Years Of Poor Conditions Research Articles

Shearwaters' nest attendance patterns throughout the lunar cycle: Are oceanographic conditions decisive for timing of nest arrival?

The moon cycle has long been recognized as a driving factor of animals' behavioural patterns. However, its influence on seabirds' nocturnal behaviour remains poorly understood. Using a long-term GPS tracking dataset from Cory's and Cape Verde shearwaters (Calonectris borealis and Calonectris edwardsii, respectively) in the Berlengas, Azores, Madeira and Cape Verde archipelagos, North Atlantic Ocean, we investigated nest attendance patterns of breeding birds in relation to oceanographic and natural light conditions during mid-chick rearing. We intended to understand if inter-annual changes in oceanographic conditions around each colony were related with timing of nest arrival and respective light intensity at burrow entrance. For this, oceanographic conditions were evaluated using proxies for marine productivity and metrics of shearwaters' foraging effort. We also wanted to investigate if birds adjusted nest attendance in relation to moonlight throughout the lunar cycle, and whether these patterns changed with contrasting oceanographic conditions. Shearwaters stayed longer at sea after sunset in years of good oceanographic conditions, returning ashore earlier in years of poor conditions, mostly under twilight. Breeding birds also seemed little influenced by moonlight at colonies, although this did not seem to be the case at sea. In particular, they adjusted nest arrivals with the onset of waning moon nights (nights starting without moon), but delayed nest entrances throughout waxing moon nights (nights entailing a growing period of moonlight until moonset). However, this pattern was not extensible to years of poor foraging conditions, when birds returned ashore regardless of moonlight conditions. Combined, these results show that the nest attendance behaviour is mediated by moonlight in Cory's and Cape Verde shearwaters, a pattern that seems to be regulated by prevailing oceanographic and foraging conditions.

Personality influences foraging of a seabird under contrasting environmental conditions

Personality is relevant in shaping the way animals respond to environmental conditions. Some personality traits may be disadvantageous under non-optimal environmental conditions, reducing foraging success and breeding performance in the long term. In this study we tested whether individual personality plays a role in determining shifts in seabirds' foraging behaviour and habitat use when environmental conditions are poor. We used GPS-tracking information from chick-rearing Cory's Shearwaters (Calonectris borealis) during eight consecutive years. Boldness was measured by the response of the tracked individuals to a novel object presented at their nest. Foraging habitat was identified as the environment within geographic points where birds were flying at low speed with high turning rates. We found that bold individuals displayed more foraging habitat consistency and boldness influenced foraging habitat during years of poor environmental conditions. Bold individuals tended to remain closer to the colony under poor environmental conditions, while shy individuals dispersed considerably farther from the colony. However, there was no influence of the personality on breeding success, and the whole population tended to have a lower probability of breeding success during years of poor conditions. During adverse environmental conditions, shy birds shifted habitat, probably as consequence of exploitative competition with the bold birds, but this has no effect on the birds' ability to successfully raise a chick.

Spatially variable response of native fish assemblages to discharge, predators and habitat characteristics in an arid-land river

Summary 1. Fish assemblages and habitats were sampled annually at fixed sites in three tributaries of the Gila River catchment over a 21-year span that included prolonged low- and high-flow periods. Model selection was used to evaluate responses of seven native fishes with variable ecological traits (four small-bodied cyprinids, one large-bodied cyprinid, and two large-bodied catostomids) to mean annual discharge and predacious non-native fishes across the three sites. We also compared habitat use and overlap of native and non-native fishes to identify potential for negative interactions among species. 2. Assemblage structure (species abundance and richness) and recruitment of native species was strongly and primarily affected by mean annual discharge and secondarily by location and densities of non-native predators (mainly the centrarchid Micropterus dolomieui). 3. Densities of age-0 catostomids and small-bodied cyprinids were positively associated with discharge, and this pattern was strongest in the tributary with the lowest densities of non-native predators. Absence or extreme low abundance of natives during low-flow years was most pronounced at the sites where non-native predators were comparatively common. Densities of adults of large-bodied native species also varied by site, but often were positively associated with densities of non-native predators. 4. Spatially variable responses of native fish assemblages indicated that the persistence of native fishes could be jeopardized if key habitats were lost or flow regimes unnaturally altered, particularly during low-flow conditions when recruitment of native fishes is low and predation by non-natives is high. Large-bodied species may be less vulnerable to multiple years of poor conditions because adults are able to avoid predation by non-natives and thus can rely on occasional high discharge years for successful recruitment. 5. As in other arid-land streams, native fish assemblages of the Gila River Basin continue to decline. Our results indicate that conservation requires specific knowledge and consideration of physical influences as well as life-history attributes of native and non-native fishes.