No abstract

European starlings add fresh green plants to their dry nest material. Male starlings of our 60-nest-box colony carried 68 different plant species into their nests. Some males were polygynous and had 3-6 clutches, others were monogynous and had 1-2 clutches per reproductive season. The 'nest protection hypothesis' proposes that insecticidal compounds in green plants reduce the parasite load of the nests. The 'courtship hypothesis' predicts that carrying nest greenery is a courtship activity to attract females. The aim of this study was to collect field data suitable for distinguishing these two hypotheses. 1. Some plant species occurred more often in the nest-boxes than expected from their frequency in the nest-box environment. A significant number of these preferred plants were rich in volatiles, some of which are said to be insecticidal. But volatiles could also attract females and/or influence their breeding activity and the chicks' development directly. 2. The males carried greenery into their nest boxes maximal around 5 days before the onset of laying, when pair formation took place, and ceased this behaviour with egg deposition. The total amount of greenery deposited in a nest-box was a function of the number of days of courtship a male needed to attract a female. 3. Polygynous males deposited the same amount of greenery in their first nest as monogynous males. In additional nests polygynous males deposited more greenery. However, this was due to the fact that these additional nests were advertised for a longer time.

Male European starlings (Sturnus vulgaris) intermingle fresh herbs, preferably species rich in volatile compounds, into their dry nest material. In a field study, we investigated whether these herbs affect the mite and bacteria load of the nests and the condition of the nestlings either directly or via parasite control. We examined the amount of herbs and the number of plant species males carried into their nests, the variation of volatile compounds in the headspace air of the nest boxes and mite/bacteria load of the nests throughout the season. The amount of herb material and the number of plant species, the number of substances emanated by these plants and the infestation of the nests with bacteria and mites (Dermanyssus gallinae) increased with season. In a field experiment, we exchanged natural starling nests with experimental nests with or without herbs. We found that the herbs had no effect on the mites but fewer bacteria were sampled in nests with herbs than in nests without herbs. The body mass of the fledging was not related to the season or the mite/bacteria load of the nests. However, nestlings from nests with herbs fledged with higher body mass than nestlings from nests without herbs. Both bacteria and mite load were related to nestling mortality. In nests containing no herbs, the numbers of fledglings declined significantly with the increasing mite load while the mites had no effect on the number of fledglings in nests with herbs. Thus, the nest herbs counteracted the effect of the mites. In conclusion, it seems that volatile herbs can reduce bacterial but not mite infestation of the starling nests. The positive influence of herbs on nestling growth indicates that herbs either directly (perhaps as immunostimulants) improve the condition of the nestlings and help them cope with the harmful effects of mites, or they provide a nest environment beneficial for the nestlings' development by the reduction of germs.

E. 2004. Timing of reproduction in a Darwin's finch: temporal opportunism under spatial constraints. Á/ Oikos 106: 489 Á/ 500.In seasonally unpredictable habitats, organisms cannot anticipate and prepare for a regular yearly reproductive period. Therefore, they opportunistically breed at any time of year. Opportunistically breeding birds are thought to maintain an activated reproductive system all year around. However, always being prepared can be costly and we therefore examined whether an opportunistic breeding strategy is realized in birds that are confined to harsh, climatically unpredictable habitats from which they cannot escape. We studied temporal variations in reproductive activity in small ground finches (Geospiza fuliginosa ) in the Galápagos archipelago, Ecuador, by determining gonad sizes and plasma luteinizing hormone (LH) concentrations. We compared populations from the arid coasts of St. Fé and St. Cruz islands with birds from the St. Cruz humid highlands. The population from the arid St. Fé island increased gonad sizes and LH concentrations at least four months earlier in a wet (El Niñ o) year compared to the following dry year, indicating high temporal flexibility and opportunistic breeding. However, birds had completely regressed gonads for about 10 months between breeding events during a period of drought. Long-term changes in environmental factors such as ambient temperature, daylength and light intensity did not appear to influence reproductive activity. Instead, environmental signals more directly connected to the occurrence of rains such as humidity, barometric pressure, or rainfall itself may stimulate reproduction. Our data demonstrate that small ground finches regulate the onset of reproductive activity flexibly like other opportunistic breeders. However, they differ from those by their unusual long-term quiescence of the reproductive system during dry periods, which might minimize costs. Our findings suggest that within the continuum from seasonal to opportunistic breeding strategies, organisms evolutionarily optimize reproductive strategies to match local ecological conditions.Most habitats worldwide exhibit temporal fluctuations in biotic and abiotic conditions. Since reproduction is energetically expensive, animals living in variable environments breed only when conditions are suitable for the production of viable offspring (Bronson 1989, Wingfield and Kenagy 1991, Wallen and Schneider 1999. In birds, reproduction is particularly closely tied to favorable environmental conditions, because most birds have small body sizes, high metabolic rates and specialized dietary needs for raising their offsping (Dawson et al. 2001). During the non-breeding season, most birds completely shut down their reproductive system and are thereby able to allocate resources to other seasonal activities like molt, migration or overwintering.While the complete inactivation of the reproductive system during the non-breeding season conveys energetic