Pachyptila Desolata Research Articles

Scent of a nest: discrimination of own-nest odours in Antarctic prions, Pachyptila desolata

Petrels and albatrosses evolved well-developed olfactory anatomical structures comparable to those of mammals. To date it has been demonstrated that petrels are attracted by food-related odours, and that some hypogean species have decreased homing performances if anosmic. The ability to distinguish between familiar and unfamiliar odours had not been demonstrated. Here we show that the Antarctic prion, Pachyptila desolata, is able to distinguish between its own nest and that of a conspecific, relying on olfactory cues only. When tested in a maze, only prions with an intact sense of smell made a choice and recognized their own burrow whereas anosmic birds did not. In the absence of leading odours in the maze prions behaved similarly to anosmic birds. These results suggest the mechanism used in the short-range homing process of this species as an olfactory beaconing and suggest the skill of recognising individually distinctive odours. Evolving an efficient identification system in the dark allowed these hypogean petrels to return to their colony at night and recognise their own burrow without singing. This behaviour protects them from predation by skuas, Catharacta skua lonnbergi, that hunt petrels by vision and hearing.

Amphipod-based food web: Themisto gaudichaudii caught in nets and by seabirds in Kerguelen waters, southern Indian Ocean

Comparing food samples from diving and surface-feeding seabirds breeding in the Golfe du Morbihan at Kerguelen Islands to concurrent net samples caught within the predator foraging range, we evaluated the functional importance of the hyperiid amphipod Themisto gaudichaudii in the subantarctic pelagic ecosystem during the summer months. T. gaudichaudii occurred in high densities (up to 61 individuals m-3) in the water column, being more abundant within islands in the western part of the gulf than at open gulf and shelf stations. The amphipod was a major prey of all seabird species investigated except the South Georgian diving petrel, accounting for 39, 80, 68, 59 and 46% of the total number of prey of blue petrels, thin-billed prions, Antarctic prions, common diving petrels and southern rockhopper penguins, respectively. The length-frequency distribution of T. gaudichaudii was similar between the 2 diving species, which fed on 1 large size class of adult individuals, whereas the 3 surface-feeding seabirds preyed upon 2 size classes but in different proportions. Juveniles and adults T. gaudichaudii were equally important in the diet of blue petrels, whereas juveniles and adults predominated in the food of thin-billed and Antarctic prions, respectively. Comparison of T. gaudichaudii found in nets and food samples together with observations at sea indicated that common diving petrels and southern rockhopper penguins fed in the close vicinity of the colonies in the Golfe du Morbihan, whereas blue petrels, and thin-billed and Antarctic prions mainly preyed upon amphipods outside the sampled area. Our study shows that T. gaudichaudii is an important local component of the macrozooplankton community and the main prey for planktivorous seabirds inhabiting the Kerguelen archipelago. In certain areas of the subantarctic zone, it therefore has a trophic role similar to that of Antarctic krill Euphausia superba further south, in Antarctic waters.

Natural and Experimental Changes in Chick Provisioning in a Long-Lived Seabird, the Antarctic Prion

The ability of Antarctic Prions Pachyptila desolata to regulate their provisioning effort was studied at Kerguelen Islands by comparing two seasons when food availability differed, and by experimental manipulation of foraging costs. Antarctic Prions provision their chick by a two-fold foraging strategy: on average, they alternate a long foraging trip 7-9 days long when they build up body reserves and then feed the chick, with 2 or 3 successive short trips lasting 1 or 2 days when they use previously stored body reserves to forage for provisioning the chick. Although hatching success and fledging success were similar for the two seasons examined, chicks produced in 1996 grew faster and were heavier at the end of the study than in 1995. The difference was due to a higher provisioning rate in 1996 resulting from long trips being 2 days shorter than in 1995, because the Antarctic waters where adults are believed to feed on Antarctic krill during these long trips were 330 km further away in 1995 than in 1996. While returning from long trips, and during short trips, prions mainly feed close to the colonies on the amphipod Themisto gaudichaudii. This prey was less available in 1995, but prions were able to switch to other prey. Cost of foraging was increased experimentally by adding mass to adults. Loaded parents differed from control parents only by increasing the duration of long foraging trips. The results of both the experiment and the study of the natural variation indicate that the ability of Antarctic Prions to increase provisioning is limited. Birds kept their body mass stable, provided food loads of similar mass and had short foraging trips of similar duration. During long trips they spent longer time foraging either to reach more distant feeding grounds or to cover higher foraging costs. The main constraint on chick provisioning is probably the necessity for birds to maintain a threshold body mass to limit the risk of increased mortality due to breeding effort; the higher yields during long foraging trips permit them to do so.

Measurement of Chick Provisioning in Antarctic Prions Pachyptila desolata Using an Automated Weighing System

The frequency and mass of meals delivered to ten Antarctic Prion Pachyptila desolata chicks nesting at Bird Island, South Georgia were examined using automated weighing systems, placed in the nest chamber of the burrow. The weighing systems, which consisted of an artificial nest platform mounted on electronic load cells linked to a data logger, recorded the mass of the chick every 10 min. Meal delivery was concentrated in the first few hours after dark with a peak (45% of meals) in the second hour of darkness. The mean number of meals per night per chick ranged from 0.4 to 1.7 with 80% of chicks receiving at least one meal per night; there were no nights when none of the chicks was fed. Chick 9, which had the highest feeding frequency, received smaller meals (mean 18 g) than all of the other chicks (mean 37 g). The mass of first and second meals delivered in the same night was not different nor was there a relationship between meal mass and feeding frequency (except for chick 9). There was no relationship between meal mass and chick age between 5 and 50 days. Meals delivered following a night when a chick received no meal were larger than when a chick had been fed the previous night. The proportion of chicks receiving 0, 1 and 2 meals per night differed from the predicted binomial distribution, assuming the independence of feeding by both parents, with more chicks receiving one meal per night than expected. Comparison with periodic weighing methods indicates that the latter underestimates meal size and feeding frequency. The variation within the small sample of chicks studied indicates the need for large sample sizes to estimate population provisioning parameters. However, the weighing system was very successful in providing accurate data on chick provisioning and, with additional development, could provide data on the individual provisioning strategies of adult birds.

Dietary segregation of krill‐eating South Georgia seabirds

The diets of six of the main seabird species (two petrels, two albatrosses, two penguins) breeding at Bird Island, South Georgia were studied simultaneously during the chick‐rearing period in 1986. For five species, Antarctic krill Euphausia superba was the main food (39–98% by mass); grey‐headed albatrosses took mainly the ommastrephid squid Martialia hyadesi (71%) and only 16% krill. The size of the krill taken was similar between seabird species, although there were small but significant differences between penguins and the other species. Sex and reproductive status of krill, however, was different between all seabird species, reflecting some combination of differences in foraging ranges, selectivity by predators, or differences in escape responses of krill. For the krill‐eating species, the rest of the diet varied substantially between species, comprising Martialia and nototheniid fish (blackbrowed albatross and, along with lanternfish, white‐chinned petrel), lanternfish and amphipods (Antarctic prion and macaroni penguin), and icefish (gentoo penguin). Long‐term data on breeding success and information on diet in 5–10 other years suggest that in 1986 seabird diet and reproductive performance was indicative of a year of good availability of krill around South Georgia. In such circumstances, ecological segregation between krill‐eating species appears to be maintained chiefly by differences in foraging range and feeding methods, which are reviewed. This situation is rather different from the few studies of seabird communities elsewhere, where prey type and size are believed to be the main mechanisms of dietary segregation.

Interannual Variation in the Diet of the Antarctic Prion Pachyptila desolata at South Georgia

SummaryThe diet of the Antarctic Prion Pachyptila desolata was examined using food samples regurgitated by adult birds during five breeding seasons at Bird Island, South Georgia. In all years the diet was mainly crustaceans, with a small proportion of myctophid fish and trace amounts of cephalopods. Antarctic krill Euphausia superba was the dominant prey item in three years and was replaced by calanoid copepods, especially Rhincalanus gigas and Calanoides acutus, in two years of low krill abundance. Differences in the prey species taken and observations of foraging behaviour suggest that in years of low krill availability Antarctic Prions forage closer inshore, taking copepods by filtering surface water through their palatal lamellae. By switching to feeding on copepods Antarctic Prions are apparently able to maintain a comparable level of reproductive success, unlike most other krill feeding species which suffer much reduced reproductive performance in years of reduced krill availability.

Stomach oil and reproductive energetics in Antarctic prions,Pachyptila desolata

We studied energy-provisioning rates and energy requirements of nestlings, as well as energy-expenditure rates of adults in Antarctic prions (Pachyptila desolata) on sub-Antarctic Bird Island, South Georgia. Special emphasis was placed on investigating the role of stomach oil as an energy source for nestlings. Nestlings were periodically weighed overnight (n = 91 nestling-nights, 5 nights), and the mass of food consumed by nestlings was estimated from the sum of positive mass increments recorded over 3-h intervals. Prion nestlings consumed, on average, 36.6 g food per day at the age of peak body mass. The probability of each parent feeding its nestling overnight was 0.57, but feeding frequency varied significantly among nights. The median volume of stomach oil in proventriculi of nestlings was 0.9 mL (n = 44), and was negatively correlated with nestling age. Prion nestlings had a relatively high conversion efficiency of food mass to body mass (0.615), indicating a high energy density of nestling meals. Nestling energy budgets revealed that nestling energy requirements could not be met unless a portion of the food mass delivered by the parents consisted of stomach oil. We conclude that Antarctic prions represent an intermediate position in the spectrum of procellariiform dependency on stomach oil during nestling rearing, with diving petrels (which do not produce stomach oil) at one extreme and storm-petrels at the other. Field metabolic rates of adults feeding nestlings, measured by means of the doubly labeled water technique, averaged 4.16 mL CO2/(g∙h), or 391 kJ/day. We suggest that this relatively low metabolic rate while foraging at sea is important for stomach oil formation, as it permits adults to allocate a greater proportion of energy from ingested food to their young.

Significance of Stomach Oil for Reproduction in Seabirds: An Interspecies Cross-Fostering Experiment

Stomach oil, a complex mixture of neutral dietary lipids, is a unique attribute of seabirds in the order Procellariiformes. With the exception of diving-petrels, all procel- lariiforms produce stomach oil and feed it to their young. We conducted an interspecies cross-fostering experiment on Bird Island, South Georgia, that was designed to reveal how the presence or absence of stomach oil in meals fed to young seabirds influences their growth, development, and survival. Hatchling South Georgia Diving-Petrels (Pelecanoides georgicus), a species that lacks stomach oil, were switched with hatchling Antarctic Prions (Pachyptila desolata), a species that feeds its young stomach oil. Diving-petrel foster parents did not successfully raise prion nestlings, presumably due to the absence of stomach oil in meals fed to nestlings. Prion foster parents successfully raised diving-petrel nestlings to fledging, but growth rates were lower, nestling fat reserves were lower, and fledging was delayed compared with controls. These results suggest that stomach oil is an essential di- etary component for prion nestlings to meet their energy requirements, but diving-petrel nestlings apparently cannot efficiently assimilate stomach oil. This experiment supports the hypothesis that the production of stomach oil is an adaptation that allows breeding seabirds to enhance provisioning rates of energy to the nest, while foraging on a distant and dis-

Interannual variation in the breeding biology of the Antarctic prion Pachyptila desolata at Bird Island, South Georgia

Interannual variation in aspects of the breeding biology of Antarctic prions was studied for three summers (1989–1992) at Bird island, South Georgia. Egg size, mass and incubation period remained constant. Laying, hatching and fledging were significantly delayed and less synchronous in 1991/92 (range of laying dates 51 days compared to 10–15 days in the two other seasons). This was due to an unusually cold and protracted winter, with ice blocking burrows into the spring, restricting availability of nest sites. Brooding lasted longer in 1991/92 but the overall fledging period was unchanged. Skeletal growth rates did not vary amongst years; growth in mass was slower in 1989/90 but fledging mass was similar in all three years. In 1989/90 and 1991/ 92 later hatched chicks grew (in mass) faster. The survival of chicks from hatching to fledging did not vary amongst years or with hatching date. Feeding frequency was similar between years, once allowance had been made for starlit nights. Thus late and asynchronous breeding in 1991/92 did not result in reduced breeding success either through predation or starvation.Crustaceans formed 98–99% of the mass of the identifiable portion of regurgitated food samples. Significant annual variation was found within these crustaceans with the presence of krill (least in 1990/91) being inversely related to that of amphipods and copepods. There was no relationship between diet composition and chick growth or survival. Other seabird species, lacking the morphological specialization for feeding on copepods and amphipods, had very low breeding success in 1990/91, when krill was scarce.

Comparative Population Biology of Four Prions (Genus Pachyptila) from the Indian Ocean and Consequences for Their Taxonomic Status

-We studied the morphometrics, breeding biology, genetics, and calls of Pachyptila desolata, P. salvini, P. belcheri, and P. turtur in the southern Indian Ocean. Multivariate analysis of the measurements of live birds revealed some overlap among closely related taxa. Comparisons of biological data provided evidence for ecological segregation between taxa, based mainly on phenology of breeding but also on diet. Calls differed significantly between taxa, and multivariate analysis showed no overlap between sympatric taxa. These data were then compared with data from other taxa (P. crassirostris and macgillivrayi) and from different localities. We support the recognition at the species level of each of the four study taxa. Received 29 June 1989, accepted 6 November 1989. THE SYSTEMATICS of Procellariiformes, especially at the species level, is unclear (see Bourne 1987). This is partly because related species often overlap in their measurements and color patterns which are the most widely used taxonomic characters in the group. The petrels of the genus Pachyptila, the prions, represent a case in point. Prion taxa have usually been divided into two separate groups: the whale-birds, which comprises desolata, salvini, vittata, and belcheri, and the turtur-crassirostris group (Fleming 1941, Harper 1980). Between 1930 and 1950, the six taxa were grouped in one to three genera and in four to six species (Mathews 1912, 1938; Murphy 1936; Falla 1940; Fleming 1941), with many subspecies (19 listed in Murphy 1936). The situation was clarified by Falla (1940). Harper (1980) concluded, after an extensive study of both live (at sea) and museum specimens, that Falla's six species were valid. However, Cox (1980) recognized only three species: vittata (including desolata and salvini), belcheri, and turtur (including crassirostris). His argument was influenced chiefly by the extreme geographic variation within each species, the very large overlap in diagnostic characters (measurements and coloration), and the possible existence of hybrids (between desolata and belcheri on Kerguelen). One reason for the complexity and contradictions in prion taxonomy may be that most authors have worked on beach-washed and museum specimens (Falla 1940, Cox 1980, Harper 1980). Bill measurements, however, vary widely in relation to age of specimens (shrinkage of up to 18% for bill width; Kin-.ky and Harper 1968), age of birds (Richdale 1944, Serventy et al. 1971, Harper 1980), and sample size. As a consequence, some individuals were misclassified or impossible to assign to a particular taxon (Cox 1980). Thus, it appeared that either differences between taxa should be statistically valid (Fullagar 1972, Harper 1980) or the species ranking would have to be abandoned for some taxa (Cox 1980). Taxonomic problems are now addressed by new methods such as electrophoresis (Avise and Zink 1988, Zink 1988), DNA-DNA hybridization (Sibley and Ahlquist 1981, Sibley et al. 1988), behavior (Jouventin 1982, Bretagnolle in press a), and ecology (Mayr 1970). According to the Biological Species Concept, closely related species occupy different ecological niches (Mayr 1982). Investigation of ecological niches therefore provides a powerful tool for detecting sibling species (Mayr 1970). None of these methods has been used on prions. Consequently, we compared the population biology of four taxa in the Indian Ocean. We studied morphometrics of live adult birds, analyzed their breeding biology (nesting habitats, phenology, diet, and distribution at sea), and measured allozyme variation and calls. The calls are particularly relevant for nocturnal burrowing petrels, because they may act as isolating mechanisms (Brooke 1986, Bretagnolle in press b). We extend our results to the broader literature to attempt a clarification of prion taxonomic status. 305 The Auk 107: 305-316. April 1990 This content downloaded from 207.46.13.101 on Sat, 08 Oct 2016 05:38:24 UTC All use subject to http://about.jstor.org/terms 306 BRETAGNOLLE, ZOTIER, AND JOUVENTIN [Auk, Vol. 107

Assimilation and deposition of wax esters in planktivorous seabirds

AbstractWe have analyzed the lipid composition of meals fed to chicks and determined the ability of chicks to assimilate wax esters in four species of high latitude, plankton‐feeding seabirds: one alcid (Aethia pusilla; Alcidae: Charadriiformes) and three petrels (Pelecanoides urinatrix, P. georgicus, and Pachyptila desolata; Procellariiformes). Up to 63% of the estimated digestible energy in chick meals consists of wax esters. Using 14C‐labeled cetyl palmitate, we have shown that chicks of the four study species efficiently hydrolyze wax esters, with less than 1% of the ingested label excreted in most cases. Labeled fatty acids were assimilated and deposited primarily as triacylglycerols in storage fat depots. The one study species known to store lipids in the proventriculus retained much of the labeled wax ester unhydrolyzed in stomach oils. However, the capacity to store stomach oils was not a requisite for efficient assimilation of wax esters. This study provides the first direct evidence that seabirds have the inherent ability to digest and assimilate wax esters efficiently.

Breeding, Distribution and Status of Barrow-nesting Petrels at Maqaurie Island

A survey of burrow-nesting petrels on Macquarie I. between 1975 and 1982 confirmed breeding of the white-headed petrel Pterodroma lessoni, blue petrel Halobaena caerulea, Antarctic prion Pachyptila desolata, fairy prion Pachyptila turtur, sooty sheanvater Pufinus griseus and common diving petrel Pelecanoides urinatriw. A further six species were recorded. The population size of all burrow-nesting petrels has been adversely modified by alien fauna introduced last century. Of the six species breeding, one is stable, two are diminishing and three are present in very low numbers. Current deterioration of their status is localized and with proper management there may be recovery, particularly of the three last species.

Development of homeothermy in the diving petrels Pelecanoides urinatrix exsul and P. georgicus, and the Antarctic prion Pachyptila desolata

1. 1. Body temperatures of South Georgia diving petrel ( P. georgiens) chicks increased from about 37.5°C at hatching to between 38.5 and 39°C within two weeks. Temperatures of common diving petrel P. u. exsul chicks averaged 38.8°C after two weeks of age. Burrow temperatures varied between 5 and 10°C. 2. 2. Measurements of oxygen consumption and body temperature indicated that chicks achieve effective endothermy at 5°C after 9 days in P. u. exsul, 5–6 days in P. georgicus, and 0 days in the Antarctic prion ( Pachyptila desolata). 3. 3. The maximum mass-specific, cold-induced oxygen consumption of small chicks that we could measure with our apparatus (ca. 5–6 cc O 2/g per hr) was achieved at 5–6 days in P. u. exsul. 3 days in P. georgicus, and 0 days in P. desolata. 4. 4. Mass-specific thermal conductance decreased with age and body size in all 3 species, but was highest in P. u. exsul and lowest in P. desolata. Conductance was similar at the age of effective endothermy in all 3 species (ca. 3 J/g per hr per °C). 5. 5. The period required for the development of endothermy is related to age-specific changes in both conductance and capacity for heat production and it closely parallels the length of the brooding period. 6. 6. It is suggested that the length of the period of thermal dependence of the chick is related to the distance between feeding areas and the nesting site.

The food and feeding ecology of Blue petrel (Halobaena caerulea) and Dove prion (Pachyptila desolata)

The diet of two small burrow dwelling petrels, Dove prion, Pachyptila desolata and Blue petrel Halobaena caerulea, was studied at the subantarctic island of South Georgia by quantitative analysis of 246 food samples regurgitated by adults about to feed chicks. Crustaceans, and particularly krill Euphausia superba, predominate in both species' diet but fish is considerably more important to the Blue petrel. Other dietary differences between the species chiefly involve the relative proportions of krill, copepods (nearly exclusive to Dove prion) and seven amphipod species taken.There is no overlap in the species' chick feeding periods but food differences are likely to reflect prey selection rather than resource availability; differences in prey size are ascribed to use of different feeding techniques particularly relating to bill structure and function. Data on frequency of chick feeding, proportion of oil and presence of pumice in food samples are used to indicate that the Blue petrel feeds further away from the breeding colony than the Dove prion. The significance of the various adaptive differences is discussed.

Ecology of the Feral Cat, Felis Catus (L.), (Carnivora:Felidae) on Macquarie Island.

On Macquarie Island from December 1973 to March 1975 the diet of feral domestic cats (Felis catus) was estimated. There was rabbit (Oryctolagus cuniculus) in 82% of faeces and 71% of guts, rabbits under 600 g bodyweight, about 10 weeks old, were 81% of all rabbits eaten. There were Antarctic prion (Pachyptila desolata) and white-headed petrel (Pterodroma lessonii). Cats ate small numbers of rats, mice and wekas and scavenged on dead elephant seals and penguins, especially in winter. Availability of food in winter seemed to be an important factor limiting the population; adult population was estimated to be 250 to 500 and the area of the island is 120 km2. Prion and white-headed petrel nest in burrows; there was little or no predation by cats on surface nesters such as albatross, giant petrel, southern skua or southern black-backed gull, or on live penguin.