T. 2004. Seasonal declines in reproductive success of the common tern Sterna hirundo: timing or parental quality? -J. Avian Reproductive success declines over the course of the breeding season in many bird species. Two categories of hypothesis have been evoked to explain this decline. The ''timing'' hypothesis suggests that seasonal declines in breeding success are attributable to the date of laying. The ''parental quality'' hypothesis suggests that seasonal declines result from the fact that young, inexperienced, or low quality birds breed later in the season. To evaluate the relative importance of timing and parental quality, egg exchanges and removals were used to manipulate hatching dates of common terns Sterna hirundo. Indices of quality, attendance, provisioning rates, and reproductive success of birds in three experimental groups (delayed hatch pairs, advanced hatch pairs, and pairs induced to relay) were compared to those of date-matched controls. Pairs that hatched chicks early raised more chicks than pairs hatching chicks late in the season, regardless of initial laying date. This suggests that hatching chicks early is advantageous in itself. Our results, however, also support the parental quality hypothesis. There was a significant negative relationship between natural laying date and fledging success, independent of hatching date. Differences in chick growth and survival suggest that higher quality adults may be able to compensate for the disadvantages of late hatching dates and achieve similar reproductive success to that of pairs hatching chicks early. We found that pairs hatching chicks late in the season were subject to more incidents of kleptoparasitism than those hatching chicks early. This may be a proximate factor contributing to seasonal declines in reproductive success for common terns, although such a mechanism would not be likely in non-colonial species. Failure to control for egg quality may have biased the results of some prior egg exchange experiments. Additionally, altered cost of incubation may be an unavoidable confounding factor in studies designed to manipulate timing of breeding.
Laccase, a multicopper oxidase, catalyses the four electron reduction of oxygen to water. Upon adsorption to an electrode surface, laccase is known to reduce oxygen at overpotentials lower than the best noble metal electrocatalysts usually employed. While the electrocatalytic activity of laccase is well established on carbon electrodes, laccase does not typically adsorb to better defined noble metal surfaces in an orientation that allows for efficient electrocatalysis. In this work, we utilized anthracene-2-methanethiol (AMT) to modify the surface of Au electrodes and examined the electrocatalytic activity of adsorbed laccase. AMT facilitated the adsorption of laccase, and the onset of electrocatalytic oxygen reduction was observed as high as 1.13 VRHE. We observed linear Tafel behavior with a 144 mV/dec slope, consistent with an outer sphere single electron transfer from the electrode to a Cu site in the enzyme as the rate determining step of the oxygen reduction mechanism.
World Breeding Range Double-crested Cormorants are the most widespread of North American cormorants. They are the only species in the United States and Canada regularly found in freshwater habitats. In W a s h i n g t o n , Double-crested Cormorants are found breeding in limited numbers inland (Jewett et al. 1953), but by far the largest numbers breed in marine habitats near and around the San Juan Islands, along the outer coast, and in ~r a~s Harbor.
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