Juan A. Amat

Carotenoids, immune response and the expression of sexual ornaments in male greenfinches (Carduelis chloris)

Allocation trade-offs of carotenoids between their use in the immune system and production of sexual ornaments have been suggested as a proximate mechanism maintaining honesty of sexual signals. To test this idea, we experimentally examined whether carotenoid availability in the diet was related to variation in antibody response to novel antigens in male greenfinches (Carduelis chloris aurantiiventris), a species with extensive carotenoid-dependent plumage colouration. We also measured the cost of mounting a humoral response in terms of circulating carotenoids. Finally, we examined the relationship between plumage colour, immune response and circulating carotenoids. We found that males with carotenoid-supplemented diets showed stronger antibody response than non-supplemented birds. We also found that activation of the immune system significantly reduced circulating carotenoids (24.9% lower in immune-challenged birds than in control birds). Finally, intensity (chroma) of ventral plumage colouration of males, a character directly related to concentration of total carotenoids in feathers, was negatively correlated with the immune response and circulating carotenoids in winter. These results support the idea that carotenoids are a limiting resource and that males trade ornamental colouration against immune response.

How Kentish plovers, Charadrius alexandrinus , cope with heat stress during incubation

Biparental incubation is frequent among shorebirds and is expected when the survival prospects of offspring increase relative to uniparental incubation. To understand why this occurs, it is important to identify the factors that constrain uniparental incubation. It is assumed that birds choose nesting sites that provide an appropriate microclimate for incubation. Many shorebirds nest in sites with no or little cover, where ambient temperatures at ground level might be >50°C during very hot days. Shorebirds nest in exposed sites because predation risk on incubating adults is higher in covered sites. In hot environments, incubating shorebirds might experience heat stress in exposed sites, and this may compromise nesting success if adults are unable to attend their nests continuously, limiting the possibilities of uniparental incubation and thus the expression of a sexual conflict over incubation. The operative temperatures of Kentish plovers (Charadrius alexandrinus) were recorded in exposed and covered sites, and the thermal behaviour and incubating tactics of pair members were studied in a hot environment. During the hottest part of the day, there was a difference of 10–15°C in the operative temperatures of plovers between covered and exposed sites. Plovers in covered sites did not exhibit any thermoregulatory behaviour indicative of thermal stress, probably because the thermal range encountered by them in such places during most of the daytime was close to the thermo-neutral zone. The frequency with which plovers in exposed sites exhibited thermoregulatory behaviour was related to ambient temperature. Under very hot conditions, incubating birds were probably unable to maintain homeostasis for long periods and pair members resorted to shortening incubation bouts. Female Kentish plovers mainly incubate in the daytime and males during the night. However, the probability of diurnal incubation by males increased with ambient temperature in exposed nests, but not in covered ones. In fact, the frequency of participation in diurnal incubation by males was greater in exposed than in covered sites, suggesting that the participation of males in diurnal incubation may be related to the inability of females to stay at the nest during long periods when the ambient temperature is high. Even after resorting to shortened incubation bouts, the plovers may be unable to attend their nests continuously during heat waves, and the nests may be deserted. The propensity of plovers to desert their nests was affected by proximity to water, with nests located close to water being deserted less frequently. It seems likely that susceptibility to thermal stress changed in relation to proximity to water because in sites close to water it was possible to belly-soak, which would allow a more continuous nest attendance. Therefore, despite the adoption of behavioural solutions to face heavy heat loads, nesting success was vulnerable to these solutions because heat stress during extended periods may constrain parental nest attendance, and this may limit the opportunities for sexual conflicts over incubation.

Energetic and developmental costs of mounting an immune response in greenfinches (Carduelis chloris)

It is assumed that there is a trade-off between the costs allocated to mounting an immune defence and those allocated to costly functions such as breeding and moulting. The physiological basis for this is that mounting an immune response to pathogen challenge has energetic and/or nutrient costs which may interfere with metabolic processes of the challenged individual. If the energetic costs of mounting an immune response are not too high, animals may face such costs by increasing their acquisition of food energy, suggesting that limited nutrients may be responsible for the costs of immune defence. We assessed the energetic and developmental costs of mounting an immune response in an experiment in captivity with first-year greenfinches (Carduelis chloris) challenged with sheep red blood cells and Brucella abortus. Antibody production against both antigens increased the daily energy expenditure (4.7%) of immune-challenged birds relative to control birds, although the difference was non-significant. We estimated that the maximum effect size supported by the data would be 9.9% higher in immune-challenged birds relative to control birds. We plucked the two outermost rectrices of each bird to assess the effects of the immune challenge on growth of the regenerated feathers. The immune challenge had no significant effect on the length of the regenerated rectrices. However, these feathers were more asymmetric in length in immune-challenged birds than in control birds. Although first-year male greenfinches paid a relatively low energetic cost when mounting an immune response, we suggest that immune-challenged individuals may have paid some costs over the long term based on the increased fluctuating asymmetry in the developing feathers.

Hatching asynchrony, sibling hierarchies and brood reduction in the Chinstrap penguin Pygoscelis antarctica

We studied patterns of chick growth and mortality in relation to egg size and hatching asynchrony during two breeding seasons (1991 and 1992) in a colony of chinstrap penguins sited in the Vapour Col rookery, Deception Island, South Shetlands. Intraclutch variability in egg size was slight and not related to chick asymmetry at hatching. Hatching was asynchronous in 78% (1991) and 69% (1992) of the clutches, asynchrony ranging from 1 to 4 days (on average 0.9 in 1991 and 1.0 days in 1992). Chicks resulting from oneegg clutches grew better than chicks in families of two in 1991. In 1992, single chicks grew to the same size and mass at 46 days of age as chicks of broods of two, suggesting food limitation in 1991 but not in 1992. In 1991, asymmetry between siblings in mass and flipper length was significantly greater in asynchronous than in synchronous families during the initial guard stage, but these differences disappeared during the later créche phase. In 1992, asymmetry in body mass increased with hatching asynchrony and decreased with age. Only the effect of age was significant for flipper length and culmen. Asymmetries at 15 days were similar in both years, but significantly lower in 1992 than in 1991 at 46 days of age. There were relatively frequent reversals of size hierarchies during both phases of chick growth in the two years, reversals being more common in 1991 than in 1992 for small chicks. In 1991, survivors of brood reduction grew significantly worse than chicks in nonreduced broods. In both years, chicks of synchronous broods attained similarly large sizes before fledging as both A and B chicks of asynchronous broods. In 1991, chick mortality rate increased during the guard stage due to parental desertions, decreased during the transition to crèches (occurs at a mean age of 29 days) and returned to high constant levels during the crèche stage, when it is mostly due to starvation (in total 66% of hatched chicks survived to fledging). In contrast, in 1992, mortality was relatively high immediately after hatching and almost absent for chicks older than 3 weeks (87% of chicks survived to fledging). Mortality affected similarly one- and two-chick families. In 1991, asynchronous families suffered a significantly greater probability of brood reduction than synchronous families, but this probability was not significantly related to degree of asymmetry between siblings. No association between asynchrony and mortality was found in 1992. These results show that there is food limitation in this population during the crèche phase in some years, that asynchronous hatching does not facilitate early brood reduction and that it does not ensure stable size hierarchies between siblings. Brood reduction due to starvation is not associated to prior asymmetry and does not facilitate the survival or improve the growth of the surviving chick. Asynchronous hatching may be a consequence of thermal constraints on embryo development inducing incubation of eggs as soon as they are laid.

Despotic establishment of breeding colonies of greater flamingos, Phoenicopterus ruber, in southern Spain

Abstract. The spatial distribution of individuals fits an ideal despotic distribution (IDD) model when some individuals prevent others from settling in a high-quality habitat, so that the last group of individuals is forced to use lower-quality habitats in which their fitness is lower. A critical assumption of the IDD model is that individuals using the lower-quality habitats must have attempted to settle first in the better habitats, but this has seldom been demonstrated. We tested key assumptions of the IDD model by using long-term data on choice of breeding sites by greater flamingos (Phoenicopterus ruber) in southern Spain, where these birds breed at Fuente de Piedra lake (FP) and the Guadalquivir marshes (GM). Based on the accessibility of terrestrial predators to breeding sites, the FP colony was of better quality than the GM colony. As expected from an IDD model, the flamingos settled first at FP than at GM. The order of settlement was probably not affected by differences in food availability between sites, since in most years, the flamingos breeding in FP obtained food in GM during the chick-rearing period, once the FP lake dried up. Furthermore, breeding success was much higher at FP than at GM. Another assumption of the model is that individuals are omniscient and that they should try to settle first in the best site. We recorded 18 individually marked flamingos prospecting for nest sites in FP in a season, when many birds had already settled in this colony. The same individuals were subsequently recorded breeding in the same season in GM, indicating that they had previous information on the availability of sites on which to breed. A third assumption of the IDD model is that as the density increases in a given habitat, the fitness of individuals should decrease. In accordance with this, we found a strong effect of bird density on egg losses. The individuals that were recorded prospecting for sites in FP and that later bred in GM were younger than flamingos that were breeding in FP. We suggest that age-related behavioral dominance may be a mechanism responsible for this despotic distribution.

Replacement clutches by Kentish plovers

We examined factors affecting renesting rates in a population of Kentish Plovers (Charadrius alexandrinus) in southern Spain over six breeding seasons. We show that renesting was mainly constrained by time, and not by female body condition. Renesting partially compensated for initial clutch losses. The interval from loss of the first clutch to initiation of the replacement clutch was not affected by the number of days of incubation preceding nest loss. Renesting plovers moved considerable distances from first nests. Distances moved between nesting attempts by pairs that had lost chicks were similar to those of pairs that lost eggs. Nest cover did not differ between first and second nests when the first nest was successful, but it was greater in second nests when the first nest was unsuccessful. Yet, nest cover had no influence on the fate of such replacement clutches, probably due to a high diversity of predators at our study site. Females that laid replacement clutches did not delay breeding or breed less frequently in years after they had laid replacement clutches. Even when the success of replacement clutches is moderate, this breeding strategy may be important in accounting for individual lifetime productivity, especially when nest predation is high, as in the studied population.

Greater flamingos Phoenicopterus roseus use uropygial secretions as make-up

It was long thought that the colour of bird feathers does not change after plumage moult. However, there is increasing evidence that the colour of feathers may change due to abrasion, photochemical change and staining, either accidental or deliberate. The coloration of plumage due to deliberate staining, i.e. with cosmetic purposes, may help individuals to communicate their quality to conspecifics. The presence of carotenoids in preen oils has been previously only suggested, and here we confirm for the first time its presence in such oils. Moreover, the carotenoids in the uropygial secretions were the same specific pigments found in feathers. We show not only that the colour of feathers of greater flamingos Phoenicopterus roseus became more colourful due to the application of carotenoids from uropygial secretions over the plumage but also that the feathers became more colourful with the quantity of pigments applied over them, thus providing evidence of cosmetic coloration. Flamingos used uropygial secretions as cosmetic much more frequently during periods when they were displaying in groups than during the rest of the year, suggesting that the primary function of cosmetic coloration is mate choice. Individuals with more colourful plumage initiated nesting earlier. There was a correlation between plumage coloration before and after removal of uropygial secretions from feathers’ surfaces, suggesting that the use of these pigmented secretions may function as a signal amplifier by increasing the perceptibility of plumage colour, and hence of individual quality. As the cosmetic coloration strengthens signal intensity by reinforcing base-plumage colour, its use may help to the understanding of selection for signal efficacy by making interindividual differences more apparent.

Daily variations of blood chemistry values in the chinstrap penguin (Pygoscelis antarctica) during the Antarctic summer

We investigated the daily variations of blood chemistry during the 1990-91 Antarctic smnmer solstice in six adult chinstrap penguins (Pugoscefis antarctica) in the absence of eat-fast cycles. Four of the seven blood parameters (glucose, urea, triglyceride and cholesterol) showed statistically sign&ant variations between samples at periods of different light intensity. Blood chemistry changes in chinstrap penguins correspond with those expected in a diurnal bird under defined light-dark cycle. In the absence of eat-fast cycle, the daily cycle of light intensity, although greatly attenuated, is the most likely timekeeper (Zeitgeber) for circadian rhythms in blood parameters of chinstrap penguins.

High gene flow on a continental scale in the polyandrous Kentish plover Charadrius alexandrinus

Gene flow promotes genetic homogeneity of species in time and space. Gene flow can be modulated by sex‐biased dispersal that links population genetics to mating systems. We investigated the phylogeography of the widely distributed Kentish plover Charadrius alexandrinus. This small shorebird has a large breeding range spanning from Western Europe to Japan and exhibits an unusually flexible mating system with high female breeding dispersal. We analysed genetic structure and gene flow using a 427‐bp fragment of the mitochondrial (mtDNA) control region, 21 autosomal microsatellite markers and a Z microsatellite marker in 397 unrelated individuals from 21 locations. We found no structure or isolation‐by‐distance over the continental range. However, island populations had low genetic diversity and were moderately differentiated from mainland locations. Genetic differentiation based on autosomal markers was positively correlated with distance between mainland and each island. Comparisons of uniparentally and biparentally inherited markers were consistent with female‐biased gene flow. Maternally inherited mtDNA was less structured, whereas the Z‐chromosomal marker was more structured than autosomal microsatellites. Adult males were more related than females within genetic clusters. Taken together, our results suggest a prominent role for polyandrous females in maintaining genetic homogeneity across large geographic distances.

Waterbirds as Bioindicators of Environmental Conditions

We give examples of how waterbirds can be valuable indicators of changes in aquatic systems. Eutrophication is a widespread problem that can increase the food supply for some birds and hence increase their population size (e.g. great-crested grebes). Many birds are sensitive to changes in water depth, and some can decline due to siltation of shallow lakes (e.g. red-knobbed coot) or when low rainfall leads temporary wetlands to dry out (e.g. greater flamingos). The species-richness of the waterbird community is a less reliable indicator than trends for a given species, and has a weak relationship with the richness of other aquatic communities. As well as indicating changes in conditions, waterbirds can also cause them when they reach high densities, e.g. when colonial birds import nutrients from elsewhere or when geese cause overgrazing. When using waterbirds as indicators, a thorough knowledge of their ecology and clear objectives for the monitoring programme are essential.