Abstract: Male fowl (Gallus gallus) that have recently mated invest in their mates by producing antipredator alarm signals at a higher rate. It remains unclear, however, whether these males are investing judiciously in their mates, or responding more generally to recent mating success. Here, we manipulated each male's mating experience with two different females to test whether males invest selectively in their mates. For 1 wk, males could interact with both females, but could mate with only one of them. In the second week, we removed either the mated or the unmated female and measured the male's rate of alarm calling. Males did not invest preferentially in their mates, suggesting that increased alarm calling is a more general response to recent mating experience. This relationship could be based on a relatively simple cognitive rule of thumb or on an underlying physiological mechanism. Testosterone and corticosterone are associated with reproduction and antipredator behaviour in other species and so could provide the necessary physiological link in fowl. To test this, we measured plasma levels of testosterone and corticosterone before, during and after mating. Results show that hormone levels did not change as a function of male mating status and hence cannot provide the link between mating and calling behaviour. Instead, we suggest that a general cognitive mechanism is more likely to explain prudent mate investment in this species.
Abstract: Bell miner (Manorina melanophrys) colonies are closely associated with decreased avian abundance and diversity and an apparently associated increase in psyllid abundance. However, a causative link between the presence of bell miners and increased psyllid abundance has yet to be established. We took advantage of the movement of bell miners into two new areas to investigate the ecological consequences of bell miner occupation on both avian and psyllid abundance. We monitored the number of bell miners and other avian species, using area searches, and psyllid abundance by monthly counts of lerp on leaves. Bell miner presence alone had limited effect on either bird diversity or abundance. However, when miners were also giving their distinctive ‘tink’ vocalisation, a significant decrease in avian abundance and diversity was observed. This evidence supports the hypothesis that ‘tink’ vocalisations are used by interspecific competitors to detect bell miner colonies. At the time of initial occupation, new sites did not have significantly elevated levels of psyllids compared with surrounding areas unoccupied by bell miners. Six months later one of the two newly occupied sites had significantly more Cardiaspina spp. than either the long-established colony or an unoccupied control site. In contrast, infestations of Glycaspis spp. remained significantly lower at both new sites when compared with the long-established colony, but equivalent to unoccupied areas. Given this, we conclude that bell miner occupation does not necessarily lead to an increase in psyllid abundance, characteristic of tree dieback in some colonies, and that a causative link between bell miner presence and declining tree health remains to be demonstrated.
Abstract: Research on cooperative breeding has begun to focus on direct fitness benefits gained by helpers, particularly when individuals are unrelated to those they assist. There has been considerable interest in helping possibly operating as a signal, either to show off individual quality to potential mates (‘social prestige’) or to ensure group membership (‘pay to stay’). However, empirical investigation of these phenomena remains sparse. Here we investigate the potential for signalling via provisioning behaviour in the bell miner, Manorina melanophrys, an obligate cooperative breeding species in which the predominantly male helpers are commonly unrelated to breeders. Aggression between birds was extremely rare, and there was little to indicate a pay to stay system. The presence versus absence of members of the breeding pair as a potential audience at the nest had little influence on helper behaviour (e.g. load size/composition, visit duration or frequency). Helpers did produce more individually distinctive vocalizations when in the presence of another helper or the breeding male, although presence of the breeding female (a likely target of male signals) surprisingly had no effect. There was also evidence that nest arrival times coincided somewhat. These results are probably best explained by the helpers and breeding males being involved in additional cooperative behaviours when away from the nest, such as mobbing. Overall, there does not appear to be any evidence that bell miner helpers use nestling provisioning to signal their quality and/or work rate to one another or to either member of the breeding pair.
Abstract: Cooperatively breeding bell miners (Manorina melanophrys) have numerous male helpers assisting at multiple nests. Helpers are often related to the brood they aid, consistent with kin selection. However, there are also unrelated helpers for which other direct fitness benefits are likely to accrue. Bell miner nestlings can become infested by the larvae of a parasitic fly (Passeromyia indecora), which reduce growth and can be fatal. We investigated the amount of time that breeding pairs and helpers closely inspected nests and preened nestlings, behaviors apparently directed at detecting and removing parasites, a form of helping previously unstudied in a cooperative bird. Female breeders provided the greatest antiparasite effort, with breeding males and helpers not differing in effort regardless of their relatedness to the breeding female or brood. We also experimentally infested nests with nonparasitic flies and larvae. All individuals removed the introduced "parasites" if and when they encountered them. Compared with control sessions, inspection effort increased for all birds immediately after the experimental infestations, but only for a short, 5-min period. Further, we detected no changes in helper antiparasite behaviors after the temporary experimental removal of either breeding females or males. Such consistent helping behavior, independent of relatedness and potential audience effects, suggests that antiparasite behavior in bell miners is not particularly kin directed or operating as a signal of helper quality. Our results instead suggest that helper antiparasite effort appears to represent adaptive investment in the welfare of the brood, consistent with direct fitness benefits from group augmentation.
Abstract: Acoustically-mediated individual discrimination has been the focus of much investigation in ornithology. For cooperatively breeding species, strong selection pressure favouring individual recognition during acts of altruism is predicted under many of the most interesting hypotheses proposed to account for helping behaviour. We investigated differences in 157 calls given by 12 different individuals as they provisioned nestlings, including both breeding and helper bell miners Manorina melanophrys (Meliphagidae), a cooperatively breeding honeyeater endemic to south-eastern Australia. Individual differences were apparent in all 15 call parameters analysed, many with a high level of repeatability. Moreover, the information capacity of mew calls allows as many as 515 different signatures to exist in the system. As many parameters showed strong sex differences, separate discriminant functions were used to predict individual identity within each sex. Five parameters were used in a function that correctly identified over 90% of female calls in both a training (n=35) and test dataset (n=11) not used to generate the function. Among males, a separate function used six parameters to correctly assign individual identity in 89.3% (n=84; training) and 77.8% (n=27; test) of cases. Three original parameters, including spectral and spatial characteristics, were highly correlated with functions predicting identity in both sexes. The accuracy of functions was not influenced by a signaller's sex, breeding status, or by sampling period which was spread over as much as two breeding seasons within individuals. Significant potential therefore exists for bell miners to use these simple provisioning calls in individual discrimination. If this is the case, call information also has the potential to be used by receivers as predicted by signalling hypotheses proposed to account for cooperative helping behaviour, such as the pay-to-stay and social prestige hypotheses.
Abstract: We studied a population of rufous whistlers, Pachycephala rufiventris, throughout a single breeding season in central New South Wales, Australia. We evaluated the relation between plasma testosterone m and reproductive behaviors using both simulated territorial intrusions (STls) and subcutaneous T implants. We compared circulating T values to aggression levels of males xD; (using STI) during pair bond and territory establishment and again during incubation. Although plasma T levels were significantly lower in the latter period, male responsiveness to STI, in terms of proximity to decoy, call rate, and number of attacks on the decoy, was indistinguishable between the two breeding stages. T levels of males exposed to STI were not different from the levels of unexposed free-living males at the same breeding stage. The xD;effect of exogenous T on parental behavior was examined by comparing duration of incubation bouts of males and their mates prior to and after T treatment. T males significantly reduced the amount of time they incubated following implantation, whereas Control males maintained their incubation effort. After cessation of breeding activities, T males displayed significantly higher call rates due to increased use of the primary intersexual advertisement call in this species. The reduction of incubation behavior following T implantation emphasises the functional significance of the rapid decline in T in free-living males during incubation. The results from both experiments suggest that intersexual advertisement, rather than territorial aggression, may be dependent on high T levels in this species.
Abstract: The function of vocalisations and aggressive behaviours observed in a free-living population of Rufous Whistlers, Pachycephala rufiventris, was studied throughout a breeding season in central western New South Wales. Individuals of the population were colour banded and the behaviour of adult males observed and quantified for 10-min periods during discrete stages of the breeding cycle. The population was found to be totally migratory or nomadic at this site; adult males participated in all breeding activities except nest construction. Two new courtship displays are described and six distinct call types were identified and recorded. Total call tares reached a peak during nest construction, before gradually falling to very low rates by the cessation of breeding activities. On the basis of extensive field observations it was concluded that this species uses calls for both territorial definition and intersexual attraction. While some calls were more frequently associated with a territorial or intersexual function, none of the six calls was used exclusively fur either. Aggressive behaviour was quantified and was most prevalent early in the breeding season when territories and pair bonds were being established. Mate-guarding, in the form of periods that males spent within 5 m of the female, was most common during nest construction when females were fertile.
