Higher Predators – Signy Island – Penguin monitoring
Three species of penguin breed on Signy Island: Adélie penguins (Pygoscelis adeliae), chinstrap penguins (Pygoscelis antarcticus) and gentoo penguins (Pygoscelis papua). These species have contrasting breeding and foraging strategies and range over different oceanic domains.
Gentoo penguins are inshore foragers that return to shore each night throughout the year, and so are indicators of local food availability in the shelf waters around the South Orkney Islands.
Adélie and chinstrap penguins are much more pelagic, migrating away from their breeding site during the winter, and during the long incubation periods and pre-moult foraging trips when they may range hundreds of kilometres from their colonies. Adélie and chinstrap penguins are therefore indicators of food availability over a much wider area and across a range of habitats; chinstraps tend to be birds of more open water, whilst Adélie penguins prefer to forage in pack-ice. As both species forage further afield they are potentially more able to buffer themselves against localised changes in prey abundance.
Many of the parameters monitored for these penguin species are less variable for Adélie and chinstrap penguins than for gentoos.
In recent years, as seasonal sea-ice extent and duration have reduced across the Antarctic Peninsula and around the South Orkney Islands the three species of penguins have shown differing population responses. Initially, Adélies were declining whilst chinstraps and gentoos were increasing in population. However, as environmental and foraging conditions have changed, the latter two species are now also showing population declines.
Adult arrival weights and laying phenology
Signy Island is a summer only station and in most years it is not possible for scientists to arrive sufficiently early in the season for them to gain information about Adélie penguin arrival weights. However, since 1996, around 50 chinstrap penguins of each sex have been captured and weighed during the period of arrival back on the colony during early November, though the exact date varies between years. Males are generally slightly heavier than females (average of 4.6 vs. 4.5 kg). Arrival weight varies between years. This is probably due to variation in availability of krill during the late-winter and early-spring period, and may influence subsequent breeding population size and performance.
The laying phenology of all three species varies, probably as a result of the prevailing environmental conditions and general foraging conditions. Adélie penguins generally lay their eggs before the start of the field season at Signy Island. The date the first eggs are laid can however be estimated from the hatching dates. The laying date of the first and second egg is usually in November though the first can be laid as early as late October and the second as late as early December. Chinstrap penguins lay their eggs a little later, the first egg is laid in November and the second in early December.
Chick fledging weights
The weights of approximately 100 chicks have been collected just prior to fledging for both Adélie and chinstrap penguins since 1997. The weights of the two species fluctuate between years, suggesting that local food availability has similar effects on chick condition of both species.
Breeding pairs and productivity
The number of breeding pairs of Adélie Loading.. chinstrap Loading.. and gentoo Loading.. penguins have been quantified by undertaking counts at long-term monitoring colonies on the island since 1996. Whole island counts of breeding adults have also been undertaken on an approximately near-decadal frequency.
|Chinstrap Penguin Arrival Mass at Signy||Penguin Egg Laying Phenology at Signy|
|Penguin Fledging Mass at Signy||Total Penguin Population Count at Signy|
|Penguin Population Count in Study Colonies, Signy|