Herbert Hoi

Food availability and immune capacity in serin (Serinus serinus) nestlings

Abstract. Parental feeding effort is an important determinant of chick development in birds. Quality and amount of food provided to each nestling, however, might affect the development of the immune system. Food availability around the nest site may account for part of the difference in body condition and immune capacity of nestlings. We tested this idea in the socially monogamous serin (Serinus serinus), investigating growth and immune capacity of nestlings in relation to food availability around the nest site. We used a set of immunological and serological assays, including antibody responses to sheep red blood cells (SRBCs), the T lymphocyte cell-mediated immune response (PHA), granulocyte:lymphocyte ratio (G:L), haematocrit and sedimentation rate. The results suggest that serins raised under poor environmental conditions were less immunocompetent. The immune response to PHA and SRBCs significantly increased with food availability. Haematocrit values were positively, sedimentation rate and the G:L ratio negatively correlated with food availability. Similar results were obtained when examining chick development in relation to the immunological and serological variables. However, there was a negative relationship between parental feeding rates and food availability, as well as between parental feeding rates and chick development. We conclude that body condition and immune capacity of nestlings are strongly correlated with the availability of food around the nest site.

Predation on nests: a case of apparent competition

We describe a field experiment designed to evaluate indirect effects in a prey community sharing common predators. A simple prey community was mimicked with two types of artificial nests. Firstly, it was shown that predation rate increased with nest density when only a single prey was present. Secondly, it was shown that an increase in the density of one nest type increased the predation rate on another type. This is the first experimental evidence for indirect effects in vertebrate communities, which also may help to explain the strong interspecific aggression observed in some communities. In a previous treatment we had shown that there is no observer effect on nest predation in the form of density-dependent scent marking while laying out the artificial nests.

Preening, plumage reflectance and female choice in budgerigars

Plumage ornaments are important signals in sexual selection context. Plumage maintenance is therefore important not only for insulation and flight but also for ornament efficacy. However, the effect of plumage maintenance on ornament characteristics and female choice has never been investigated experimentally. In this study we focused on the influence of preening on plumage reflectance and, indirectly, on female preference in the budgerigar Melopsittacus undulatus. We measured the effect of preening on the reflectance of previously soiled plumage. Our results suggest that soiling affects plumage reflectance in budgerigars that are prevented from preening and that this effect is particularly pronounced in the UV range. In contrast, individuals that were allowed to preen restored their plumage reflectance spectrum to presoiling levels. In a two-choice test, females presented with clean (preened) and soiled (unpreened) males, spent more time near the clean male. These results suggest that female budgerigars are able to discriminate between preened and unpreened males. Further investigations, conducted under various soiling conditions, are necessary to confirm the effect of soiling on plumage reflectance spectrum and to investigate which cues are used by females to discriminate between preened and unpreened males. Such research could reveal whether UV feather ornaments, mediated by preening, are special signals conveying information about a birds current condition.

INTERSPECIFIC PARASITE EXCHANGE IN A MIXED COLONY OF BIRDS

Studies of avian host–parasite interactions rarely include consequences of relationships among hosts for either the host or parasite species. In this study, we examine the ectoparasitic burden of adult and nestling European bee-eaters (Merops apiaster) and rock sparrows (Petronia petronia) in a mixed colony. We found that (1) each bird species had its own species of lice; (2) hematophagous mites parasitized both adults and nestlings of both bird species; (3) Carnus hemapterus, a common parasite of nestling bee-eaters, also infested rock sparrow nestlings, a species not previously described as a host for this dipteran; and (4) whereas C. hemapterus did not show high host specificity within the colony, the emergence of adult flies was synchronized with the start of hatching in bee-eater nests. We suggest that coexistence of these 2 bird species results in parasite exchange, bee-eaters obtaining mites from sparrows and sparrows becoming infested by C. hemapterus. Differences in the detrimental effects of parasite transfer for each host species may result in a process of apparent competition mediated by shared parasites. Interspecific parasite exchange is an important aspect of host–parasite relationships in mixed colonies, which requires further attention.

Alarm calls and chick reactions in the moustached warbler,Acrocephalus melanopogon

As in many altricial species, adult moustached warblers alarm call more at the nest as the breeding season progresses. This study used the experimental human approach method as well as two predator types (plastic snake and taxidermic raptor) placed at the nest to test the anti-predator responses of chicks to parental alarm calls. The probability of chicks making anti-predator responses (ducking and jumping) was strongly correlated with the probability of adults giving alarm calls. Furthermore, chicks reacted selectively to different predator types, tending to remain in the nest in response to aerial predators and to jump from the nest in response to ground predators. A conceptual framework is presented identifying the age of chicks when alarm calls are first given for the brood value, vulnerability and chick reaction hypotheses. These were tested by comparing the intercept of the regression line for alarm calls with those predicted by each hypothesis. The results suggest that the anti-predator response of chicks is the proximate cue for adult alarm calls.

Assessment of the quality of copulation partners in the monogamous bearded tit

Abstract Females try to control paternity in various ways. They may resist copulation attempts by males but they may also feign resistance in order to incite competition between males. In the lifetime monogamous bearded tit,Panurus biarmicuschase-flights, both within pairs and with other males, occur during the females fertile period. In general, these chase-flights are followed by copulations. Females in this study were able to resist copulations, but they also often approached males and solicited copulations by wing flapping; if males tried to mount the females, they resisted and flew away. During the fertile period females solicited extra-pair males to chase them significantly more often than they solicited chases with their own mate. In isolated pairs chase-flight activity was reduced and most copulations occurred without preceding chase-flights. In addition, females in isolated pairs solicited their partners to chase them significantly less often than females with extra males available. This suggests that females use chases to incite male–male competition and thus to obtain ‘good genes’. In contrast to other studies, females paired to high-ranking males incited more chase-flights than females paired to low-ranking males, perhaps because only high-quality females could afford to perform this energetically expensive activity.

Female ornamentation, parental quality, and competitive ability in the rock sparrow

The evolution of female ornaments is poorly understood. Recent evidence suggests not only that female ornaments may be genetic correlates of selection on males but may also have evolved through male mate choice and/or through female–female aggressive interactions. In the rock sparrow, Petronia petronia, both sexes have a carotenoid-based yellow patch that is sexually selected by both sexes. The benefits that male may gain from choosing an attractive female remain unidentified. Both parents participate in caring for the young, so there should be mutual mate choice because males and females should both benefit from choosing a good parent (good parent hypothesis; GPH). Moreover, it has already been demonstrated that the yellow patch in males is also a badge of status (armament). Therefore, the yellow patch could also serve as both ornament and armament in females (dual utility hypothesis; DUH). We investigated the hypothesis that male and female yellow patch size signals parental quality in the field. We tested by an experiment in captivity the signal function of the yellow patch in female–female aggressive interactions for access to food. Yellow patch size correlated with paternal, but not maternal, feeding rates. Thus, this study supports the hypothesis that yellow patch dimension signals male parental quality, but there is no evidence for the GPH to explain female ornamentation. In the experiment females with relatively large yellow patches had earlier access to food than those with small patches. These results seem to suggest that a sexually selected carotenoid-feather signal may be used in female–female competition, in agreement with the DUH. Males may benefit from choosing well ornamented females because these may be superior competitors.

UV plumage color is an honest signal of quality in male budgerigars

Elaborate and colorful feathers are important traits in female mate choice in birds. Plumage coloration can result from pigments deposited in feathers such as carotenoids and melanins, or can be caused by nano-scale reflective tissues (structurally based coloration), usually producing ultraviolet (UV) coloration. Structural colorations remain the least studied of the three most important feather colorations. Previous studies have found a female preference for UV color in the budgerigar, Melopsittacus undulatus, but it is not clear what information this ornament conveys, nor what is the possible cost associated with its production. We investigated possible correlations between immune response and plumage color of wild-type (green) male budgerigars. In particular we measured the wing web swelling resulting from injection of phytohaemagglutinin (PHA). We did not detect any correlation between the sedimentation rate and morphological and color variables. We found that UV chroma is the best predictor for the cutaneous immune activity. Indeed, male budgerigars with high UV reflectance in the breast feathers showed stronger immune responses. These results are consistent with the idea that UV colors are special signals conveying information about a bird’s condition.

Female attractiveness affects paternal investment: experimental evidence for male differential allocation in blue tits

IntroductionThe differential allocation hypothesis (DAH) predicts that individuals should adjust their parental investment to their current mate’s quality. Although in principle the DAH holds for both sexes, male adjustment of parental investment has only been tested in a few experimental studies, revealing contradictory results. We conducted a field experiment to test whether male blue tits (Cyanistes caeruleus) allocate their parental effort in relation to female ornamentation (ultraviolet colouration of the crown), as predicted by the DAH.ResultsWe reduced the UV reflectance in a sample of females and compared parental care by their mates with that of males paired to sham-manipulated control females. As predicted by the DAH our results demonstrate that males paired with UV-reduced females invested less in feeding effort but did not defend the chicks less than males paired with control females.ConclusionsTo our knowledge, this is one of the first studies providing support for male differential allocation in response to female ornamentation.

HORIZONTAL AND VERTICAL ECTOPARASITE TRANSMISSION OF THREE SPECIES OF MALOPHAGA, AND INDIVIDUAL VARIATION IN EUROPEAN BEE-EATERS (MEROPS APIASTER)

Dispersal of avian ectoparasites can occur through either vertical transmission from adult birds to their offspring in the nest or through horizontal transmission between adult birds or through phoresy. In this study, we investigated the importance of the 2 main transmission modes in the colonial European bee-eater and examined whether individual differences in ectoparasite intensity exist in relation to age, sex, and morphological features of the birds. The intensity of 3 chewing lice species was investigated. Almost all adult bee-eaters (98.3%, n = 176) were infested with 1 of the 3 ectoparasite species, whereas only 10.8% (n = 167) of all chicks were infested. Meropoecus meropis was the most frequent ectoparasite species on adult bee-eaters (prevalence 94.3%), whereas Meromenopon meropis was the most common species on chicks (prevalence 9.6%). Our results suggest that chewing lice are mainly horizontally transmitted among adult bee-eaters and mainly among pair members, whereas vertical transmission between parents and nestlings is less frequent. These conclusions were supported by a relation in ectoparasite intensity of pair members and a parasite removal experiment. Ectoparasite intensity was in general low in nestlings and did not correlate with ectoparasite intensity of their parents. Host age, sex, weight, and other morphological features did not explain variation in chewing lice infestation.