F. Uribe

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

Status signalling, metabolic rate and body mass in the siskin: the cost of being a subordinate

The higher metabolic rate of dominant individuals, found in different species, has been interpreted as the cost that prevents subordinates from cheating by adopting large badges of status. However, an alternative prediction for status-signalling species, in which subordinates may recognize dominants, is that subordinates have the higher metabolic rate because of the greater stress of locating and actively avoiding aggressive interactions with them. In this study, the size of the black bib of the siskin, Carduelis spinus, which is a badge of dominance, was negatively correlated with metabolic rate in daylight, even when controlling for the birds activity level in the respirometer chamber and its body mass. The size of the black bib, however, was not correlated with metabolic rate in darkness. This suggests that the difference between dominance classes is not related to intrinsic physiological differences, but that subordinates are more susceptible to stressful conditions. When controlling for metabolic rate, a positive correlation appeared between dominance status and body mass. This stresses the importance of knowing the effects of social status on energy requirements for understanding the relationship between body mass and dominance. We conclude that maintaining a high social status may be more stressful to subordinates than to dominant birds. Copyright 2000 The Association for the Study of Animal Behaviour.

Familiarity adds to attractiveness in matters of siskin mate choice

There is currently considerable controversy in evolutionary ecology revolving around whether social familiarity brings attraction when a female chooses a mate. The topic of familiarity is significant because by avoiding or preferring familiar individuals as mates, the potential for local adaptation may be reduced or favoured. The topic becomes even more interesting if we simultaneously analyse preferences for familiarity and sexual ornaments, because when familiarity influences female mating preferences, this could very significantly affect the strength of sexual selection on male ornamentation. Here, we have used mate-choice experiments in siskins Carduelis spinus to analyse how familiarity and patterns of ornamentation (i.e. the size of wing patches) interact to influence mating success. Our results show that females clearly prefer familiar individuals when choosing between familiar and unfamiliar males with similar-sized wing patches. Furthermore, when females were given the choice between a highly ornamented unfamiliar male and a less ornamented familiar male, half of the females still preferred the socially familiar birds as mates. Our finding suggests that male familiarity may be as important as sexual ornaments in affecting female behaviour in mate choice. Given that the potential for local adaptation may be favoured by preferring familiar individuals as mates, social familiarity as a mate-choice criterion may become a potential area of fruitful research on sympatric speciation processes.