Reaction of Lesser Snow Geese Anser caerulescens to early nest failure

Arctic-breeding geese are adapted to short breeding seasons. After loss of a first clutch they do not renest, probably due to time lim­ itation. Thus, all reproductive effort goes into one clutch per year. Furthermore, arctic geese are determinate layers (Cooch 1958), i.e. maximum clutch size is determined by a limited number of developing follicles, and they cannot react to partial clutch loss during laying by producing extra eggs. Several events that are detrimental to a clutch can occur at any time between nest initiation and hatch, such as egg loss, i.e. pre­ dation of single eggs without the parents abandoning the nest, abandonment by the parents of a nest containing one or more in­ tact eggs, and abandonment of the nest after egg predation. Only the last two cases involv­ ing nest abandonment represent nest failure and will be dealt with in the following. Nest failures can occur during incubation or during laying. Whereas failures during in­ cubation always result in a nil reproductive success for the current year as arctic geese do not lay replacement clutches failure dur­ ing laying may not mean total reproductive failure. Nest failure during laying due to abandon­ ment or predation is common. In Lesser Snow Geese Anser caerulescens caerulescens it ranges from 15 to 35% of all initiated nests with an average of 21%; total nest failures during incubation are comparatively infre­ quent and range from 1 to 20% with an aver­ age of 7% (Cooke et al. 1982 and unpublished data). Most pre-incubation nest failures oc­ cur at the one-egg stage (Hamann 1983 and unpublished data). Constraints on egg-laying leave geese with three possible reactions to nest failure during laying (early nest failure, ENF); clutch continuation, parasitic laying, or non-breeding. We expect birds to react to ENF with the strategy that maximizes their fitness after partial clutch loss. Possible costs and benefits of these three options are the following; 1. Clutch continua­ tion, where the female lays remaining eggs in a new nest and incubates them, so salvaging eggs that are left after partial clutch loss; here, birds must acquire a new nest site and invest energy of egg-laying, incubation and brood-rearing just as for a complete clutch. By laying eggs and taking care of them, geese probably ensure the highest possible hatch­ ing success for remaining eggs, but expend energy similar to that necessary for a full clutch. 2. Parasitism, i.e. laying eggs in other females’ nests, may reduce hatching success of remaining eggs (due to poor timing), but saves investment of incubation and broodrearing that may not be profitable when the clutch is reduced. Thus, parasitism could be an alternative salvage strategy after ENF. 3. Non-breeding means that reproductive success for the current year is zero. Arcticnesting geese can resorb developing follicles, thereby reducing their potential clutches; this has been interpreted as reallocation of resources from reproductive tissue to body maintenance to keep a female’s body re­ serves above a critical level (Barry 1962, Ryder 1970, Hamann 1986, Thomas 1988). We do not know to what extent follicular atresia is physiologically possible, i.e. if females can resorb all remaining follicles after first eggs have been laid (and lost). However, we con­ sider this a third option for geese after ENF. The energy drain that laying of a full clutch and raising a brood imposes on a female may jeopardize her survival to the nest breeding season and future reproduction. Raising a re­ duced brood may not be worth the increased risk of not surviving to the nest season; in long-lived species such as geese, reallocation