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From August to December, thousands of Black-necked Grebes Podiceps nigricollis concentrate during the flightless moult period in salt ponds in the Odiel Marshes, southern Spain, where they feed on the brine shrimp Artemia parthenogenetica. We predicted that because Black-necked Grebes moulted in a food-rich, predator-free environment, there would be no net loss of body mass caused by the use of fat stored to meet energy needs during remigial feather replacement (as is the case for some other diving waterbirds). However, because the food resource disappears in winter, we predicted that grebes moulting later in the season would put on more body mass prior to moult because of the increasing risk of an Artemia population crash before the moult period is completed. Body mass determinations of thousands of birds captured during 2000-2010 showed that grebes in active wing-moult showed greater mass with date of capture. Early-moulting grebes were significantly lighter at all stages than late-moulting birds. Grebes captured with new feathers post-moult were significantly lighter than those in moult. This is the first study to support the hypothesis that individual waterbirds adopt different strategies in body mass accumulation according to timing of moult: early-season grebes were able to acquire an excess of energy over expenditure and accumulate fat stores while moulting. Delayed moulters acquired greater fat stores in advance of moult to contribute to energy expenditure for feather replacement and retained extra stores later, most likely as a bet hedge against the increasing probability of failing food supply and higher thermoregulatory demands late in the season. An alternative hypothesis, that mass change is affected by a trophically transmitted cestode using brine shrimps as an intermediate host and Black-necked Grebes as final host, was not supported by the data. [ABSTRACT FROM AUTHOR]

We measured deuterium isotope ratios (δ Df) in primary feathers to distinguish first-year from older Pectoral Sandpipers Calidris melanotos captured in Barrow, Alaska, during the breeding season. δ Df showed a distinct bimodal distribution, and model-based clustering placed the δ Df values into two non-overlapping groups. More negative δ Df corresponded to Arctic areas, probably identifying first-year birds with Arctic-grown juvenile feathers retained from the previous year. The more positive values corresponded to lower latitudes, possibly identifying older birds that grew their feathers at non-Arctic latitudes. [ABSTRACT FROM AUTHOR]

Selection pressures due to parasitism play an important role in driving the evolution of life history traits of birds in general and of behaviour at the nest in particular. Eggshell bacterial load has been shown to predict hatching failure (i.e. the probability of embryo infection) but the relationships between the bacterial environment of the nest and life history characteristics of birds remain poorly investigated. We explored interspecific variation in eggshell bacterial load of mesophilic bacteria, Enterococcus spp., Staphylococcus spp. and Enterobacteriaceae groups across 24 bird species and assessed whether bacterial load is associated with breeding traits. Interspecific variation was much higher than intraspecific variation for all measures of bacterial load even after controlling for annual variation. Thus, we were able to assess the correlation between bacterial community characteristics and life history traits. After correcting for phylogenetic effects, we found that nest type, the use of feathers or plants as lining material, and incubation behaviour explained a significant proportion of the variance in bacterial communities on eggshells. The strength of these associations depended on study year, suggesting an important role of environmental conditions for eggshell bacterial load or community. Overall, these results suggest that bacteria on eggshells are associated with bird species traits, probably because birds are mediating the deleterious effect of eggshell microbes through behavioural traits that modify bacterial load. [ABSTRACT FROM AUTHOR]

In many species of birds there is a close relationship between the end of breeding and the start of moult. Late-breeding birds therefore often start to moult late, but then moult more rapidly. This is an adaptive mechanism mediated by decreasing day lengths that allows late-breeding birds to complete moult in time. This study asked how these birds complete moult of the primary feathers more rapidly, and the consequences of this on the mass of primary feathers. Common StarlingsSturnus vulgariswere induced to moult rapidly in one of two ways. In the first experiment, one group was exposed to artificially decreasing photoperiods from the start of moult, whereas the control group remained on a constant long photoperiod. The second experiment was a more realistic simulation. Two groups were allowed to moult in an outdoor aviary. One group started to moult at the normal time. In the other, the start of moult was delayed by 3 weeks with an implant of testosterone. The duration of moult was significantly reduced in both the group experiencing artificially decreasing photoperiods and the group in which the start of moult was delayed. The faster moult rate was achieved by moulting more feathers concurrently. The rate of increase in length of each of the primary feathers, and their final length, did not differ between groups. The rate at which total new primary feather mass was accumulated was greater in more rapidly moulting birds, but this was insufficient to compensate for the greater numbers of feathers being grown concurrently. Consequently, the rate of increase in mass of individual feathers, and the final feather mass, were less in the rapidly moulting birds. A 3-week delay in the start of moult is not an unrealistic scenario. That this caused a measurable decrease in feather mass suggests that late-breeding birds are indeed likely to suffer a real decrease in the quality of plumage grown during the subsequent moult. [ABSTRACT FROM AUTHOR]