Short and medium-term variation in the diets of penguins at Marion Island CR Brown Department of Zoology and Entomology, Rhodes University, PO Box 94, Grahams­ town 6140, South Africa NT Klages Port Eliz.abeth Museum, PO Box 13147, Humewood, Port Eliz.abeth 6013, South Africa NJ Adams Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Rondebosch 7700, South Africa Seasonal (within a breeding season) and year-to-year Introduction changes in the diets of the four species ofpenguins breed­ ing at Marion Island are reviewed. King and gentoo pen­ guins, which are resident at the island throughout the Penguins are particularly abundant in the Antarctic ~nd year, show seasonal changes in the relative proportions sub-Antarctic but, until recently, surprisingly little was ofdifferent prey types (fish, cephalopods and crustaceans) known about their diets. However, recognition of their consumed. However, the few available data suggest that importance as predators of marine resources (e g prey species of king penguins vary little from year-to­ Mougin and Prevost, 1980, Croxall and Prince, 1982) has year, whereas those ofgentoo penguins show some var­ stimulated numerous studies on their food and feeding iation. In contrast to king and gentao penguins, macaroni ecologies (see review by Croxall and Lishman, 1987). and rockhopper penguins show marked seasonal and an­ Despite an increase in diet studies, there remain rela­ nual variation in both the relative proportions ofprey type tively few quantitative data spanning full breeding sea­ consumed and the species composition-of their diets. sons and even less spanning more than one season. The Seasonal changes reflect changes in their foraging be­ few available data suggest generally little variation in the haviour during chick-rearing, but year-to-year c,1'anges diets of penguins in Antarctica both during their respec­ are probably related to hydrographic events, which are tive breeding seasons (Croxal and Prince, 1980, Volk­ known to occur in the vicinity of the island and which man et al, 1980, Lishman, 1985) and annually (Trivel­ alter prey species composition and availability. piece et al, 1983, Croxall and Lishman, 1987), although more recent evidence for Adelie penguins (Pygoscelis adeliae) suggests that such changes may occur at some localities (Green and Johnstone, 1988, Puddlecombe and Seisoenale veranderinge _(binne 'n enke/e broeiseisoen) Johnstone, 1988). Four species of penguins, king pen­ en veranderinge van jaar tot jaar in die dieet van die vier guins (Aptenodytes patagonicus), gentoo penguins pikkewynsoorte wat op Marion-eiland broei, word (Pygoscelis papua), macaroni penguins (Eudyptes beskou. Koning- en gentoepikkewyne, W<lt dwarsdeur die chzysolophus) and rockhopper penguins (E. chrysocome) jaar op die eiland bly, toon seisoenale veranderinge in breed at Marion Island in the sub-Antarctic (46°52 die relatiewe proporsies van die verskillende prooispe­ S,37°51 E). In.contrast to the case at most Antarctic and sies, maar min jaar-tot-jaar-veranderinge. Daar is min sub-Antarctic localities, recent studies at Marion Island data oor koningpikkewyne beskikbaar, maar dit dui have demonstrated both seasonal and annual variation in daarop dat die prooitipes wat in hulle dieet voorkom, van diets of the breeding penguins. This paper reviews cur­ jaar tot jaar min verander. Die dat.a suggereer egter dat rent information, both published and unpublished, on the daar wel veranderinge is in die prooitipes wat deur gen­ diets of the four species of penguins at Marion Island toepikkewyne geeet word. Daarteenoor toon macaroni­ with the objective of highlighting and attempting to ex­ en geelkuifpikkewyne duidelike seisoenale en jaarlikse plain these short-term (within a breeding season) and verandering in sowel die relatiewe proporsies van die medium-term (year-to-year) variations. praoitipe geeet, as die spesiesamestelling van hulle diete. Seisoenale veranderinge reflekteer veranderinge in hulle kossoekgedrag wanneer kleintjies grootgemaak word, Data base maar veranderinge van jaar tot jaar hou waarskynlik ver­ band met hidrografiese gebeurtenisse wat wel in die om­ gewing van die eiland voorkom en wat die Information on general composition of the diets (i e rela­ prooispesiesamestelling en -beskikbaarheid verander. tive proportions of each prey type) and prey species con- S. Afr. J. Antarct. Res. , Vol 20 No I, 1990 13 sumed by the four species of penguins at Marion Island affect the composition of the diets of macaroni and rock­ were obtained from a recent series of quantitative diet hopper penguins, but changes in foraging patterns are studies. King and gentoo penguins are resident at the is­ also an important factor. Both species feed exclusively land and were sampled over a period of one year (Adams on crustaceans early in their respective chick-rearing peri­ and Klages, 1987, 1989). This limited quantitative data ods, when they forage relatively close to their colonies. base allows· assessment of short-term changes, but ye,J.r­ However, as the chicks grow the penguins forage farther to-year changes are restricted to comparisons with previ­ afield and their diets include an increasing proportion ous less detailed studies and opportunistic samples (La of pelagic fish and cephalopods (Brown, 1987, Brown Cock et al, 1984, NJ Adams, unpublished data). and Klages, 1987). · Macaroni and rockhopper penguins were sampled over In contrast to the situation at the Prince Edward Is­ two successive summer breeding periods (Brown and lands, most penguins in the Antarctic and sub-Antarctic Klages, 1987) and additional information was obtained show little seasonal variation in diet. However, Pudd­ from less detailed studies (Williams and Laycock, 1981) lecombe and Johnstone (1988) and Green and Johnstone and from opportunistic sampling (FitzPatrick Institute, (1988) have demonstrated changes in diet in Adelie pen­ unpublished data). guins before and after chick hatching at Magnetic Island, East Antarctica. More recently, Hindell (1989a) report­ Results and discussion ed seasonal variations in the relative proportions of cer­ tain prey species of royal penguins at Macquarie Island (54° S), although rockhopper penguins at the same lo­ Short-term changes cality showed little variation (Hindell, 1989b). In general, king penguins fed on fish and cephalopods, whereas gentoo, macaroni and rockhopper penguins fed on crustaceans, fish and cephalopods, although in differ­ Medium-term changes ent proportions and frequently on different species (see below). During years in which intensive sampling took General composition of the diets place, changes in prey composition were· evident in all Intensive sampling from king penguins has been carried four species of penguins over the course of the respec­ out only over a single year (1984/85), but some quan­ tive sampling periods. For example, king penguins, which titative information on relative numbers of fish and have an extended breeding season of 14 months, fed cephalopods is available from 40 samples covering six predominantly on pelagic squid in winter, but consumed months between September 1981 and May 1982 almost exclusively fish in swnmer (Adams and Klages, (NJ Adams, unpublished data). During this period, fish 1987). This may indicate either a greater availability of comprised an average of 21 % (range 3 - 49%) and cephalopods within reach of the pengqins in winter (when cephalopods the balance. This is in marked contrast to the lower ambient light levels may trigger mesopelagic later sampling when fish generally comprised between squid to rise in the water column), a decrease in the avail­ 80 and 95% by numbers of the diet (Adams and Klages, ability of fish at this time, or both. 1987). However, the absence of very small otoliths in the In gentoo penguins, crustaceans tended to predominate early samples and their presence in large numbers in in the diet early in the year, changing to more fish from 1984/85 suggest that early sorting techniques may have about July, when this species begins breeding (Adams been inadequate to recover these, resulting in an underes­ and Klages, 1989). Williams (1981) first described from timate of numbers of fish consumed. Confirmation of changes in guano colour a seasonal change in the diet potential large variations in prey composition of king pen­ of gentoo penguins from crustaceans to fish and suggested guins must therefore await further intensive sampling. that this was in response to the summer influx of large Although there is relatively little information on gen­ numbers of macaroni and rockhopper penguins which too penguins, samples collected over a full year, March potentially competed for available :cesources, especially to March inclusive, nevertheless still demonstrate differ­ crustaceans. However, Adams and Klages (1989) have ences in general composition of their diets. Thus, in subsequently demonstrated that the change in diet oc­ March 1984, the overall diet comprised 82 % crustaceans curs several months before the arrival of macaroni and and the balance fish, whereas in March 1985 crustaceans rockhopper penguins. Seasonal changes in the diets of were absent, the diet consisting of 85 % fish and 15 % gentoo penguins are, as in king penguins, thus thought cephalopods (Adams and Klages, 1989). Similarly, the to reflect changes in prey availability rather than changes diet of gentoo penguins in September 1982 differed in prey selection. However, in contrast to king penguins, markedly