Raphael Igor Dias

Effects of position and flock size on vigilance and foraging behaviour of the scaled dove Columbina squammata

Amongst the benefits of foraging in flocks are the enhancement of food finding and predation avoidance. Characteristics such as size, individual position, as well as position and distance between members are factors that may influence vigilance and foraging. In a study using scaled doves, Columbina squammata, I observed a negative correlation between group size and vigilance and a positive correlation with time spent foraging, which suggests a reduction of costs and an increase of benefits as a consequence of larger group sizes. Individual position in the flock appeared to be an important factor in this trade-off. Peripheral individuals were more vigilant and foraged less than central ones, suggesting an edge effect in flocks of this species. The clustering of conspecifics may be related with fast transmission of information. Overall, aggressive interactions were rarely observed; when registered, they occurred mostly in larger groups, suggesting an effect of interference competition. These results imply that predation may be a strong pressure on the scaled doves flock formation and behaviour.

Cooperative Breeding in the Campo Flicker I: Breeding Ecology and Social Behavior

Abstract. Cooperative breeding and complex social systems are known in woodpeckers, but most available information concerns species of the North Temperate Zone. The social behavior and breeding ecology of tropical woodpeckers are poorly documented. Here we present data on the breeding behavior and ecology of a tropical woodpecker, the Campo Flicker (Colaptes campestris campestris). We confirm for the first time, through behavioral observations, facultative cooperative breeding in this species. Both males and females were observed visiting the nest during the incubation and nestling period. In cooperative groups some helpers were identified as young from the previous year, but others seem to be unrelated individuals that joined the groups. In addition, our behavioral observations strongly suggest both polygyny (a male breeding with more than one female simultaneously) and joint nesting (multiple females contributing eggs to a single nest) in some but not all cooperative groups. These observations reveal a complex social system in this tropical species, with high potential for reproductive conflicts both within and among groups, due to the presence of new potential breeders or through advantages emerging from the effects of group size.

TERRITORIAL CLUSTERING IN THE BLUE-BLACK GRASSQUIT: REPRODUCTIVE STRATEGY IN RESPONSE TO HABITAT AND FOOD REQUIREMENTS?

Abstract. A phenomenon currently not well understood is the reproduction of some species in clustered territories. We evaluated two ecological hypotheses (material-resources and predation hypotheses) that could explain cluster formation during reproduction of the Blue-black Grassquit (Volatinia jacarina), a socially monogamous bird with a high rate of extra-pair fertilization. Additionally, we considered the breeding synchrony of females, since synchronization may serve as a means of diluting predation. To this end, we compared the breeding synchrony of females in clusters to that of those in solitary territories. We found support for the material-resources hypothesis in terms of vegetation structure and food availability: territories were clustered in habitat with more food and a more complex vegetation structure. Breeding synchrony of females in clusters was higher than that of females in solitary territories, but probably not as a mechanism to dilute predation: pairs within clusters suffered lower reproductive success because of elevated predation. The advantages gained by reproducing in clusters in areas of more complex vegetation structure and more food may offset the disadvantages due to predation, especially over a longer temporal scale. Our results suggest that the aggregation of Blue-black Grassquit territories could be explained by habitat heterogeneity in terms of vegetation and food, but these results do not exclude other hypotheses related to sexual selection and/or competition leading to aggregation.

Conspicuous sexual signals in a socially monogamous passerine: the case of neotropical Blue-black Grassquits

Sexual selection has shaped many traits involving communication, behavior, morphology, and reproductive strategies. Sexual communication in the Blue-black Grassquit Volatinia jacarina involves an iridescent, nuptial plumage and the exhibition of a complex motor and acoustic mating display. Blue-black Grassquits breed in small, aggregated territories, are socially monogamous, but have high rates of extrapair fertilization and intensive paternal care. Here, we discuss the evolution of sexually selected ornaments in this species and review some studies that have evaluated their costs and benefits. Our data suggest that females have an active role in obtaining extrapair fertilizations, but appear to be indiscriminate in their choice of extrapair males. However, it remains necessary to evaluate female choice in natural circumstances, and the effects of such on male reproductive success. This is particularly important because, in the field, we found that the male motor display may provide a useful cue for nest predators, and therefore evolution of female choice may be constrained by the probability of higher nest predation associated with choosing males exhibiting high display rates. Our studies also indicate that small males have an advantage in aggressive interactions with larger males. We hypothesize that small male size may be driven by female choice for male motor performance, including aspects of display agility and acrobatic capacity, leading to better performance by small males in intrasexual interactions involving flight within confined spaces. Alternatively, the food resource may be more valuable to smaller males, resulting in higher aggression to access the food.

Helping enhances productivity in campo flicker (Colaptes campestris) cooperative groups

Reproductive adults in many bird species are assisted by non-breeding auxiliary helpers at the nest, yet the impact of auxiliaries on reproduction is variable and not always obvious. In this study, we tested Hamilton’s rule and evaluated the effect of auxiliaries on productivity in the facultative cooperative breeder campo flicker (Colaptes campestris campestris). Campo flickers have a variable mating system, with some groups having auxiliaries and others lacking them (i.e., unassisted pairs). Most auxiliaries are closely related to the breeding pair (primary auxiliaries), but some auxiliaries (secondary auxiliaries) are unrelated females that joined established groups. We found no effect of breeder quality (body condition) or territory quality (food availability) on group productivity, but the presence of auxiliaries increased the number of fledglings produced relative to unassisted pairs. Nonetheless, the indirect benefit of helping was small and did not outweigh the costs of delayed breeding and so seemed insufficient to explain the evolution of cooperative breeding in campo flickers. We concluded that some ecological constraints must limit dispersal or independent breeding, making staying in the group a “best-of-a-bad-job” situation for auxiliaries.

Cooperative Breeding in the Campo Flicker II: Patterns of Reproduction and Kinship

Abstract. Understanding the evolution of cooperative breeding systems remains a central issue in evolutionary biology. In this context, molecular tools have contributed greatly toward understanding kinship patterns within groups and resolving long-standing issues regarding mating systems and parentage. We used such molecular tools to examine patterns of kinship in the Campo Flicker (Colaptes campestris campestris), a facultative cooperative breeder, to answer questions concerning its mating system and patterns of reproductive skew. Genetic analysis revealed that the species is predominantly monogamous in both cooperative groups and socially monogamous pairs, but in several cooperative groups auxiliary females contributed eggs to the nest. In contrast, within groups direct reproduction by auxiliary males was rare. We observed no cases of extra-group paternity but detected cases of quasi-parasitism in socially monogamous pairs. Levels of relatedness within groups were high; auxiliaries of both sexes were often offspring or siblings of the primary breeding pair but were sometimes unrelated to the breeding pair. The structural genetic complexity of groups and high intragroup relatedness generate a social system in which cooperation among group members coexists with competition for opportunities to breed.

Nestling use of alternative acoustic antipredator responses is related to immune condition and social context

Birds present a variety of antipredator responses, including the use of acoustic signals that may be directed to other individuals or to the predator. We tested competing hypotheses regarding antipredator responses by analysing patterns of variation in the use of distress calls in campo flicker, Colaptes campestris campestris, nestlings. More specifically, we tested whether immune response and social context (presence or absence of other individuals of the social group) were associated with variation in use of acoustic signals in response to human handling. Individuals with higher immunocompetence used proportionally more harsh, low-pitched calls (‘scream’ notes) than individuals with lower immunocompetence, while the latter used mostly tonal, high-pitched calls (‘week’ notes); in both cases there was no influence of the social context on call type. Individuals responded to the social context by giving fewer scream notes and week notes in the presence of adults of the social group than when the adults were absent. Although playbacks are necessary to determine the function of the calls, our results indicate that campo flicker nestling antipredator calls could be used to attract other individuals of the group to help defend the nestling. Also, the use of proportionally more scream notes by healthier individuals suggests that these notes could act as an honest signal of the nestlings’ physiological condition.

Nesting biology of the Yellow-faced Parrot (Alipiopsitta xanthops), a species without nest-site fidelity: an indication of high cavity availability?

Abstract Parrots are considered a globally threatened group but, despite that, little is known about the ecology, reproduction and behaviour of many species in the wild, especially those of dry tropical habitats. I studied the breeding biology of the Yellow-faced Parrot (Alipiopsitta xanthops) between 2007 and 2009. Yellow-faced Parrots are endemic to the Cerrado (neotropical savanna) biome of central South America. Their reproductive biology is poorly known and here I provide basic information on reproduction, including breeding success, nest-site characteristics, and whether the availability of cavities is a limiting factor. Average clutch-size was two eggs, and hatching success was high (92%). All nests were in cavities in termite mounds, with used cavities deeper and with wider entrances than cavities that were not used. Entrances to nests were orientated towards the north-east. Although the number of cavities in the environment appears to be high, specific nesting requirements and competition with other cavity-nesting birds and insects may reduce the number of cavities that can be used. Nevertheless, nests were never observed to be reused and site-fidelity appeared to be low. Specific nesting requirements and low site-fidelity may create problems for near-threatened species with declining populations, such as the Yellow-faced Parrot. Additional studies and the immediate implementation of conservation actions are essential to avoid future declines of populations of Yellow-faced Parrots.

Parental and alloparental investment in campo flickers (Colaptes campestris campestris): when relatedness comes first

In cooperative species, parental investment may be shared with auxiliaries. Kin selection and other types of benefits have been proposed to explain the evolution of helping behavior. Auxiliaries are expected to be more helpful when closely related to the breeders. In this context, breeders may adjust parental investment in at least three ways: (a) reducing their effort and being compensated by the auxiliaries’ investment (compensatory effect); (b) maintaining their effort, with an increase in total investment (additive effect); or (c) partial compensation, i.e., a decrease in care by the parents but not by as much as the increase in care from the auxiliaries. We studied the cooperative species Colaptes campestris campestris and tested the following hypotheses: (1) partial compensation effect occurs, (2) parents modulate their investment relative to the auxiliaries’ investment, (3) auxiliaries adjust their investment according to their relationship to the offspring, and (4) groups whose members are in better physical condition fledge more young or these are in better condition. We determined relatedness within groups and monitored parental and alloparental behavior during breeding. Breeders in cooperative groups presented the same investment as unattended breeders. Restricting the analysis to cooperative groups revealed that the investment made by auxiliaries reflected their relatedness to the young and positively affected the investment by breeders. Results suggest that a partial compensation occurs in the species, with breeders reducing their effort despite the small increase in overall nest investment. Results highlight the importance of kin selection in the evolution of cooperative breeding in campo flickers.Significance statementCooperatively breeding birds may have auxiliaries that help rear their brood. The evolution of helping behavior may derive from kin selection, where auxiliaries could gain a genetic benefit by helping to rear kin, which occurs when groups are composed of closely related individuals. However, it is often the case that some offspring may not be closely related to the auxiliaries due to the species’ mating system. We used the cooperatively breeding campo flickers to investigate whether and how the presence of auxiliaries might affect parental care patterns and nest productivity. We found that breeders did not reduce their investment in the presence of auxiliaries and that cooperative groups present the same overall investment when compared with unassisted pairs, indicating that the investment made by auxiliaries was not large enough to affect the total investment nor the breeders’ investment. Our results also show that auxiliaries increased their investment when they were more closely related to the brood.