Manuela G. Forero

CAUSES AND CONSEQUENCES OF TERRITORY CHANGE AND BREEDING DISPERSAL DISTANCE IN THE BLACK KITE

Factors affecting individual variation in between-year territory change and dispersal distance were measured in a long-term study of Black Kites (Milvus migrans) living in an area of ∼100000 ha in and around Donana National Park in southern Spain. Adult birds (N = 210) and fledglings (N = 3061) were individually marked, and breeding birds were monitored annually during 1989–1996 to detect banded individuals. Of these 3271 birds, 652 breeding birds were resighted, and 164 of them were sexed through copulatory behavior. Nests were checked annually to monitor breeding performance. Frequencies of return between years were 83.1% for breeding males and 89.5% for breeding females. Frequencies of territory change were 25.6% and 32.8%, respectively. Females >8 yr old rarely changed territories. Dispersing birds departed significantly more from low-quality territories (evaluated through breeding success variables). Breeding failure and mate loss (divorce or death) favored breeding dispersion, both in males and fema...

CAUSES AND FITNESS CONSEQUENCES OF NATAL DISPERSAL IN A POPULATION OF BLACK KITES

Natal dispersal is of central interest when determining demography and genetic structure of populations and managing endangered species with fragmented distributions. However, methodological limitations linked to spatial and temporal constraints have prevented studies of natal dispersal in long-lived birds. Moreover, the consequences of natal dispersal have mainly been related to the first breeding attempt rather than to lifetime reproductive success. We studied the causes and fitness consequences of natal dispersal in a population of Black Kites at Donana National Park (southern Spain). From 1986 to 1995 we marked 2929 nestlings with plastic numbered bands. We annually monitored marked birds in breeding territories, their breeding success, and the survival of nonbreeding birds. Additionally, we searched for marked birds in broad areas of the Iberian Peninsula and North Africa. Median natal dispersal distance was 4.8 km (N = 285), with males more often dispersing shorter distances and females dispersing at all distance categories equally. Density of conspecifics negatively affected dispersal distances of both males and females. In addition, single and first-hatched males born in areas with high breeding density dispersed shorter distances. Dispersal distances tended to be correlated between siblings, possibly a result of sharing similar environmental conditions. We did not find evidence that dispersal was an active mechanism aimed to prevent close inbreeding. Patterns of dispersal in this population are probably driven by intraspecific competition. Males that dispersed shorter distances showed higher lifetime reproductive success (LRS). LRS did not differ among females dispersing different distances, but females that dispersed farther mated with more experienced males. These sex differences in dispersal patterns and their consequences may be explained by the inequality between sexes in breeding roles in this species. Familiarity with the natal area could be important for males, which defend territories and resources, while females may increase their fitness through mate choice and breeding dispersal. High levels of philopatry in Donana National Park may be a result of a surplus of food resources and the effects of conspecific attraction in densely populated areas. However, the degree of philopatry may vary between populations and with time, subject to differences in ecological pressures.

CONSPECIFIC FOOD COMPETITION EXPLAINS VARIABILITY IN COLONY SIZE: A TEST IN MAGELLANIC PENGUINS

Food availability has been proposed as one of the main factors regulating population sizes in birds. Seabirds have provided evidence for the hypothesis that food depletion due to intraspecific competition explains variability in colony size. However, the predictions derived from this hypothesis have not been fully tested due mainly to the difficulties in measuring food availability in marine environments. We measured stable isotopes of nitrogen (d 15 N) and carbon (d 13 C) in the blood of Magellanic Penguins (Sphen- iscus magellanicus), which reveal information about their consumed prey and foraging habits. We tested if conspecific competition causes food depletion, affecting penguin breed- ing performance and, ultimately, the size of the colonies. Blood d 15 N values of adults and chicks significantly decreased with increasing size of their colonies and with the number of conspecifics breeding within the parental foraging ranges. This suggests that high breed- ing densities provoke the depletion of high-quality prey (mainly anchovy). We also found positive relationships between d 13 C values and density of conspecifics within the parental foraging ranges, indicating that when competition for food is high, individuals tend to feed closer to the colony on prey of lower quality. Adult d 15 N values were positively correlated with breeding success at the colonies, which was negatively correlated with the density of conspecifics within foraging ranges. Moreover, d 15 N values of fledglings were positively correlated with their body condition but not with their T-cell mediated immune response considered as two measures of their survival prospects. This decreased breeding output was translated to the colony-size structure of the population, since colony size was nega- tively correlated with the number of conspecifics breeding within the parental foraging ranges. Therefore, we provide strong evidence suggesting that density-dependent food de-

DISPERSAL AND SOCIAL ATTRACTION AFFECT COLONY SELECTION AND DYNAMICS OF LESSER KESTRELS

We studied the mechanisms that regulate colony dynamics in a Spanish population of Lesser Kestrels, using eight years of data from banded individuals in 494 colony-years. Colony growth was positively related to breeding success at the colony the year before. However, individuals of all dispersal statuses, i.e., adult and first-breeding philopatric and immigrant birds, significantly contributed to changes in colony size, indi- cating an important effect of dispersal on colony dynamics via colony quality. Given that there is strong evidence that Lesser Kestrels base their settlement decisions on conspecifics, we tested whether immigrants used the number of previously settled residents in year t (social or conspecific attraction hypothesis) and/or the breeding performance of conspecifics in year t 2 1 (performance-based attraction hypothesis) to select their breeding colony. Breeding success of colonies varied both in space and time and was autocorrelated from one year to the next. Moreover, lifetime reproductive success of Lesser Kestrels was pos- itively associated with colony size, and individuals can predict final colony size early in the breeding season, so assumptions of both hypotheses were fulfilled. Our results support the social attraction hypothesis, since immigration was positively related to the number of philopatric adults, but not to conspecific breeding success the year before. Given that departure decisions of adults were based on personal information about breeding success and colony size is related to fitness prospects, previously settled individuals provide easy and reliable information about colony quality, and social attraction could be seen as a particular case of public information in Lesser Kestrels. Consistently, absolute numbers of both philopatric adults and immigrants increased with colony size the year before, although immigrants increased only up to a threshold beyond which this trend disappeared. Therefore, immigrants seem to be prevented from settling in the largest colonies, which could explain why all individuals do not concentrate in a few big colonies, but some settle in suboptimal colonies or colonize unoccupied sites. This opposing effect of conspecifics, together with the low levels of temporal autocorrelation in colony quality between time lags

Offspring body condition and immunocompetence are negatively affected by high breeding densities in a colonial seabird: a multiscale approach

2 yr, could promote colony size variability and facultative coloniality in this species.

Ecological, morphological and phylogenetic correlates of interspecific variation in plasma carotenoid concentration in birds

Why avian colonies vary in size and how food competition among nearby colonies affects offspring quality are still not completely understood. We simultaneously examined the effects of four scales of breeding density on two measures of offspring viability (body condition and T–cell–mediated immunity) in the colonial Magellanic penguin. Body condition of fledglings was inversely correlated with breeding density within 100 m2 of nests, and decreased with increasing numbers of breeding pairs competing within the parental foraging ranges (100 km), probably as a result of density–dependent food depletion. The T–cell–mediated immune response was positively correlated with body condition, reflecting, to some extent, the previous breeding–density effects, and was negatively correlated with colony size, which may be related to social stress. However, given the effect of protein intake on cell immunity, this result could also indicate a thus far neglected cost of coloniality, namely the consumption of low–protein food to compensate for the depletion of optimal prey. These results were not influenced by other traits, nor by the current exposure of birds to parasites and diseases, as measured by serological variables. Since body condition and the T–cell–mediated immune response of fledgling birds are indicators of their survival and recruitment prospects, the costs we have identified can explain variability in colony size in relation to food competition with surrounding colonies, as well as the skewed distribution toward small colonies in this species.

The T-cell-mediated immune response and return rate of fledgling American kestrels are positively correlated with parental clutch size.

Carotenoids are important as pigments for bright coloration of animals, and as physiologically active compounds with a wide array of health‐related benefits. However, the causes of variation in carotenoid acquisition and physiology among species are poorly known. We measured the concentration of carotenoids in the blood of 80 wild bird species differing in diet, body size and the extent of carotenoid‐based traits. Preliminary analyses showed that diet significantly explains interspecific variability in plasma carotenoids. However, dietary influences were apparently overridden by phylogenetic relationships among species, which explained most (65%) of this variability. This phylogenetic effect could be due partly to its covariation with diet, but may also be caused by interspecific differences in carotenoid absorption from food to the blood stream, mediated, for example by endothelial carriers or gut parasites. Carotenoid concentrations also decreased with body size (which may be explained by the allometric relationship between ingestion rate and body mass), and correlated positively with the extent of carotenoid‐dependent coloration of plumage and bare parts. Therefore, the acquisition of carotenoids from the diet and their use for both health and display functions seem to be constrained by ecological and physiological aspects linked to the phylogeny and size of the species.

Environmental and genetic variation in T-cell-mediated immune response of fledgling American kestrels

Life–history theory predicts that parents face a trade–off between the number and viability of the progeny they produce. We found evidence for an apparent trade–off in a free–living population of American kestrels (Falco sparverius), as larger clutches produced more but lighter fledglings. However, while the body mass of fledglings has traditionally been used as a measure of survival prospect, offspring immuno–competence should also play an important role. We thus measured the T–cell–mediated immune response of fledgling kestrels in relation to brood traits and nest–rearing conditions through a cross–fostering experiment. The immune response was positively correlated with the body condition of fledglings, but was also higher in those hatched from five–egg than four–egg clutches. These results were not influenced by other brood traits, nor by current exposure to stressors and infectious agents, as measured by sero–logical variables. Such ability to resist pathogens may account for why the probability of offspring returning to the study area in subsequent years, when controlling for brood size, was higher for five–egg than four–egg clutches. These results suggest an optimal clutch size through maternal effects on offspring immunocompetence rather than a trade–off between the number and quality of the offspring.

Genetics, local environment and health as factors influencing plasma carotenoids in wild American kestrels ( Falco sparverius )

Abstract We investigated genetic and environmental components of variance in avian T-cell-mediated immune response (CMI) through a cross-fostering experiment conducted on wild American kestrels (Falco sparverius). CMI was evaluated in vivo by an experimental challenge with phytohaemagglutinin, a T-cell mitogen, injected intradermally in fledglings. Additionally, we assessed two measures of nutritional condition (body mass and circulating plasma proteins) which could influence the variance components of CMI. A two-way nested ANOVA indicated that CMI of fledgling kestrels was explained more by the nest where the bird was reared (33% of the explained variance) than by the nest of origin (12%). Body mass was explained equally by familial and environmental components, while plasma proteins were only related to the rearing environment. CMI of fledglings was not related to their circulating plasma proteins, but was positively correlated with their body mass. Fledgling body mass seemed to be influenced by pre-hatching or post-hatching maternal effects prior to manipulation since resemblance in body mass of sibships at the age of manipulation was high (h2≤0.58), and body mass at this age predicted body mass at fledging. Therefore, pre-manipulation parental effects on body mass, such as investment in egg size, could have inflated the familial effects on body mass of fledglings and then on its correlated CMI. When controlling for body mass, most of the variation in CMI of fledglings was explained by the nest where the bird was reared (36.6%), while the variance explained by the nest of origin (4%) was not significant. This means that environmental influences are major determinants of offspring CMI. The low proportion of variance explained by the familial component may have been due to the high correlation of CMI to fitness.

Diet explains interpopulation variation of plasma carotenoids and skin pigmentation in nestling white storks.

Carotenoids are important as pigments for bright coloration of animals, and as physiologically active compounds with a wide array of health–related functions. Carotenoid–dependent coloration may have evolved as a signal to conspecifics; however, factors that may limit availability of carotenoids are poorly known. We investigated how the acquisition of carotenoids may be constrained by availability in the environment, diet, genetic make–up and health status of wild American kestrels (Falco sparverius). Plasma concentrations of siblings at the time of fledging showed a high degree of resemblance; however, a cross–fostering experiment revealed that variance was largely explained by nest of rearing, rather than nest of origin, thus indicating a low genetic component. A multivariate analysis of attributes of nestlings (sex, size, plasma proteins, immune function), parental reproduction (laying date, clutch size) and rearing conditions (brood size, size hierarchy, nestling mortality) showed only a small significant effect of leucocyte differentials on carotenoid concentrations of nestlings. A strong environmental effect on plasma carotenoids was demonstrated by levels of adult kestrels being correlated within mated pairs, and having a significant association with the abundance of voles, the primary prey species, per territory.