Ian J. Strange’s research while affiliated with Natural Environment Research Council and other places

Predation is a major ecological and evolutionary driver of natural populations, greatly influencing fitness and behaviour of prey species. Small, long-lived petrels are vulnerable to predation at the breeding colonies and are expected to evolve behavioural strategies to minimize predation risks. Using an automatic nest monitoring system and nightly aerial counts, we examined the effect of vegetation cover and moonlight on colony attendance patterns and levels of burrow activity of breeding thin-billed prions, Pachyptila belcheri, on New Island, Falkland Islands. We further investigated how these parameters were related to predation by Falkland skuas. We monitored up to 32 nests in two habitats, one with Tussock grass and one with low vegetation cover. Individuals in both areas were more active at the nest before hatching, and those breeding in the low cover habitat were more active and arrived at the colony earlier, which might reflect an effect of reaction time over predation risk. Nocturnal activity peaks shifted in time as the season progressed, indicating behavioural adjustments to sunrise hours. Moon phase did not affect attendance and activity levels of breeders in either habitat or overall aerial activity, but influenced arrival time at the colony during chick-rearing, individuals arriving later in periods of full moon. Skua capture rates were positively correlated with aerial and nest activity but not with overall breeder attendance and were unaffected by moon phase. Thin-billed prions activity budgets are influenced by environmental parameters that affect their likelihood of being predated. KeywordsPachyptila–Attendance patterns–Predation–Burrow activity–Vegetation cover

Crested penguins (genus Eudyptes) present a unique reversed egg-size dimorphism and hatching asynchrony, with the larger second-laid egg (B-egg) hatching before the smaller first-laid egg (A-egg). Both a higher water vapour conductance and parental favouritism during incubation could explain the shorter incubation period for the B-egg than for the A-egg. Because the incubation period is increased by the presence of a sibling for A-eggs, but not for B-eggs, and because both egg categories have the same incubation period when they are incubated alone, it has been suggested that the difference in incubation period was largely driven by the parental favouritism for B-eggs during incubation. We tested whether A- and B-eggs show a difference in laying density, density at the beginning of incubation and in density decrease during incubation according to the presence of a sibling. Although density at the start of incubation was significantly higher for B-eggs than for A-eggs, the decrease in density during incubation had the same slope for both egg categories. Moreover, the presence of a sibling did not influence densities. We additionally provide two equations that allow the back-dating of laying dates for a clutch of SouthernRockhopper Penguin (Eudyptes c. chrysocome) and we discuss the precision of the method (3.04±2.29days for A-eggs and 2.73±2.10days for B-eggs) for penguins which are increasingly being used as marine environmental sentinels. KeywordsEgg category–Egg measurements–Southern Rockhopper Penguin–Hatching asynchrony–Hatching date–Laying date

Following recent phylogenetic work, Rockhopper Penguins were suggested to consist of two or three species. For the Southern Rockhopper Penguin Eudyptes c. chrysocome, sexual dimorphism has not been studied in detail, and only a few previous studies on penguins have investigated sexual dimorphism in immatures and chicks. Using data in the literature, we examined whether the sexual dimorphism of adults varies among the three taxa of Rockhopper Penguins and then we investigated the most reliable measurements to sex adult Rockhopper Penguins. We observed that bill length is the most useful measurement to separate males from females. To allow for sex discrimination in the field, we also examined a large dataset of Southern Rockhopper Penguins from New Island, Falkland Islands, including adults sexed via observation of behaviour, and immatures and chicks sexed genetically. We found that male adults and immatures were larger than females in bill length and bill depth and, to a lesser degree, in flipper length

Central place foragers are constrained in their foraging distribution by the necessity to return to their nest site at regular intervals. In many petrels that feed on patchily distributed prey from the sea surface over large foraging areas, alternating long and short foraging trips are used to balance the demands of the chick with the requirements of maintaining adult body condition. When the local conditions are favourable for prey density and quality, adults should be able to reduce the number of long foraging trips. We studied the flexibility in foraging trip lengths of a small pelagic petrel, the thin-billed prion Pachyptila belcheri, over three breeding seasons with increasingly favourable, cold-water conditions. During a warm-water influx in February 2006, chicks were fed less frequently and adults carried out foraging trips of up to 8days. When conditions became more favourable with colder water temperatures in 2007 and 2008, thin-billed prions decreased trip lengths, more often attended their chick every day, and long foraging trips of six to eight days were not registered during 2008. Chick growth rates mirrored this, as chicks grew poorly during 2006, intermediate during 2007 and best during 2008. Thin-billed prions preyed mainly on squid during incubation and mainly on amphipods and euphausiids during chick-rearing. In the poorest season only, the diet was substantially supplemented with very small copepods. Together, the present results indicate that during warm-water conditions, thin-billed prions had difficulties in finding sufficient squid, amphipods or euphausiids and were forced to switch to lower trophic level prey, which they had to search for over large ocean areas.

In birds, the period spent brooding or guarding young chicks is highly variable, but such variation has seldom been studied. Previous single-year studies of Antarctic petrels Thalassoica antarctica and grey-headed albatrosses Thalassarche chrysostoma revealed a pronounced seasonal decline in brood-guarding duration and gave rise to the ‘synchronisation hypothesis’, which suggests that some of the variation in the length of the brood-guarding stage is related to predictable seasonal changes in the risk of chick predation. We tested the predictions of this and three other hypotheses in a two-site, four-year study of the black-browed albatross T. melanophris. The existence of a pronounced seasonal decline in brood-guarding duration was apparent at both sites, and in years of contrasting food availability, providing further support for the ‘synchronisation hypothesis’. Alternative explanations for this pattern are that short brood-guarding periods for late-hatched chicks result from a seasonal decline in food availability or from the fact that early nesting birds are of higher individual quality. However, these explanations are at odds with the absence of a seasonal decline in early chick growth or in probability of chick survival. Furthermore, adult quality (measured as past reproductive performance) had a weak and inconsistent effect on the duration of brood-guarding. Weather changes explained some of the variation in brood-guarding, but there were no differences between regions of contrasting climates. Individual pairs displayed a degree of inter-annual consistency in brood-guarding duration and, at least in some years, longer brood-guarding resulted in higher fledging probability. We speculate that a higher investment in brood-guarding increases the cost of reproduction, which counteracts other selective pressures that would otherwise lead to longer brood-guarding durations.

All crested penguins present a unique reversed hatching asynchrony: the larger second-laid egg (B-egg) hatches before the smaller first-laid egg (A-egg). Although both eggs often hatch, the A-chick generally dies of starvation within days after hatching. However, within rockhopper penguins, the population at the Falkland Islands is unique in that some birds manage to raise both chicks. Although it has been suggested that the egg size dimorphism between A- and B-eggs may explain how long both eggs and chicks survive, this hypothesis has never been explicitly tested. We expect that both eggs are retained longer in the less dimorphic clutches than in the more dimorphic ones. In this paper, we have compiled egg measurements for three rockhopper penguin species (Eudyptes chrysocome, E. filholi and E. moseleyi) in order to compare the intra-clutch egg size dimorphism among these species. Furthermore, we have collected new data to compare egg size dimorphism between two populations of E. chrysocome (Falkland Islands versus Staten Island). A-egg volumes are more variable between species and populations than B-egg volumes. E. chrysocome and especially the population from the Falkland Islands produces the largest A-eggs and the least dimorphic eggs. Nevertheless, as differences in A-egg volumes between species and between the populations of Falkland Islands and Staten Island are stronger and more significant than differences in egg dimorphism, we suggest that A-egg volume, more than egg dimorphism, could be one of the factors influencing the prevalence of twins. A large A-egg and/or reduced egg dimorphism is probably necessary to enable rockhopper penguins to raise two chicks, but other reasons may also be involved which enable them to keep both eggs and chicks. KeywordsRockhopper penguin-Egg dimorphism-Geographical variation-Chick survival

The Snares Penguin (Eudyptes robustus) breeds only on the Snares Islands, New Zealand, and is vagrant throughout the New Zealand region and southeast Australia. The only previous record outside this area was one in the Falkland Islands in 1988. We report the unusual occurrence of two Snares Penguins in the same colony in the Falkland Islands in 2008, and discuss identification issues. Vagrant penguins demonstrate the incredible dispersal ability of these flightless birds. Received 9 March 2009. Accepted 19 July 2009.

Seabird colonies provide rare opportunities to study trophic segregation in an entire bird community. We here present data on nitrogen and carbon isotope ratios of eight species of seabirds from New Island, Falkland Islands, and compare trophic levels (TL) and foraging distributions. We included adult feathers representing the interbreeding season, as well as chick feathers or down representing the breeding season. The stable isotope ratios indicated differences in feeding areas and TLs between species, consistent with the data of previous conventional diet analyses and observations at sea. We further reviewed conventional and stable isotope seabird community studies calculating the means and ranges of TLs observed across these studies. The mean TL (3.7) of the seabird community on New Island was at the lower end of the mean value range (3.5–4.5), but not significantly different, from the reviewed seabird communities. Seabirds on New Island had a range of 1.3 TLs, which is on the upper end of ranges within a community (0.4–1.5), indicating strong trophic structuring.