Eduardo Mínguez

Effects of paternal care on reproductive success in the polygynous spotless starling Sturnus unicolor

Abstract For males of socially polygynous avian species like the spotless starling, there may exist a trade-off between investing in paternal care and controlling several nests. To determine how the intensity of paternal care affects reproductive success per brood sired or expressed as the total number of young raised in all nests controlled by the same male, it is necessary to manipulate paternal care. Testosterone (T) has been shown to depress the tendency for males to care for their young, and induces them to acquire more mates. The effects of paternal care on reproductive success were studied by treating certain male starlings with exogenous T and others with the antiandrogen cyproterone acetate (CA), and comparing the parental behavior of T- and CA-males throughout the breeding season with that of controls. CA-males fed their chicks more during the first week after hatching than T-males, with controls feeding at intermediate rates, both on a per nest basis and as total effort for all nests controlled by the same male. Paternal feeding rates during the first week of chick life had a significant positive effect on the number of fledged young. The hormone treatment significantly affected the number of chicks raised per nest, CA-males having a higher breeding success per nest than T-males, and controls showing intermediate levels of success. There was no significant effect of treatment on total reproductive success attained by males throughout the season. In the polygonous spotless starling, the intensity of paternal care of young affects reproductive success per nest positively but not on a seasonal basis.

Olfactory nest recognition by British storm-petrel chicks

Abstract Precocial or semi-precocial chicks of underground-nesting seabirds are able to explore the immediate confines of the nest site. Therefore, the development of a cognitive ability that allows chicks of colonial seabirds to return to their own nest during the nestling period may be necessary if contact between young and parents is maintained simply by strong nest-site attachment. In Procellariiformes olfaction may play an important role in navigation of adults to colony sites and nesting burrows. A series of experiments with British storm-petrel, Hydrobates pelagicus , nestlings suggested that they also possess an olfactory homing ability and that they are capable of nest recognition a few days after brooding ceases. As there is apparently no parent–offspring recognition in this species, and adults direct care towards any young that stays in its nest, the ability of chicks to recognize their own nests by smell is likely to be selected for.

LIVING CLOSE, DOING DIFFERENTLY: SMALL-SCALE ASYNCHRONY IN DEMOGRAPHY OF TWO SPECIES OF SEABIRDS

Studies on spatiotemporal pattern of population abundance predict that close populations should exhibit a high level of synchrony, reflected in a parallel time variation of at least one demographic parameter. We tested this prediction for two threatened species of Procellariiformes sharing similar life history traits: the European Storm Petrel (Hydrobates pelagicus) and the Balearic Shearwater (Puffinus mauretanicus). Within each species, we compared adult survival, proportion of transients (breeders that do not settle), and average productivity at two neighboring colonies. Physical and environmental features (e.g., food availability) of the breeding sites were similar. However, while Balearic Shearwater colonies were free of predators, aerial predators occurred especially in one colony of the European Storm Petrel. Despite this difference, we found similar results for the two species. A high proportion of transient birds was detected in only one colony of each species, ranging between 0.00-0.38 and 0.10-0.63 for the petrels and shearwaters, respectively. This seems to be an emergent feature of spatially structured populations of seabirds, unrelated to colony size or predator pressure, that can have important demographic consequences for local population dynamics and their synchrony. Local survival of resident birds was different at each colony, an unexpected result, especially for predator-free colonies of Balearic Shearwater. Productivity varied between the two colonies of European Storm Petrels, but not between the two colonies of Balearic Shearwaters. We demonstrated that within each species, several demographic parameters were colony specific and sufficiently different to generate short-term asynchronous dynamics. Our findings suggest that, in spatially structured populations, local factors, such as predation or small-scale habitat features, or population factors, such as individual quality or age structure, can generate unexpected asynchrony between neighboring populations.

Self-odour recognition in European storm-petrel chicks

In common with many other species of Procellariform, the European storm-petrel (Hydrobates pelagicus) has a well-developed olfactory anatomy, and chicks are able to recognize their own nests by smell. However, it is not known which olfactory cues these birds use to locate their burrows. To find out if body scent is one of these olfactory cues we used a T-maze device to perform three different preference tests. Chicks were allowed to choose between their own odour plus their nest, and a neutral odour; between their own odour and a neutral odour (far from any nest); and finally between their own odour and the body scent of a conspecific chick. Storm-petrel chicks can apparently recognize their own body odour, even when tested against the body scent of a conspecific. Individually distinctive odours may play an important role in facilitating nest recognition. The results indicate self-odour recognition, and suggest that individual odour recognition could play an important role in social relationships of storm-petrels.

Factors affecting breeding distribution of Storm-petrels Hydrobates pelagicus in Orkney and Shetland Capsule The main factors are past and present human activities, especially the introduction of rats to islands

Capsule The main factors are past and present human activities, especially the introduction of rats to islands. Aims To assess factors that influence breeding distribution and abundance of Storm-petrel. Methods We used a database for 142 islands in Shetland and Orkney. Breeding status of Storm-petrel was related to data for each island on introduced and indigenous predators, other human-related features, and aspects of island geography. Results Although 92% of the total land area of the archipelagos comprised islands with rats present, Storm-petrel colonies were almost totally restricted to rat-free islands. They also occurred more frequently on islands with cliffs, far from neighbouring islands with humans, and on islands with a low rate of human visits. Colony size was smaller on the smallest occupied islands. Breeding numbers of Great Skuas Stercorarius skua, Great Black-backed Gulls Larus marinus, and Storm-petrels all correlated, as each increased with island size. Conclusions The presence or absence of rats is the single most important influence on Storm-petrel breeding distribution in Orkney and Shetland. However, geographical and human-related effects, such as the presence of cliffs or the occurrence of human visits, also appear to influence the distribution of Storm-petrels, whereas avian predators appear to have had little effect until now.

The Costs of Incubation in the British Storm-Petrel: An Experimental Study in a Single-Egg Layer

The balance between investment in current reproduction and future survival or reproduction may be particularly important to long-lived species. Many of these species are single-egg layers for which incubation costs cannot be realistically measured by manipulation of clutch size. Here I report an experiment in which I manipulated the costs of incubation in the British Storm-petrel Hydrobates pelagicus by prolonging and shortening the incubation period by exchanging eggs between clutches with an average difference in laying dates of 9 days. Hatching success was higher in nests in which the incubation period was shortened than in nests in which it was prolonged. However, neither fledging success nor chick growth differed between treatments. Experimental manipulation of the incubation period affected laying date in the subsequent year. This finding suggests that incubation is costly in Storm-petrels and that the reproductive effort in one breeding attempt may influence reproductive decisions in subsequent breeding attemps in long-lived seabirds.

Is Laying a Large Egg Expensive? Female-Biased Cost of First Reproduction in a Petrel

ABSTRACT. Differential reproductive investment between sexes can lead to asymmetric costs of reproduction in birds. Long-lived procellariiform seabirds are single-egg layers with little sexual dimorphism and similar parental investment in incubation and chick rearing. However, sex-specific tasks exist at the beginning of the breeding season, including egg production by females (no courtship feeding by males in this group of species) and nest and mate guarding by males. Costs of reproduction could be evident during critical periods such as the first breeding attempt, because of inexperience in reproductive tasks or a higher proportion of low-quality individuals in young age classes, or both. Little is known about sex-specific costs of reproduction in monomorphic species, in which we expect costs to be similar. We investigated the effects of first reproduction on the subsequent survival of male and female European Storm-Petrels (Hydrobates pelagicus) and found that female survival (0.72; 95% confidence interval [CI]: 0.60–0.82) was lower than that of males (0.85; 95% CI: 0.76–0.89) after first reproduction. However, these differences were not observed in subsequent breeding attempts by experienced females (0.89; 95% CI: 0.86–0.91) and males (0.88; 95% CI: 0.86–0.91), probably because of an experience-related improvement in foraging efficiency, reproductive tasks, or predator avoidance. The effort invested by inexperienced females in the production of a large egg (≤25% of adult body mass) may explain our observed differences in survival.

Fire benefits flower beetles in a Mediterranean ecosystem

Despite the abundance of plants that benefit from fire in Mediterranean ecosystems, little is known about the possible presence of fire-favoured insects (other than bark beetles). For two years we sampled invertebrates after two large wildfires in eastern Spain and demonstrate that two flower beetle species, Protaetia morio and P. oblonga (Cetoniidae), show a pyrophilous behaviour. These beetles were much more numerous after the fires than in unburnt plots around the fire perimeter; in addition, these species tended to increase in number with the distance from the fire perimeter and with fire recurrence, especially P. morio. These results were maintained for the two postfire years sampled. The results for the beetles do not support the hypothesis of postfire colonization, but that local populations survived the fire as eggs or larvae protected in the soil (endogenous persistence). We propose that the increase in population size (compared with unburnt zones) could be driven by the reduction of their predator populations, as vertebrates that feed on these beetles were disfavoured by fire. That is, the results suggest that these flower beetle species benefit from fire because fire disrupts antagonistic interactions with their predators (predation release hypothesis). Given the omnipresence of small mammals, soil insects, and fires, the processes described here are likely to be general but unexplored.

Heat loss and site-dependent fecundity in chinstrap penguins (Pygoscelis antarctica)

We study the effects of heat loss and nest site quality on fecundity in a chinstrap penguin (Pygoscelis antarctica) colony on Deception Island, Antarctica. During the austral summers of 1990–1991, 1993–1994, and 1995–1996, 441 randomly selected nests were analyzed. Penguins breeding in the center of subcolonies hatched significantly earlier and had larger broods and than those nesting near or at the edge of the subcolonies. These differences, however, were significantly affected by interaction between year and nest location, being highly significant in colder years, when peripheral nests produce fewer young. Analysis of the rate of heat loss showed that penguins breeding at the edge of subcolonies lost heat twice as rapidly as those breeding in the interior of the subcolony. In a re-occupation experiment, evacuated center nests were re-occupied almost ten times as rapidly as edge nests. An analysis of mean fecundity in the period 1991–1996 and mean wind chill suggested that most of the variability in fecundity among years was related to differences in the rate of heat loss. Subcolonies tend to be as circular as possible, thereby decreasing the proportion of edge nests as the size of subcolony increases. Our results support the site-dependent fecundity hypothesis.