Differences in foraging strategy and maternal behaviour between two sympatric fur seal species at the Crozet Islands

Marine top-predators such as marine mammals forage in a heterogeneous environment according to their energetic requirements and to the variation in environmental characteristics. In this study, the behaviour of breeding females in 2 sympatric fur seal species, Antarctic fur seal Arctocephalus gazella and Subantarctic fur seal A. tropicalis, was investigated in relation to foraging effort. Foraging effort was hypothesised to be greater in Antarctic fur seal than in Subantarctic fur seal due to their shorter lactation period. Using satellite telemetry, time-depth recorders and satellite images of sea-surface temperature and chlorophyll a concentration, the foraging grounds, the at-sea activity budgets and the environmental features were determined for both species breeding on the Crozet Archipelago. Foraging cycle duration was similar for the 2 species, and the seals exhibited similar at-sea activity budgets. Only the proportion of time spent at sea was higher in Antarctic fur seals. Separate foraging areas were identified for the 2 species. Antarctic fur seal distribution was related to bathymetric features, while we did not find any direct relationship between chlorophyll a concentration and seal foraging areas. Our results suggest that Antarctic fur seals tend to respond to the higher needs of their pups by having a higher foraging efficiency and concentrating their foraging activity in the most productive areas.

Where exactly do ground-foraging woodland birds forage? Foraging sites and microhabitat selection in temperate woodlands of southern Australia

Bird assemblages in woodlands of southern Australia are characterised by a high proportion of ground-foraging species, many of which are experiencing population declines. We examined the foraging sites of 13 species of ground-foraging birds, including four common species and nine declining species, in four study areas representing different woodland types. Microhabitat features were recorded within a 3-m radius of observed foraging points and compared with random points. Significant differences between foraging and random plots were detected for all but one species, clearly indicating selection for foraging habitat. However, levels of dissimilarity between foraging and random plots were low, suggesting that much of the woodland study area is suitable for foraging. Microhabitat features of particular importance for multiple species were a low density of trees and shrubs, a high cover of native herbs, and fallen timber on the ground. Sites amidst dense trees tended not to be used. Several species had more particular requirements, such as the Diamond Firetail (Stagonopleura guttata) for grass cover and the White-winged Chough (Corcorax melanorhamphos) for litter cover. There was no evidence that declining species showed a greater degree of selection or were more restricted in the availability of foraging microhabitats than common species. Several of the key attributes of preferred foraging sites, such as tree density, can be actively managed at the local scale. A heterogeneous ground layer is needed to provide suitable foraging habitat for the full suite of ground-foraging birds. Achieving suitable heterogeneity in present-day woodlands will require careful and active management of various disturbance processes.

Above- and below-ground vertebrate herbivory may each favour a different subordinate species in an aquatic plant community

At least two distinct trade-offs are thought to facilitate higher diversity in productive plant communities under herbivory. Higher investment in defence and enhanced colonization potential may both correlate with decreased competitive ability in plants. Herbivory may thus promote coexistence of plant species exhibiting divergent life history strategies. How different seasonally tied herbivore assemblages simultaneously affect plant community composition and diversity is, however, largely unknown. Two contrasting types of herbivory can be distinguished in the aquatic vegetation of the shallow lake Lauwersmeer. In summer, predominantly above-ground tissues are eaten, whereas in winter, waterfowl forage on below-ground plant propagules. In a 4-year exclosure study we experimentally separated above-ground herbivory by waterfowl and large fish in summer from below-ground herbivory by Bewick’s swans in winter. We measured the individual and combined effects of both herbivory periods on the composition of the three-species aquatic plant community. Herbivory effect sizes varied considerably from year to year. In 2 years herbivore exclusion in summer reinforced dominance of Potamogeton pectinatus with a concomitant decrease in Potamogeton pusillus, whereas no strong, unequivocal effect was observed in the other 2 years. Winter exclusion, on the other hand, had a negative effect on Zannichellia palustris, but the effect size differed considerably between years. We suggest that the colonization ability of Z. palustris may have enabled this species to be more abundant after reduction of P. pectinatus tuber densities by swans. Evenness decreased due to herbivore exclusion in summer. We conclude that seasonally tied above- and below-ground herbivory may each stimulate different components of a macrophyte community as they each favoured a different subordinate plant species.