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A very interesting feature of the report was the number of species that must have overslept, or failed to heed the migration urge! Who would expect to encounter, just before Christmas, such birds as: Pintail Duck, Myrtle Warbler, White-throated Sparrow, Song Sparrow or American‘ Goldfinch?

Bruce McLaren

EVENING GROSBEAK BEHAVIOR AT FEEDERS

At the last meeting of the Natural History Soceity, a brief disucssion on Evening Grosbeaks at feeders was brought up. It was noted that there existed an unequal sex ratio and a few ideas were brought up on what factors caused this phenomenon. Coincidentally, one day later, the Autumn 1976 issue of Bird Banding, a journal published by the North- eastern Bird Banding Association arrived. While thumbing through it, I noticed an article entitled "Some factors influencing observed sex

ratios in a population of Evening Grosbeaks" by M.H. Balph and D.F. Balph.

The authors studied grosbeaks in Logan, Utah, during late winter and spring of 1976. Most of their data, however, dealt with the period between mid-April to mid-May. Observations of sex-ratios were made in four situations: (a) crowns of vegetation, (b) during trapping and banding operations, (c) at a large elevated tray, and (d) a small elevated tray (both trays were provisioned with sunflower seeds). The number of grosbeaks present in the area during the study period was estimated to be between 700 and 800 birds.

The sex ratio of females to males at different observation spots varied. Females predominated at the first three situations listed a— bove and males predominated at the small food trays.

The authors suggest several factors which could influence the sex ratios observed within the 200 square meter study area. Differential mortality as a result of conspicuousness of males could account for a higher number of females. This, however, could be countered by dif- ferential mortality as a result of social status (i.e., females, being subordinate in this species, may be at a disadvantage if food resources were limited). Differential migration patterns were also suggested

as a reason for unequal sex ratios and banding records suggested that females may winter further south than males.

The marked difference in the ratio of birds around the small feeding tray was attributed to grosbeaks social behavior. Males readily attacked females and forced them away from the feeding station. Hence, as the size of the feeding station decreases, there is a greater pro- bability of having more males than females in the area because aggres— sive tendencies of the males would increase at a limited food source.

It was interesting to note that many of the factors mentioned in the article were considered or implied during the brief discussion at the annual meeting. The above reference is in Volume 47 of Bird Banding pages 340-344. I'll bring a copy to the next meeting for anyone who would like to find out more about factors influencing grosbeaks at feeders.

Earle Hickey Jr. 231 Grafton Street Charlottetown, P.E.I.