Foraging modes of chinstrap penguins:contrasts between day and night

Abstract

Penguins rely on vision to travel and hunt at sea. Vision in marine predators, particularly those hunting phototactic prey under a broad range of light intensities, must be better understood to realize how these species respond to changes in their environment. We studied the effects of daily cycles in light intensity on visual predators by examining the duration and timing of chinstrap penguins' PjrgosceUs antarctica foraging trips and the size, composition, and timing of their meals. We used radio telemetry and stomach-contents sampling to study adult penguins that were provisioning chicks during the summers of 1993 and 1994 at Seal Island, Antarctica. The penguins rarely initiated or terminated foraging trips at night, but otherwise varied the timing and duration of trips to sea. Cluster analyses using departure and arrival times revealed 5 distinct modes of foraging: 3 were strictly diurnal (early, mid-, and late) and 2 were partly nocturnal (overnight and extended). Durations of diurnal trips (4 to 11 h) were shorter than overnight (13 to 14 h) and extended trips (18 to 22 h). Early and rniddiurnal trips and extended trips were significantly shorter in 1993 than in 1994; late diurnal and overnight trip durations did not differ between years. Diurnal foraging was most common in 1993, whereas overnight foraging predominated in 1994. Shortened diurnal foraging in 1993 appears to have increased the frequency of diurnal foraging by allowing more parent birds to alternate diurnal trips within a single day and by reducing the incidence of birds extending diurnal foraging through the night. That penguins foraged more frequently by day when permitted by shorter trip durations (in 1993) suggests that they opted to forage diurnally whenever possible. Returning dlurnal and overnight foragers had greater than 99 and 74 % Antarctic krill Euphausia superba by weight in their stomachs, respectively However, overnight foragers also returned with significant amounts of highly digested remains of pelagic fish, suggesting birds were in offshore waters talung fish during the night. In contrast, only 1 out of 40 diurnal foragers from both years combined had evidence of fish. Thus, the daily light cycle affected both the timing and duration of chinstrap penguin foraging as well as the type of prey consumed during trips to sea.

Variability in krill biomass links harvesting and climate warming to penguin population changes in Antarctica

“…Rather, sea ice is one of several factors that mediate prey availability to penguins. Antarctic krill (Euphausia superba) is the dominant prey of nearly all vertebrates in this region, including Adélie and chinstrap penguins (6,(11)(12)(13)(14)(15)(16)(17). Large-scale changes in krill biomass best explain why populations of Adélie and chinstrap penguins increased as a result of competitive release following the harvesting of the whales and seals (the krill-surplus hypothesis) (18,19) and why more recently they have decreased as a result of climate change and the recovery of pinnipeds and baleen whale populations (7-10).…”

Long days, long trips: foraging ecology of female rockhopper penguins Eudyptes chrysocome chrysocome at Tierra del Fuego

“…It is known that penguins are visual predators that depend on ambient light to locate prey (Wilson et al 1989(Wilson et al , 1993, that they dive shallower at night than during the day, and that even when successful in catching prey, their foraging success at night is reduced (Wilson et al 1993, Jansen et al 1998). The performance of overnight foraging trips and dives has been recorded in several penguin species.…”

“…Another explanation could be that some filholi females actually stayed on land during night and that this was undetected by the depth readings of the TDRs (in our study, the light-channel readings of our TDRs helped us to distinguish between periods on land and at sea). Finally, another explanation could be a strong device effect on the birds equipped at Macquarie Island that induced very long foraging trips.It is known that penguins are visual predators that depend on ambient light to locate prey (Wilson et al 1989(Wilson et al , 1993, that they dive shallower at night than during the day, and that even when successful in catching prey, their foraging success at night is reduced (Wilson et al 1993, Jansen et al 1998. The performance of overnight foraging trips and dives has been recorded (Chappell et al 1993).…”

Foraging behaviour and reproductive success in Magellanic penguins ( Spheniscus magellanicus ): a comparative study of two colonies in southern Chile

“…9 (cf. Jansen et al 1998). Short foraging trips like the ones at Otway are only possible, when prey availability near the breeding grounds is suciently high and travel distances therefore small.…”

“…Another factor important to mention in this context is the synchronization of the mates (cf. Jansen et al 1998), especially during the guard phase, i.e. the ®rst 4 weeks after chick hatching.…”