 ~ 82-3 85-6 8&-9 YEAR ONTARio BIRDS DECEMBER 1989 89 Numbers ofPine Grosbeaks at there are large n umbers in an area, feeders vary markedly from year to such that we see relatively higher year, as expected of an irruptive visitation rates in Central and cardueline finch, in parallel Southern Ontario during invasion throughout the province (Figure 1). years (Pittaway 1989). Regression There were no significant trends analysis of OBFS against CBCs, with year, despite the apparent however, showed a straight line increase in the north. Although relationship within each region. 1985-86 was a high year for Pine This means that fluctuations in Grosbeaks at Ontario feeders, it was CBCs were paralleled by changes in not as unusual as suggested by feeder counts, and that a constant Pittaway (1989), since similar proportion of birds came to feeders numbers had occurred before. at all population densities. These data suggest no change in On the other hand, ratios of feeder use over time, but to be OBFS to CBC numbers indicated certain, we have to compare feeder that a much higher proportion of counts to populations in general. birds in the north visited feeders Even though feeder visitation has relative to population size than did remained steady, a general decline so further south (Table 1). A in Pine Grosbeak populations regression of OBFS on CBCs for the would show that feeder visitation province as a whole indeed showed with respect to numbers in the wild that more birds visited feeders at had indeed increased. This was high population levels, contrary to checked by looking for trends in the result discussed previously for Ontario CBCs, the only available each region. At least in part, this index of total population size for may be an artifact of the data. CBCs the winter season. No significant are conducted under increasingly trends were found in CBCs over the severe winter conditons as one goes period 1976-88. I conclude that north. More of the birds tallied on feeder use relative to population CBCs there may actually have been size has also remained steady. counted at feeders, making the two Perhaps Pine Grosbeaks come to count types less independent than feeders in higher proportions when further south. Currently we are Table 1: Average OBFS abundance (fourth count, birds/feeder) and CBCs (birds/party hour) for Pine Grosbeak, 1976-77 through 1987-88 (1984-85 missing). Ontario North Central South OBFS 2.5 0.2 0.03 CBC 2.0 0.9 0.4 Ratio (OBFS/CBC) 1.3 0.2 0.08 VOLUME 7 NUMBER ~ 90 Table 2: Ten-year average OBFS figures for Pine Grosbeak and possible competitors at feeders. Abundance (A), percent offeeders visited at least once in season (%) and regional rank in abundance at feeders (R). Ontario North Central South A % R A % R A % R Pine Grosbeak 2.5 51 6 0.2 14 19 0.03 3 21 Evening Grosbeak 12.2 88 1 13.4 89 1 3.3 46 5 unable to separate individuals feeders in Northern and Central counted during CBCs at feeders Ontario than in the south and away from feeders, so this (Table 2). There was a negative possibility cannot be checked. correlation (P.=0.033) between Ifwe assume that there is at least Pine and Evening Grosbeak some tendency for Pine Grosbeaks numbers at feeders in the north to attend feeders more often in the (and no correlation elsewhere), but north than elsewhere, what could the same correlation was found for be the reason? One suggestion is CBCs. In other words, Pine that Pine Grosbeaks in the south Grosbeaks were more abundant in may have arrived from remote the north when Evening Grosbeaks regions where feeders are scarce, so were not, but any possible causal have not learned to use them realtionship took effect at the (Pittaway 1989). I can't address this population level, and not at feeders. possibility without banding data, If a higher proportion ofPine but the fact that Pine Grosbeaks are Grosbeaks really does visit feeders so common at feeders in Northern in the north than further south, the Ontario suggests that many of the cause is most likely to be climatic. birds further south are indeed This would be consistent with the familiar with feeders. low visitation rates reported in New Another suggestion made by York, and high rates in Minnesota Pittaway (1989) is that Pine (Pittaway 1989). Grosbeaks may avoid feeders in Southern Ontario and New York Acknowledgements because of the large numbers there Thanks are extended to the of more aggressive species such as (literally) thousands of OBFS and BlueJay ( Cyanocitta cristata) and CBC participants who generated Evening Grosbeak (Coccothraustes the data used in this analysis. Your vesper-tinus). Both these species, efforts are really appreciated. however, were more abundant at ONTARIO BIRDS DECEMBER 1989 91 Author's note about birds at feeders on a much This paper is only one example of larger scale. For further how the Ontario Bird Feeder information on these surveys, or to Survey can be used, and the data take part, contact the author. are available to anyone for analysis. In 1987-88, the survey was Literature cited expanded continent-wide under Dunn, E.H. 1986. Feeder counts and win ter the name Project FeederWatch. bird population trends. American Birds 40:61-66. Over 7,500 now report from all Pittawo:y, R 1989. Pine Grosbeaks using bird parts of North America, and the feeders. Ontario Birds 7:6'fr67. data allow us to examine questions Bird Observations on Fighting Island, Detroit River, Spring 1988 by Martin K. McNicholl Introduction published for other parts ofEssex Fighting Island lies in the Detroit County except in brief notes and in River, south ofWindsor, Essex wider regional works by A.H.