Nathalie Seddon

ECOLOGICAL ADAPTATION AND SPECIES RECOGNITION DRIVES VOCAL EVOLUTION IN NEOTROPICAL SUBOSCINE BIRDS

Abstract Given that evolutionary divergence in mating signals leads to reproductive isolation in numerous animal taxa, understanding what drives signal divergence is fundamental to our understanding of speciation. Mating signals are thought to diverge via several processes, including (1) as a by‐product of morphological adaptation, (2) through direct adaptation to the signaling environment, or (3) to facilitate species recognition. According to the first two hypotheses, birdsongs diversify in different foraging niches and habitats as a product of selection for optimal morphology and efficient sound transmission, respectively. According to the third hypothesis, they diversify as a result of selection against maladaptive hybridization. In this study I test all three hypotheses by examining the influence of morphology, acoustic environment, and the presence of closely related congeners on song structure in 163 species of antbird (Thamnophilidae). Unlike oscine passerines, these Neotropical suboscines make ideal subjects because they develop their songs without learning. In other words, patterns of vocal divergence are not complicated by cultural evolution. In support of the morphological adaptation hypothesis, body mass correlates with the acoustic frequency of songs, and bill size with temporal patterning. These relationships were robust, even when controlling for phylogenetic inertia using independent contrasts, suggesting that there has been correlated evolution between morphological and acoustic traits. The results also support the acoustic adaptation hypothesis: birds which habitually sing in the understory and canopy produce higher‐pitched songs than those that sing in the midstory, suggesting that song structure is related to the sound transmission properties of different habitat strata. Finally, the songs of sympatric pairs of closely related species are more divergent than those of allopatric pairs, as predicted by the species recognition hypothesis. To my knowledge, these data provide the first direct evidence that species recognition and ecological adaptation operate in tandem, and that the interplay between these factors drives the evolution of mating signals in suboscine birds.

Male heterozygosity predicts territory size, song structure and reproductive success in a cooperatively breeding bird

Recent studies of non–social animals have shown that sexually selected traits signal at least one measure of genetic quality: heterozygosity. To determine whether similar cues reveal group quality in more complex social systems, we examined the relationship between territory size, song structure and heterozygosity in the subdesert mesite (Monias benschi), a group–living bird endemic to Madagascar. Using nine polymorphic microsatellite loci, we found that heterozygosity predicted both the size of territories and the structure of songs used to defend them: more heterozygous groups had larger territories, and more heterozygous males used longer, lower–pitched trills in their songs. Heterozygosity was linked to territory size and song structure in males, but not in females, implying that these traits are sexually selected by female choice and/or male–male competition. To our knowledge, this study provides the first direct evidence in any animal that territory size is related to genetic diversity. We also found a positive association between seasonal reproductive success and heterozygosity, suggesting that this heritable characteristic is a reliable indicator of group quality and fitness. Given that heterozygosity predicts song structure in males, and can therefore be determined by listening to acoustic cues, we identify a mechanism by which social animals may assess rival groups, prospective partners and group mates, information of potential importance in guiding decisions related to conflict, breeding and dispersal.

The structure, context and possible functions of solos, duets and choruses in the subdesert mesite (Monias benschi)

Subdesert mesites produced five distinct types of vocal element which they combined to produce two broad classes of song syllable. One of these syllables was exclusive to males and the other was mainly given by females. Song syllables were either produced in series by single individuals to give solo songs, or 2-5 five birds vocalised simultaneously with varying degrees of temporal precision to give duets and choruses. Pair-duets were the most common and male solos the least common form of song recorded. Females initiated and terminated significantly more songs than males and male syllables followed female syllables more promptly than the converse. However, the syllable structure of male and female solos changed when synchronised to form pair-duets indicating that, in contrast to most previous studies of duetting species, these songs are a function of both male and female behaviour. Only a subset of each group contributed to duets and choruses and participation was positively correlated with mass for males and females both within and across groups. Song activity remained at a low but relatively constant rate throughout both the day and season. The wide variety of contexts in which songs were produced indicated that they serve multiple functions: some appear to be cooperative endeavours (e.g. to maintain contact in dense vegetation and to defend territories), others may be underpinned by conflicts and could function in matedefence or in inter- and intra-sexual assessment within groups.

VOCAL COMMUNICATION IN THE PALE-WINGED TRUMPETER (PSOPHIA LEUCOPTERA): REPERTOIRE, CONTEXT AND FUNCTIONAL REFERENCE

Adult pale-winged trumpeters produce a varied repertoire of vocalizations: apart from one loud tremolo song we recorded 11 structurally discrete close-range calls, one of which (the mew) was individually distinct. There was significant variation across vocalization type with respect to the identity and behaviour of the caller and the response of the receiver(s). It was possible to group vocalizations into six broad contextual classes: alarm, recruitment, social, contact, feeding and territory defence. On detection of danger, trumpeters gave two acoustically different calls, one for aerial predators, and another for terrestrial predators or conspecific intruders. They also produced distinct calls on detection of large prey items such as snakes. These (alarm and snake-finding) call types seemed to evoke different responses by receivers and therefore appeared to be functionally referent. Vocal behaviour was positively correlated with dominance rank and at least two other calls had important roles in mediating social interactions within the group. Finally, the mew call was only given when a trumpeter was separated from, and usually out of visual contact with the rest of the group. This call was functionally referent, eliciting a vocal response from receivers: they produced a loud grunt call, which was also unique to this situation. This is the first experimental demonstration in a bird of the proximate factors motivating production of an individually distinct contact call.

Duetting in the subdesert mesite Monias benschi: evidence for acoustic mate defence?

Abstract. Despite numerous hypotheses proposed for the function of duets, there is currently no consensus as to why males and females should coordinate their songs in such a precise way. There is evidence indicating that duets sometimes serve in territory defence, but additional functions are rarely considered. The mate-defence hypothesis proposes that birds sing in response to their partners song and the resulting duet repels rivals and may prevent desertion of a partner. We investigated this idea in the subdesert mesite Monias benschi using playback experiments in which we broadcast recordings of solos and duets to single birds and groups. Two predictions of the hypothesis were met: (1) the solo songs of both sexes incited aggressive responses from paired birds of the same sex; and (2) compared to solo songs, pair duets elicited weaker responses from groups and duetting pairs. However, groups responded to male duets with a vigour equal to that with which they responded to male solos. This indicated that the weaker responses of groups to pair duets compared to male solos was a function of the sex rather than number of vocalising birds. Groups responded more strongly to male solos than to either female solos or pair duets, and females responses were generally weaker than those of males. This may reflect stronger competition among males for mates, due to a male-biased sex ratio in the population. We conclude that song serves similar functions in each sex and that duets may arise through mutual mate defence.

Estimating population size in the subdesert mesite (Monias benschi): new methods and implications for conservation

Abstract The subdesert mesite, a terrestrial non-passerine bird endemic to the Mikea Forest of southwest Madagascar, is currently classified as globally threatened (category: Vulnerable). However, accurate assessment of threat in accordance with the IUCN Red List criteria (A, B and C) requires data on effective population size, area of habitat occupied and rate of decline, none of which is available for this species. Here we present the first empirical estimates of its population size using five complementary methods, three incorporating data on territory size and two using data gathered during call-playback surveys conducted throughout its entire global range. Estimates vary from 98,000 to 152,000 individuals, with the most reliable possibly being that generated by distance sampling (115,000). This figure is more than an order of magnitude greater than the only published estimate of

Yelling for sex : harem males compete for female access in bronze-winged jacanas

Sperm competition in sex-role reversed, polyandrous jacanas is intense because females copulate with multiple male mates before laying each clutch. These males may be unable to attempt to maximize their share of copulations by mate guarding or forcing copulations. Instead, males in polyandrous harems may compete for sexual access to the female by giving a call, termed the yell, to attract her. Male bronze-winged jacanas, Metopidius indicus, yelled at higher rates in larger harems, and when the female was further from the yeller or on a comates territory. Half of all yells were given at mating platforms where all copulations occurred. Males that received the clutch yelled at lower rates during the incubation and chick care periods. Yells attracted the female when she was far from the yeller or with a comate. When the yell of a polyandrous male was broadcast from his territory, the female was more likely to fly to his territory during playback than during control periods. Within polyandrous harems the males that yelled at the highest rates received the most copulations, and three out of four females gave clutches to the male that gave the longest and most frequent yells, so females may have used yells to assess male quality. Intrusions by females, but not males, increased during yell playbacks, and tended to be more frequent on the territories of males with high yell rates. Females may therefore respond to their mates yells because yells may attract female intruders which may attempt to take over the territory. Copyright 1999 The Association for the Study of Animal Behaviour.

Mating system, philopatry and patterns of kinship in the cooperatively breeding subdesert mesite Monias benschi

In the first molecular study of a member of the threatened avian family, Mesitornithidae, we used nine polymorphic microsatellite loci to elucidate parentage, patterns of within‐group kinship and occurrence of extra‐group paternity in the subdesert mesite Monias benschi, of southwest Madagascar. We found this cooperatively breeding species to have a very fluid mating system. There was evidence of genetic monogamy and polygynandry: of the nine groups with multiple offspring, six contained one breeding pair with unrelated helpers and three contained multiple male and female breeders with related helpers. Although patterns of within‐group kinship varied, there was a strong positive relationship between group size and relatedness, suggesting that groups form by natal philopatry. There was also a strong positive correlation between within‐sex and between‐sex relatedness, indicating that unlike most cooperatively breeding birds, philopatry involved both sexes. In contrast to predictions of kin selection and reproductive skew models, all monogamous groups contained unrelated individuals, while two of the three polygynandrous groups were families. Moreover, although between‐group variation in seasonal reproductive success was related to within‐group female relatedness, relatedness among males and between the sexes had no bearing on a groups reproductive output. While kin selection may underlie helping behaviour in females, factors such as direct long‐term fitness benefits of group living probably determine helping in males. Of the 14 offspring produced by fully sampled groups, at least two were sired by males from neighbouring groups: one by a breeding male and one by a nonbreeding male, suggesting that males may augment their reproductive success through extra‐group paternity.

The importance of the Nilo and Nguu North Forest Reserves for the conservation of montane forest birds in Tanzania

In July to October 1995 we conducted bird surveys in two forest reserves (FRs) in Tanzania: Nilo FR in the East Usambara Mountains and Nguu North FR in the Nguu Mountains. The survey results were used to assess the importance of the two FRs for the conservation of threatened, near-threatened and restricted range montane bird species, and threats to the forest in these areas were identified. The conservation importance of the East Usambaras and the Nguus relative to other forested mountain ranges in Tanzania was assessed. It was found that Nilo FR and the adjacent forested public land is an important site for the conservation of Usambara weaver and long-billed tailorbird, and Nguu North FR for east coast akalat. Both FRs harbour other forest-dependent species of conservation interest whose survival prospects would be enhanced by improved protection of the reserves. Both FRs are subject to degradation, predominantly through pit-sawing and cultivation. There is an urgent need for a long-term conservation programme in these FRs and we make practical recommendations for their future management.

Population size and habitat associations of the Long-tailed Ground-roller Uratelornis chimaera

The Long-tailed Ground-roller ( Uratelornis chimaera ) is a globally Vulnerable, restricted-range species of dry forests in south-west Madagascar. We studied a population in 1997–2000, finding that nest-building was relatively synchronous and that pairs preferentially nested next to open areas, such as driveable tracks. By searching for trackside nests and for footprints, we conducted surveys throughout the known range of the species. Total transect coverage was 153 km, along which we encountered a minimum of 28 breeding pairs. By dividing the transects into 41 randomly distributed survey strips, each 1.2 km in length and 200 m broad, we intensively sampled an area of 9.84 km 2 . Using transect data, we made a tentative estimate of 5.7 mature adults km −2 , from which we estimated a global population of 21,092 individuals, based on our calculation from satellite imagery that 3,706 km 2 of suitable habitat remained. By comparing habitat data at points with and without ground-rollers we found that, contrary to previous statements, they prefer lower stature or degraded habitats, and have no direct association with the endemic cactus-like tree Didierea madagascariensis . We used a novel census technique to provide the first quantitative data on population size, population density, breeding behaviour and ecology in the Long-tailed Ground-roller, or any member of the family Brachypteraciidae, information that is crucial to the design of effective conservation programmes.