The difference between night and day: The nocturnal and diurnal activity budget of gray seals ( Halichoerus grypus ) during the breeding season

All pinniped species are constrained to give birth and raise their pups on land or ice (Bartholomew 1970). This constraint has allowed for detailed behavioral observations on several species of pinniped during the breeding season (e.g., Redman et al. 2001, Dobson and Jouventin 2003, Maniscalco et al. 2006, Young and Gerber 2008). From these observations, activity budgets (also referred to as time budgets) can be calculated; typically to provide information on how individuals, or groups of individuals, partition their time across defined behavioral categories (e.g., Boness 1984, Anderson and Harwood 1985, Arnold and Trillmich 1985, Trillmich 1986, Lydersen et al. 1994, Twiss and Franklin 2010). However, observational studies are usually constrained to daylight periods and, as a result, there is little information from behavioral observations on any pinniped species during the breeding season (or while hauled out) at nighttime (gray seals, Halichoerus grypus, Anderson 1978; southern elephant seals, Mirounga leonina, Galimberti et al., unpublished data cited in Galimberti et al. 2002). Yet, for some species, such as the gray seal, which breed in temperate regions during autumn and winter, daylight periods can be as little as onethird of the circadian cycle. The paucity of studies investigating nighttime activity budgets of pinnipeds on land (breeding colonies or haul-out sites) has previously been attributed to technological limitations in commercially available night-vision equipment (Shipley and Strecker 1986, Acevedo-Guiti errez and Cendejas-Zarelli 2011). Where recent techno-