The influence of subcolony-scale nesting habitat on the reproductive success of Adélie penguins

Abstract

Group-size variation is common in colonially breeding species, including seabirds, whose breeding colonies can vary in size by several orders of magnitude. Seabirds are some of the most threatened marine taxa and understanding the drivers of colony size variation is more important than ever. Reproductive success is an important demographic parameter that can impact colony size, and it varies in association with a number of factors, including nesting habitat quality. Within colonies, seabirds often aggregate into distinct groups or subcolonies that may vary in quality. We used data from two colonies of Adélie penguins 73 km apart on Ross Island, Antarctica, one large and one small to investigate (1) How subcolony habitat characteristics influence reproductive success and (2) How these relationships differ at a small (Cape Royds) and large (Cape Crozier) colony with different terrain characteristics. Subcolonies were characterized using terrain attributes (elevation, slope aspect, slope steepness, wind shelter, flow accumulation), as well group characteristics (area/size, perimeter-to-area ratio, and proximity to nest predators). Reproductive success was higher and less variable at the larger colony while subcolony characteristics explained more of the variance in reproductive success at the small colony. The most important variable influencing subcolony quality at both colonies was perimeter-to-area ratio, likely reflecting the importance of nest predation by south polar skuas along subcolony edges. The small colony contained a higher proportion of edge nests thus higher potential impact from skua nest predation. Stochastic environmental events may facilitate smaller colonies becoming “trapped” by nest predation: a rapid decline in the number of breeding individuals may increase the proportion of edge nests, leading to higher relative nest predation and hindering population recovery. Several terrain covariates were retained in the final models but which variables, the shapes of the relationships, and importance varied between colonies.

Breeding Ecology of Adélie Penguins in Mid Victoria Land, Ross Sea Antarctica

“…In any case, the effect of nest position on breeding output may thus propagate at a larger scale, influencing the breeding success at the subcolony scale. Subcolonies with a high perimeter-to-area ratio should show lower breeding success due to a higher proportion of peripheral nests [34,48].…”

“…In the same groups, the total number of chicks per nest was counted in mid-January, when usually 2/3 of chicks have entered the crèche stage. A naïve estimation of breeding success at each colony was calculated as the number of chicks counted divided by the number of nests with eggs [32,34].…”

“…It has been shown that breeding skua pairs can travel 50-80 m from their nests into a penguin colony while looking for eggs and chicks [49]; moreover, the median size of skua feeding territory is about 1.1 ha [50], which would correspond to circular territories of about a 60 m radius. Accordingly, Schmidt et al [34] considered the presence of skua nests within 50 m of the penguin colony edge to investigate the effect of skua predation pressure on penguin breeding success. Earlier research conducted at EdPo has also shown that skua pairs nesting within 50 m from penguin nests, especially skuas nesting within 15 m, have a higher fledging success [51], suggesting that distances closer than 50 m from penguin nests can facilitate predation on penguins by skuas.…”

“…Although the effects of environmental factors such as sea ice extent/concentration and sea temperature on breeding output have been largely investigated for strictly Antarctic seabirds [30,31], the effects of the terrestrial environment have been under-studied. Factors related to the quality of the nesting habitat, especially the proximity and number of terrestrial predators, the location of the nesting environment and weather conditions experienced at the nest have been often overlooked, with a few exceptions [32][33][34]. Yet, predator-prey relationships and harsh weather can strongly influence breeding output and population dynamics as much as other factors like food availability [35][36][37][38].…”

“…Intraspecific competition over food resources may have cascading effects on foraging strategies, diet, and breeding performance of penguins [37], and the presence of the Terra Nova Bay polynya may play an important role in facilitating access to foraging areas, reducing the energy-time budget for breeders throughout the reproductive season [25,39]. Breeding success, in the long-term, contributes to colony size [42] and the quality of the terrestrial habitat can thus be an important driver of population growth [34]. The aims of our study were: (1) to report the breeding output of the Adélie penguin in three neighboring colonies inhabited by the metapopulation of Mid Victoria Land; (2) to identify factors of the terrestrial environment possibly affecting hatching and breeding success in this seabird by focusing on two colonies monitored regularly at the fine scale and (3) to provide scientific information on an indicator species, i.e., the Adélie penguin, for the Ross Sea MPA research and management plan [16].…”