Relationships between Sex of Gosling and Position in the Laying Sequence, Egg Mass, Hatchling Size, and Fledgling Size

--The s x of Canada Goose (Branta canadensis) goslings was not correlated with the position in the laying sequence, egg mass, or size of goslings at hatching. However, male goslings were larger at fledging than female goslings. This suggests that sex determination in Canada Geese and probably in other Anserinae occurs randomly over the laying sequence and that parental allocation of resources is equal for male and female goslings. Received 19 February 1986, accepted 25 August 1986. SEX of offspring may be of unequal value to the fitness of parents if the sex ratio of the breeding population varies or if the "costs" of producing each sex differs (Maynard Smith 1984). If parents provide more care to one sex or if the female can control the sex ratio of her progeny to increase survival of one sex, parental fitness will increase also. The possibility that a female bird can control the sex of her offspring has been suggested (Ankney 1982, Ryder 1983, Weatherhead 1985). Theoretically, this would be adaptive under specific circumstances (Trivers and Willard 1973, Myers 1978). The sex ratio of offspring varies through the breeding season in Red-winged Blackbirds (Agelaius phoeniceus; Fiala 1981, Blank and Nolan 1983) and Common Grackles (Quiscalus quiscula; Howe 1977), and varies with position in the laying sequence in Snow Geese (Chen caerulescens; Ankney 1982; but see Cooke and Harmsen 1983), Ring-billed Gulls (Larus delawarensis; Ryder 1983), and Red-winged Blackbirds (Fiala 1981, Weatherhead 1985). I report on the relationships between the sex of Canada Goose (Branta canadensis) goslings and four variables: position in the laying sequence, egg mass, hatchling size, and fledgling size. The purpose was to determine whether females controlled the sex of their offspring in relation to the position in the laying sequence and to examine if parental allocation of resources, as determined by egg mass, hatchling size, and fledgling size, was equal in the two sexes. STUDY AREA AND METHODS Data were obtained in 1983 and 1984 at Gleddie Lake near Brooks, Alberta, Canada (50ø35'N, 111ø54'W). From late March to late April, I searched for nests daily in 1983 and every 2 days in 1984. Upon discovery, each egg was marked with a waterproof felt pen with the date. The average time recorded between the laying of two consecutive eggs was 1.55 days (SD = 0.33, n = 140). Nearly all nests had one or two eggs when found, although some had three. The degree of egg stain was used to assess the order of laying when more than one egg was found in a nest (Cooper 1978). The sequential position of subsequent eggs in the clutch was determined by additional visits daily or every 2 days during the laying period. Nests with more than three eggs were excluded from the analysis because the difference in the degree of staining was not evident for the two first eggs of a clutch. Eggs were weighed to the nearest gram with a spring scale of 300-g capacity. Egg maximum length and breadth were measured to the nearest 0.1 mm with Vernier calipers. During pipping, embryos were web-tagged (Alliston 1975). In late June and early July, I conducted banding drives in the area to recapture the 5-8-weekold marked goslings. Each gosling was weighed and the length of its culmen and tarsus recorded. I determined sex by cloacal examination and checked for the presence of a web-tag on each individual recaptured. Six-egg clutches with known laying sequence from a number of reservoirs near Brooks were removed and hatched in an incubator at the Brooks Wildlife Center in 1984. Clutches of six eggs were used because they were the most common on the study area. Each egg was isolated in the incubator to identify each gosling. Within 4 h of hatching, each gosling was web-tagged with a numbered metal tag and weighed to the nearest 0.1 g on a Sartorius balance. Sex of each individual was determined after 24 h in a hatching incubator. The sex of 172 goslings was rechecked near fledging. Only 5 initial determinations were found to be incorrect. Contingency tables were analyzed using G-tests 73 The Auk 104: 73-76. January 1987 74 YvEs LEBLANC [Auk, Vol. 104 TABLE 1. Mean + SD egg mass (g) by sex determined at hatching and laying sequence in 6-egg clutches (n = 44).