Deseada Parejo

Sex recognition by odour and variation in the uropygial gland secretion in starlings

1. Although a growing body of evidence supports that olfaction based on chemical compounds emitted by birds may play a role in individual recognition, the possible role of chemical cues in sexual selection of birds has been only preliminarily studied. 2. We investigated for the first time whether a passerine bird, the spotless starling Sturnus unicolor, was able to discriminate the sex of conspecifics by using olfactory cues and whether the size and secretion composition of the uropygial gland convey information on sex, age and reproductive status in this species. 3. We performed a blind choice experiment during mating, and we found that starlings were able to discriminate the sex of conspecifics by using chemical cues alone. Both male and female starlings preferred male scents. Furthermore, the analysis of the chemical composition of the uropygial gland secretion by using gas chromatography-mass spectrometry (GC-MS) revealed differences between sexes, ages and reproductive status. 4. In conclusion, our study reveals for first time that a passerine species can discriminate the sex of conspecifics by relying on chemical cues and suggests that the uropygial gland secretion may potentially function as a chemical signal used in mate choice and/or intrasexual competition in this species.

Do avian brood parasites eavesdrop on heterospecific sexual signals revealing host quality? A review of the evidence

Eavesdropping can be defined as the extraction of information from the interactions between other individuals. It provides a relatively cheap way of gathering relevant information for fitness enhancement. Here, we propose that obligate avian brood parasites, which always lay their eggs in foreign nests of individuals of other species, may eavesdrop on their host sexual signals to locate nests of high quality individuals in which to lay their parasitic eggs. Sexual signal variation can honestly signal parental quality. Thus, by eavesdropping on sexual signals, parasites may select high quality foster parents for their own offspring. Such a use of sexual signals within host populations by brood parasites differs from signal exploitation theory that proposes that parasite only use signals to locate potential host independently from signaller quality. Here, we review the avian literature concerning host choice within a host species by obligate avian brood parasites and find evidence for host selection within individuals of a host species on the basis of cues potentially functioning as sexually selected traits, or at least revealing parental abilities. We have also found support for the existence of benefits linked to host selection by avian brood parasites. Finally, one study reported on the attenuation of a sexual ornament in host populations under strong pressure by brood parasites. Most of these findings have been interpreted as evidence for host selection by avian brood parasites based on the conspicuousness of sexual signals. We suggest, however, that these findings may in fact reveal eavesdropping on host signalling performance by brood parasites which would use the information extracted to choose the better individuals among conspecifics of a given host. This provides a new perspective for the study of host selection in obligate brood parasites, and raises interesting questions for the study of animal cognition that would deserve experimental studies.

Colony-site Tenacity and Egg Color Crypsis in the Gull-billed Tern

Abstract Colony-site tenacity commonly reflects the stability of nesting habitats. The match between nesting substrate and coloration pattern of the eggs in two reproductive groups of the Gull-billed Tern (Gelochelidon nilotica) in the south of Iberian Peninsula was investigated to tests the adaptiveness of colony-site tenacity. The terns showing high colony-site tenacity had 1) a closer match in color between the eggs and the nesting substrate and 2) a lower richness and diversity of egg colors and 3) a lower rate of egg loss from predation than the low colony-site tenacity ones. These results appear to be adaptive, resulting from a long-standing renesting in the same colony-site. However, such mimicry would be difficult to achieve for terns with low site-tenacity, where breeding occur in unstable habitats. These birds were frequently obliged to move from one location to another due to weather irregularity and water level in the reservoirs they bred. In addition, the occasional high predation pressures on both adults and chicks, manifested by the low-tenacity tern group studied, was also involved. The attainment of such egg-crypsis could be an important adaptive advantage favoring colony-site tenacity. In unstable habitats, however, there would be a trade-off between the benefits linked to colony-site tenacity and the negative effects of suboptimal reproduction. Additional experimental design and studies are, however, necessary to confirm these results and predictions.

Visual cues and parental favouritism in a nocturnal bird

Visual signals are crucial for parent–offspring communication, although their functioning has been neglected for nocturnal birds. Here, we investigated parental preference for nestling coloration in nocturnal conditions—a question hitherto unexplored—in a nocturnal raptor, the scops owl (Otus scops). We assessed how parents allocated food during the night in relation to a manipulation of ultraviolet (UV) reflectance of the cere (skin above the beak) of their offspring. Reflectance of the cere shows a marked peak in the UV part of the spectrum, and location of the UV peak is related to nestling body mass (i.e. heavier nestlings have a UV peak at lower wavelengths). We found evidence of parental bias in favour of lighter offspring: UV-reduced nestlings gained more weight during the night than their control siblings. This study provides the first experimental evidence of the use of visual cues for parent–offspring communication in a nocturnal bird.

Spotless starlings rely on public information while visiting conspecific nests: an experiment

Animals may acquire information on potential breeding sites by prospecting, which allows future optimal selection of breeding territories. The reproductive success of conspecifics, as public information (PI), has been proposed as one of the cues that prospectors could gather and then use for future reproductive decisions. We experimentally decreased brood size in spotless starling nests to investigate whether this species gathers PI while visiting conspecific nests. We expected visiting frequency to decline with the experimental decrease in brood size because visitors are expected to prefer sites with high reproductive success and to spend more time at those sites to gain familiarity. Furthermore, the effect of the experimental manipulation was recorded at three different stages of the nestling period to establish the importance of the reliability of PI. Brood size decreased in direct relation to the manipulation and, consequently, parental feeding rates decreased too. Visiting frequency of starlings to conspecific nests was affected by the interaction between the experimental manipulation and the stage in the nestling period: visiting frequency increased from decreased to control nests at the end of the nestling period, not so strongly in the middle of that period and it was not affected by the manipulation at the beginning of it. This variation in visiting frequency seemed to be better explained by brood size than by parental provisioning rate. These results may be interpreted as spotless starlings visiting conspecific nests to gather PI, which seems to increase its informative value when its reliability does.

Natural Cross Chlamydial Infection between Livestock and Free-Living Bird Species

The study of cross-species pathogen transmission is essential to understanding the epizootiology and epidemiology of infectious diseases. Avian chlamydiosis is a zoonotic disease whose effects have been mainly investigated in humans, poultry and pet birds. It has been suggested that wild bird species play an important role as reservoirs for this disease. During a comparative health status survey in common (Falco tinnunculus) and lesser (Falco naumanni) kestrel populations in Spain, acute gammapathies were detected. We investigated whether gammapathies were associated with Chlamydiaceae infections. We recorded the prevalence of different Chlamydiaceae species in nestlings of both kestrel species in three different study areas. Chlamydophila psittaci serovar I (or Chlamydophila abortus), an ovine pathogen causing late-term abortions, was isolated from all the nestlings of both kestrel species in one of the three studied areas, a location with extensive ovine livestock enzootic of this atypical bacteria and where gammapathies were recorded. Serovar and genetic cluster analysis of the kestrel isolates from this area showed serovars A and C and the genetic cluster 1 and were different than those isolated from the other two areas. The serovar I in this area was also isolated from sheep abortions, sheep faeces, sheep stable dust, nest dust of both kestrel species, carrion beetles (Silphidae) and Orthoptera. This fact was not observed in other areas. In addition, we found kestrels to be infected by Chlamydia suis and Chlamydia muridarum, the first time these have been detected in birds. Our study evidences a pathogen transmission from ruminants to birds, highlighting the importance of this potential and unexplored mechanism of infection in an ecological context. On the other hand, it is reported a pathogen transmission from livestock to wildlife, revealing new and scarcely investigated anthropogenic threats for wild and endangered species.

Do great tits rely on inadvertent social information from blue tits? A habitat selection experiment

Sympatric species sharing requirements are competitors, but recent evidence suggests that heterospecifics may also be used as a source of information. The heterospecific habitat copying hypothesis proposes that individuals of one species might use information inadvertently produced by the breeding performance of individuals of other species to assess habitat quality whenever the two species share needs. In this study, we provide the first experimental test of this hypothesis by examining whether the manipulated reproductive success of blue tits (Cyanistes caeruleus) is used as heterospecific inadvertent social information (ISI) in breeding-habitat selection by sympatric great tits (Parus major). The reproductive success of blue tits was manipulated 1year at the scale of patches by transferring nestlings from decreased to increased patches. No evidence was found of great tits using the reproductive success of blue tits as a source of heterospecific ISI. However, dispersal decisions by adult great tits correlated with information on con- and heterospecific densities, which constitute other sources of ISI. As density and breeding performance are tightly intertwined forms of information, the difficulty in distinguishing between them might lead great tits to use heterospecific ISI more in the form of density than breeding performance when making dispersal decisions.

Informative content of multiple plumage-coloured traits in female and male European Rollers

Animals may assess the quality of other individuals by using information that different ornaments may provide. The European Roller (Coracias garrulus) is a socially monogamous species in which males and females display highly conspicuous plumage colouration. According to the mutual selection hypothesis, we predicted that, in this species, plumage coloration could signal individual quality in both sexes because both female and male rollers invest a considerable amount of time caring for their offspring. We used spectrophotometric measurements to investigate the information content of multiple plumage colour traits. We found that the roller is actually a sexually dimorphic and dichromatic species. Different plumage colours from different origins were correlated within individual. Head and back brightness correlated with body condition in both sexes, and in males, head brightness correlated with the number of fledglings in successful nests, while head green-yellow saturation correlated with parental provisioning. Meanwhile, in females, back brightness was related to the number of fledglings in successful nests and to parental provisioning rate. In addition, there was a positive assortative mating in relation to weight, body condition, head green-yellow saturation and back brightness. Finally, we found a positive correlation between parent and offspring coloration. Altogether, these results suggest that multiple colour traits may act as quality indicators in the roller and that they may be used by the two sexes to assess potential mate quality.

Parental favouritism strategies in the asynchronously hatching European Roller ( Coracias garrulus )

In altricial birds, resource allocation during early developmental stages is the result of an interaction between parental feeding decisions and scramble competition between nestmates. Hatching asynchrony in birds leads to a pronounced age hierarchy among their offspring. Therefore, whenever parents exert control over resource allocation parents feeding asynchronous broods should simultaneously assess individual offspring internal condition and age. In this study, we first studied whether the highly ultraviolet (UV) reflective body skin of nestlings in the asynchronous European Roller (Coracias garrulus; roller hereafter) relates to nestling quality. In a second stage, we experimentally studied parental biases in food allocation towards senior and junior sibling rollers in relation to a manipulation of UV reflectance of the skin of their offspring. Heavier roller nestlings had less brilliant and less UV saturated skins than weaker nestlings. In our experiment, we found that parents with large broods preferentially fed nestlings presenting skin coloration revealing small body size (i.e. control nestlings) over nestlings presenting skin coloration revealing large body size (i.e. UV-blocked nestlings). Within the brood, we found that parental food allocation strategy depended on nestling age: parents preferentially fed senior nestlings signalling small body size, but did not show preference between control and UV-blocked junior nestlings. These results emphasise that parent rollers use UV cues of offspring quality while balancing the age of their offspring to adjust their feeding strategies, and suggest that parents may adopt finely tuned strategies of control over resource allocation in asynchronous broods.

Host personalities and the evolution of behavioural adaptations in brood parasitic–host systems

Animals show consistent individual variation in behaviour over time and across different situations, a phenomenon commonly termed personality. Personality studies are important because, if personality traits extend their influence across a wide range of situations, they may help to explain the paradoxical occurrence of nonoptimal behaviours. A paradigmatic example of nonoptimal behaviour is the striking lack of behavioural defences of some hosts of obligate avian brood parasites despite the evident costs they incur. Here we propose that the interplay between personality features expressed by hosts outside the nest and the specialized behaviours expressed by hosts in/or near the nests to deter avian brood parasites (i.e. nest defence, egg and nestling recognition and ejection) may affect the average level of host behavioural defences exhibited at the population level as well as the evolutionary dynamics of brood parasite–host interactions. Differences in personality between hosts may relate to the observed variation in susceptibility to brood parasitism in a given population, as well as to the set of host defensive behaviours expressed in/or near the nests to prevent the costs of brood parasites. In addition, differences in parasite density might have different consequences for the fitness of different personality traits and might potentially explain intermediate tolerance to parasitism and even acceptance of parasitic eggs by hosts in populations exposed to low selection pressures by brood parasites. Future research should thus aim to identify how the different personality traits may relate to specialized host defences to explain the occurrence of apparent maladaptive host behaviours.