Juan Carlos Senar

Status signalling and the ability to recognize dominants: an experiment with siskins (Carduelis spinus)

Because dominants usually exploit others and take a disproportionate share of the available resources, we should expect foragers to be choosy as to which individuals they join. Here we show that siskins (Carduelis spinus) discriminate between dominant and subordinate individuals on the first encounter without requiring cues such as overt aggression, and prefer to join subordinate individuals. Experimental enlargement or removal of the siskin black bib, which has been shown previously to be a reliable predictor of dominance, strongly suggests that dominance discrimination is based on the use of badges of status.

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

Brominated flame retardants and organochlorines in the European environment using great tit eggs as a biomonitoring tool

Large-scale studies are essential to assess the emission patterns and spatial distribution of organohalogenated pollutants (OHPs) in the environment. Bird eggs have several advantages compared to other environmental media which have previously been used to map the distribution of OHPs. In this study, large-scale geographical variation in the occurrence of OHPs, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides (OCPs), was investigated throughout Europe using eggs of a terrestrial residential passerine species, the great tit (Parus major). Great tit eggs from 22 sampling sites, involving urban, rural and remote areas, in 14 European countries were collected and analysed (5-8 eggs per sampling site). The environmentally most important congeners/compounds of the analysed pollutants were detectable in all sampling locations. For PCBs, PBDEs and OCPs, no clear geographical contamination pattern was found. Sum PCB levels ranged from 143 ng/g lipid weight (lw) to 3660 ng/g lw. As expected, PCB concentrations were significantly higher in the sampled urban compared to the remote locations. However, the urban locations did not show significantly higher concentrations compared to the rural locations. Sum PBDEs ranged from 4.0 ng/g lw to 136 ng/g lw. PBDEs were significantly higher in the urbanized sampling locations compared to the other locations. The significant, positive correlation between PCB and PBDE concentrations suggests similar spatial exposure and/or mechanisms of accumulation. Significantly higher levels of OCPs (sum OCPs ranging from 191 ng/g lw to 7830 ng/g lw) were detected in rural sampling locations. Contamination profiles of PCBs, PBDEs and OCPs differed also among the sampling locations, which may be due to local usage and contamination sources. The higher variance among sampling locations for the PCBs and OCPs, suggests that local contamination sources are more important for the PCBs and OCPs compared to the PBDEs. To our knowledge, this is the first study in which bird eggs were used as a monitoring tool for OHPs on such a large geographical scale.

Variation in black bib of the Eurasian Siskin (Carduelis spinus) and its role as a reliable badge of dominance

Rohwer (1975, 1982) proposed that the variation and extent of color patches in the plumage of wintering birds could work as badges of social status. The major advantage of these signals would be that individuals of unequal status competing for limited resources would not need to risk accidental injury or waste energy assessing the relative fighting ability of potential opponents (Rohwer 1982). The status-signalling hypothesis has been tested in several species with variable plumage (reviewed by Whitfield 1987; see also Amat 1986, Watt 1986a, b, Fugle and Rothstein 1987, Moller 1987a, b,1989, Jackson et al. 1988). These studies have, however, produced contradictory results. For plumage differences to act as true badges of dominance, they should correlate within and not just between sex and age classes. This has been demonstrated in only a few species (Great Tit [Parus major], Jarvi and Bakken 1984; Yellow Warbler [Dendroica petechia], Studd and Robertson 1985; House Sparrow [Passer domesticus], Meller 1987a; Whitfield 1987; see however Ritchison 1985, Poysa 1988, Wilson 1992). The Eurasian Siskin (Carduelis spinus) shows great variability in the extent of blackish plumage in the bib (Newton 1972). This chin patch, as in House Sparrows (Moller 1987a), is present only in males, which are dominant over females. Dominance, however, is unaffected by age (Senar 1985). This lack of a relationship between age and dominance, and the absence of the badge in females simplifies analysis of the significance of the chin patch in status signalling. Other features in the Eurasian Siskin plumage also could be used for dominance signalling. For instance, yellow wing stripes have been found to work as a badge of status in its American counterpart, the Pine Siskin (Carduelis pinus; Balph and Balph unpubl. paper); they could have an important role. However, since wings are displayed in only 25% of the agonistic displays used by the Eurasian Siskin (Senar 1990), the chin is always visible, and most of the encounters between unfamiliar birds in wild flocks are between males (i.e. the badged individuals; Senar et al. 1990b), we restricted this analysis to the black bib. We describe variation in the size of the chin patch in male Eurasian Siskins and test (both in captivity and in the field) whether this variation is related to dominance status. Methods.-Plumage variability and dominance relations in the field were studied in a suburban area of Barcelona (NE Spain) during the 1990-1991 winter. Birds were trapped at baited feeders using platform traps and clap nets, and were marked with numbered aluminium bands. Trapping was carried out at least twice weekly, but the food was available continually so that Eurasian Siskins used the area heavily. For each male siskin we recorded, whenever possible, age and the maximum length and breadth of the badge. Badge size was measured by tilting the birds head back in line with the body. Following the procedure of Moller (1987a), we determined the relationship between badge area, length (L, mm) and breadth (B, mm) from 12 museum skins. Thus, badge area (A, mm) was calculated as:

STATE-SPECIFIC DETECTION PROBABILITIES AND DISEASE PREVALENCE

Investigations of disease dynamics in wild animal populations often use estimated prevalence or incidence as a measure of true disease frequency. Such indices, almost always based solely on raw counts of infected and uninfected individuals, are often used as the basis for analysis of temporal and spatial dynamics of diseases. Generally, such studies do not account for potential differences in observer detection probabilities of host individuals stratified by biotic and/or abiotic factors. We demonstrate the potential effects of heterogeneity in state-specific detection probabilities on estimated disease prevalence using mark-recapture data from previous work in a House Finch (Carpodacus mexicanus) and Mycoplasma gallisepticum system. In this system, detection probabilities of uninfected finches were generally higher than infected individuals. We show that the magnitude and seasonal pattern of variation in estimated prevalence, corrected for differences in detection probabilities, differed markedly from uncorrected (apparent) prevalence. When the detection probability of uninfected individuals is higher than infected individuals (as in our study), apparent prevalence is negatively biased, and vice versa. In situations where state-specific detection probabilities strongly interact over time, we show that the magnitude and pattern of apparent prevalence can change dramatically; in such cases, observed variations in prevalence may be completely spurious artifacts of variation in detection probability, rather than changes in underlying disease dynamics. Accounting for differential detection probabilities in estimates of disease frequency removes a potentially confounding factor in studies seeking to identify biotic and/or abiotic drivers of disease dynamics. Given that detection probabilities of different groups of individuals are likely to change temporally and spatially in most field studies, our results underscore the importance of estimating and incorporating detection probabilities in estimated disease prevalence (specifically), and more generally, any ecological index used to estimate some parameter of interest. While a mark-recapture approach makes it possible to estimate detection probabilities, it is not always practical, especially at large scales. We discuss several alternative approaches and categorize the assumptions under which analysis of uncorrected prevalence may be acceptable.

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.

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.

Specific appetite for carotenoids in a colorful bird.

Background Since carotenoids have physiological functions necessary for maintaining health, individuals should be selected to actively seek and develop a specific appetite for these compounds. Methodology/Principal Findings Great tits Parus major in a diet choice experiment, both in captivity and the field, preferred carotenoid-enriched diets to control diets. The food items did not differ in any other aspects measured besides carotenoid content. Conclusions/Significance Specific appetite for carotenoids is here demonstrated for the first time, placing these compounds on a par with essential nutrients as sodium or calcium.

Population differentiation and restricted gene flow in Spanish crossbills: not isolation-by-distance but isolation-by-ecology.

Divergent selection stemming from environmental variation may induce local adaptation and ecological speciation whereas gene flow might have a homogenizing effect. Gene flow among populations using different environments can be reduced by geographical distance (isolation‐by‐distance) or by divergent selection stemming from resource use (isolation‐by‐ecology). We tested for and encountered phenotypic and genetic divergence among Spanish crossbills utilizing different species of co‐occurring pine trees as their food resource. Morphological, vocal and mtDNA divergence were not correlated with geographical distance, but they were correlated with differences in resource use. Resource diversity has now been found to repeatedly predict crossbill diversity. However, when resource use is not 100% differentiated, additional characters (morphological, vocal, genetic) must be used to uncover and validate hidden population structure. In general, this confirms that ecology drives adaptive divergence and limits neutral gene flow as the first steps towards ecological speciation, unprevented by a high potential for gene flow.