Rory P. Wilson

Recording Devices on Free‐Ranging Marine Animals: Does Measurement Affect Foraging Performance?

Observations of foraging patterns are essential to understanding the energetic ecology of marine animals. However, direct observations are not often feasible in the field because most foraging takes place below the sea surface or at great distances from land. Attachment of data-recording devices to animals can greatly facilitate the collecton of meaningful data. Devices are being used to an increasing extent on marine mammals (Kooyman et al. 1976, Ray et al. 1978), birds (Kooyman et al. 1971, 1982, Adams and Brown 1983, Lishman and Croxall 1983, Wilson and Bain 1984a, b), reptiles (Stoneburner 1982), and fish (Voegeli and Piucock 1980, Priede 1983a). These devices may supply data upon recovery (e.g., Kooyman et al. 1971, 1982) or through telemetry to local receivers (e.g., Voegeli and Piucock 1980, Priede 1983a, b) or to orbiting satellites (Stoneburner 1982). The effects of instrument mass and harness attachment on land animals are considered to have the potential of affecting the outcomes of experiments and observations (Dumke and Pils 1973, Gilmeretal. 1974, Perry 1981, Perryetal. 1981). However, the effects of devices on marine animals, which live in a much more viscous medium than air, have not been evaluated. In this study we investigated the effects of attached instruments on the foraging activity of the African Penguin (Spheniscus demersus). We show that instrument size may adversely affect foraging behavior, but that data obtained using devices of varying sizes can be used to back-calculate true foraging parameters of free-swimming penguins without devices. Data-recording devices are especially important in studies of free-swimming penguins because these birds are inconspicuous on the surface of the water and are not visible during their frequent traveling and foraging dives. Instruments have been constructed to record speed (Wilson and Bain 1 984b), foraging range (Wilson and Bain 1984b, Wilson and Achleitner 1985), dive time (Trivelpiece et al., in press), dive frequency and depth (Kooyman et al. 1982, Wilson and Bain 1984a). Results show that African Penguins are capable of sustained speeds of at least 7.5 km/h (Nagy et al. 1984) and that other penguin species forage at depths exceeding 200 m (Kooyman et al. 1982). Measurements of foraging distance have also been used to estimate the energy cost of swimming and to construct energy budgets (Nagy et al. 1984). Devices may affect performance in two ways. The mere presence of a device may modify behavior. However, in our experience with penguins this does not appear to be important; after a short period of adjustment, African Penguins with devices continued their normal nesting activity and entered the sea to forage with frequencies similar to control birds (Wilson and Bain 1984a, b). Second, the mass or drag of a device may retard swimming speed, thus reducing dive depth, foraging range, and the number of prey encountered. Instrument mass in itself probably does not adversely influence foraging behavior because attached devices are usually .05) which suggests that the smallest meters had virtually no effect on foraging behavior. On the other hand, two penguins fitted with an electronic distance meter 14.6% of penguin

Foraging ranges of penguins

Speed/distance meters were deployed on adeliee, gentoo and chinstrap penguins Pygoscelis adeliae, P. papua and P. antarctica , breeding near Anvers Island, Antarctica. Underwater speeds and distances travelled were interspecifically very similar (means of ca. 7–8 km h- 1 and 15–45 km, respectively). These results are compared with published data on penguin behaviour at sea obtained by using identical methodology. A simple model, based on penguin activity at sea data, is developed to derive range limits for penguins. Derived range limits are substantially lower than previous estimates but accord well with distributional data obtained by transects.

Seasonality in diet and breeding success of the Jackass PenguinSpheniscus demersus

Jackass Penguins breed throughout the year but show seasonal preferences. I examined the hypothesis that most birds breed at a time when reproductive potential is most fully realised. By using the numbers of Jackass Penguins returning to the island per 24 hour period as an index of the number of birds breeding, I found that most penguins on the island bred when chick growth was maximal and chick mortality was minimal. The diet of Jackass Penguins was determined by stomach pumping 556 birds. More than 95% of their diet, by weight, consisted of pelagic schooling fish. The local abundance of these fish seemed to determine the breeding success of the Jackass Penguin. Brillenpinguine brüten zwar das ganze Jahr hindurch, zeigen aber jahreszeitliche Präferenzen. Ich prüfte die Hypothese, daß die meisten Vögel zu der Zeit nisten, wenn der höchste Bruterfolg realisiert werden kann. Die Anzahl pro 24-h-Perioden auf die Insel rückkehrender Pinguine wurde als Index für den Brutbestand betrachtet. Tatsächlich brüteten am meisten Vögel dann, als Wachstum maximal und Kükensterblichkeit minimal waren. Die Nahrung wurde durch Magenspülungen bei 556 Individuen ermittelt. Pelagische Schwarmfische machten mehr als 95 Gewichtsprozente aus. Anscheinend bestimmte die lokale Häufigkeit dieser Fische den Bruterfolg.

Conspicuous coloration may enhance prey capture in some piscivores

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Sharing food in the stomachs of seabirds between adults and chicks—A case for delayed gastric emptying

1. Retention times of food in stomachs of breeding and non-breeding African pengiuns (Spheniscus demersus) were examined. 2. Rates of gastric emptying in non-breeding birds were linearly related to the mass of food in the stomach. 3. Breeding birds returned to the nest with more food in their stomachs when chicks were larger. The rate of regurgitation of food was linearly related to chick mass. 4. Retention times of food in the stomachs of breeding penguins can only be explain by cognisance of observed regurgitation rates and by assuming that there is no gastric emptying through the pyloric sphincter.

Contemporary and historical patterns of African penguin Spheniscus demersus: Distribution at sea

Line transects from boats were conducted during 1984 and 1985 to determine African Penguin (Speniscus demersus) distribution in the South African Cape waters. Range limits for breeding birds were derived from information on penguin travelling speeds and durations of foraging trips. Over 50% of all penguins considered to be non-breeding occurred within 20 km of the coast whilst over 50% of all breeding birds occurred within 3 km of the coast. Penguin density decreased with increasing distance offshore. The most frequently encountered penguin group size was one with larger groups decreasing in incidence according to a power curve decay. There was no difference in the frequency of occurrence of different group sizes between breeding and non-breeding penguins, nor did group size distribution change with distance offshore. Data on African Penguin distribution at sea collected in 1984 and 1985 was not discernably different to equivalent data collected between 1954 and 1974. The composition of penguin group size was also the same during both periods.

Spatial and temporal patterns of diet in the Cape Cormorant off Southern African

Diets of Cape Cormorant (Phalacrocorux cupensis) were sampled from 198 1 to 1985, between Mercury (25”43’S) and Dyer (3441’S) islands of the Benguela upwelling ecosystem off Namibia and South Africa. Over 99% of identifiable prey items were pelagic fish: cape anchovy (Engraulis japonicus capensis), 46%; pelagic goby (Suflogobius bibarbatus), 34%; and maasbanker (Truchurus truchurus), 14%. Daily, monthly, and regional variation in diet was three to four times that of annual variation, suggesting that environmental variability in the Benguela ecosystem is greatest at time intervals shorter than 1 year and that caution is necessary when inferring diets of Cape Cormorants from limited sampling.