Nutrient Reserves and Reproductive Performance of Female Lesser Snow Geese

--We studied the relation between nutrient reserves and reproductive performance of female Lesser Snow Geese (Chen caerulescens caerulescens) in 1971 and 1972 at the McConnell River (60ø50'N, 94ø25'W), Northwest Territories, Canada. We determined the potential clutch size of a pre-laying female by counting large (>20 mm), highly vascularized ovarian follicles; actual clutch size of post-laying females was the number of post-ovulatory follicles. Females with larger nutrient reserves had, on average, larger potential clutches. Reserves were used by the geese during laying and, after laying, the mean weights of reserves from females that laid different size clutches were not significantly different. We suggest that clutch size in Lesser Snow Geese is determined by size of nutrient reserves. Successful females used much of their remaining fat and protein reserves during incubation but this use was not significantly modified by the size of clutch they incubated. Late in incubation some females depleted their reserves and left their nests to feed; others starved to death. Thus, to reproduce successfully a female must retain, after egglaying, sufficient nutrient reserves for her own maintenance during incubation. Received 16 May 1977, accepted 14 October 1977. ARCTIC nesting geese feed little during egg-laying and incubation (Ryder 1970, Ankney 1977a). Ryder (1970) hypothesized that clutch size in these species evolved in relation to: (1) the energy reserves that the female accumulates before arriving on the breeding grounds, (2) egg size, and (3) the energy required to complete incubation. Harvey (1971) proposed that depletion of energy reserves was the major cause of nest desertion by female Lesser Snow Geese (Chen caerulescens caerulescens). As field data to test these ideas were lacking we investigated the importance of nutrient reserves to Lesser Snow Geese (both blue and white color phases). Most previous studies of body reserves in breeding birds considered only fat (e.g. Breitenbach and Meyer 1959, Barry 1962, Harris 1970, Krapu 1974). However, we measured protein and calcium reserves in addition to fat (hereafter called nutrient reserves) because: (1) these are the major nutrients in an avian egg (Romanoff and Romanoff 1949), and (2) a fasting goose must metabolize body protein concurrently with fat (Benedict and Lee 1937, Hanson 1962). In this paper we discuss the relationship between the size of a female's reserves, her clutch size, and her ability to successfully complete incubation. METHODS AND DEFINITIONS TWO summers (1971 and 1972) were spent at the nesting colony at the mouth of the McConnell River (60ø50'N, 94ø25'W), Northwest Territories, Canada. Macinnes (1962) has described the area. Females were collected from arrival on the breeding grounds to the start of the wing molt. The breeding phenology and timing of the collection periods were nearly identical in the 2 yr (Table 1). Birds were assigned to the following categories (Ankney 1974, 1977a, has described the collection methods and criteria for assigning birds to categories): Arriving.--Females arriving on the breeding grounds. Laying.--Females that had just completed laying. Some had an oviducal egg and no large follicles; the oviducal egg-weight was subtracted from the body weight. 459 The Auk 95: 459-471. July 1978 460 ANKNEY AND MACINNES TABLE 1. Breeding phenology and collection periods [Auk, Vol. 95