Jordi Domènech

Plumage coloration and nutritional condition in the great tit Parus major: the roles of carotenoids and melanins differ.

The size and coloration of some body characters seem to influence mate choice in many species. Most animal colours are either structural or based on melanin or carotenoid pigments. It has recently been suggested that carotenoid-based or structural coloration may be a condition-dependent trait, whereas melanin-based coloration is not; a difference that may be highly relevant when studying the evolution of multiple mating preferences. We tested this hypothesis in the great tit (Parus major). The size of the melanin breast band was not correlated to nutritional condition as estimated by the rate of tail growth (ptilochronology), controlling for locality, age, sex, year and season effects. However, the correlation was significant for the hue of yellow breast (carotenoid-based coloration), and the slopes of the regressions of the two pigments to growth bars differed significantly. These results suggest that the expression of the two traits may be regulated by different mechanisms.

Interactions among environmental stress, body condition, nutritional status, and dominance in great tits

Body condition and feather growth rate of Great Tits ( Parus major) were studied in relation to dominance in two contrasting Mediterranean localites during late autumn and early winter. The two localities differed in altitude, ambient temperatures (100 vs 1500 m a.s.l., and 11.7 oC vs 4.6 oC, respectively) and arthropod availability. The two study areas were similarly food supplemented (husked peanuts) throughout the study period. Percentage of time spent at feeders was higher at El Ventorrillo (the locality with colder climate and less natural food availability), and was associated with dominance only in this locality. Number of aggressive displacements per hour suffered by each individual was higher (150-fold greater) in the area with less arthropod availability and lower temperatures. Protein reserves measured as pectoralis muscle thickness was higher at El Ventorrillo, and was positively and consistently related to dominance in both localities. Growth rate of induced feathers was slower in the locality that was colder and had less natural food availability (El Ventorrillo), but was not clearly and directly related to dominance in both localities. Only dominant adult males in El Ventorrillo could compensate the higher environmental harshness of this locality attaining a higher feather growth rate than the other sex-age classes. Feather mass asymmetry during autumn was not associated with body condition, did not change between localities, and was inversely and consistently related to dominance in both localities. The covariation pattern among variables describing bird size, access to supplemented food, body condition, feather growth rate and asymmetry was different in both localities. Only in the locality with colder temperatures and lower arthropod food availability (El Ventorrillo) larger, more dominant, Great Tits spent more time foraging on feeders, had a thicker pectoralis muscle (i.e. body condition), and grew the induced feathers at a higher rate. pmajor

Plumage colour is related to ectosymbiont load during moult in the serin, Serinus serinus: an experimental study

Various hypotheses propose that plumage ornamentation is a reliable indicator of the health or resistance to parasites and illness of individuals. The impact of endoparasites on plumage brightness has only recently been demonstrated experimentally. We tested the impact of ectosymbionts, in particular feather mites, on plumage brightness, using 2 years of observational data and experiments in the field. The abundance of feather mites during moult was negatively correlated with brightness and saturation of plumage coloration developed by male serins. The application of an insecticide before moult resulted in experimental males developing a brighter plumage than control individuals. Experimental adult males, but not juveniles, also developed more saturated plumages in one of the years, but did not differ from controls in the other year. This is the first experimental demonstration that ectosymbionts (including mites) have a negative impact on the characteristics of the plumage developed and consequently can signal the healthiness of their hosts.  2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Analysis of individual- and time-specific covariate effects on survival of Serinus serinus in north-eastern Spain

We developed models for the analysis of recapture data for 2678 serins ( Serinus serinus ) ringed in north-eastern Spain since 1985. We investigated several time- and individual-specific factors as potential predictors of overall mortality and dispersal patterns, and of gender and age differences in these patterns. Time-specific covariates included minimum daily temperature, days below freezing, and abundance of a strong competitor, siskins ( Carduelis spinus ) during winter, and maximum temperature and rainfall during summer. Individual covariates included body mass (i.e. body condition), and wing length (i.e. flying ability), and interactions between body mass and environmental factors. We found little support of a predictive relationship between environmental factors and survival, but good evidence of relationships between body mass and survival, especially for juveniles. Juvenile survival appears to vary in a curvilinear manner with increasing mass, suggesting that there may exist an optimal mass beyond which increases are detrimental. The mass-survival relationship does seem to be influenced by at least one environmental factor, namely the abundance of wintering siskins. When siskins are abundant, increases in body mass appear to relate strongly to increasing survival. When siskin numbers are average or low the relationship is largely reversed, suggesting that the presence of strong competition mitigates the otherwise largely negative aspects of greater body mass. Wing length in juveniles also appears to be related positively to survival, perhaps largely due to the influence of a few unusually large juveniles with adult-like survival. Further work is needed to test these relationships, ideally under experimentation.

Plumage brightness, vigilance, escape potential, and predation risk in male and female Eurasian Siskins (Spinus spinus)

ABSTRACT According to the “sexual selection hypothesis” (SSH), plumage conspicuousness has evolved through mate choice because it signals the quality of the bearer, and this is an honest signal because it involves a predation cost in terms of increased detectability to predators. Alternatively, according to the “unprofitable prey hypothesis” (UPH), conspicuousness is an aposematic signal indicating higher escape potential. We should expect the animals with higher predation risk (either conspicuous or dull, depending on the hypothesis) to have evolved antipredator behaviors to compensate for their higher predation risk (i.e. the “compensation hypothesis”). We tested these hypotheses by studying the vigilance behavior of wintering Eurasian Siskins (Spinus spinus) foraging on three feeders with different predation-risk and competition levels. Males were, on average, 50% more brightly colored than females. Males and females had similar wing loading, which allows us to reject male unprofitability related to higher takeoff speed. Males had shorter mean interscan durations (which improves predator detection) than females, especially at the high-predation-risk feeder (which males avoided), but the sexes did not differ in foraging-bout length, percentage of time spent scanning, and mean scan duration. In males, length of yellow tail stripe and brightness were positively correlated with percentage of time spent scanning. Therefore, our results on vigilance behavior and wing loading support the compensation hypothesis and the SSH assumption of a predation cost of conspicuousness, whereas they reject the predictions of the UPH. Compensation vigilance and other antipredator behaviors are expected to have also evolved in the conspicuous sex in other dichromatic species, and we predict that a correlation between plumage conspicuousness and vigilance should be found in future comparative studies.