RESUMO
To reduce the vulnerability of their small body size, common marmosets live in large and cohesive social groups. Thus, we hypothesized that in order to compensate for small body size and predation risk, individuals of common marmosets will stay gathered rather than scattered when foraging for eggs and/or nestling birds. Furthermore, in order to avoid costly injuries and eventual predation risks, for both sides, the majority of interactions among common marmosets and small birds will not involve direct physical contact. The study was developed in a small fragment of Atlantic Forest in the northeast of Brazil. We recorded a total of 115 interactions between common marmosets (Callithrix jacchus) with 7 different bird species. As expected, agonistic interactions were significantly more frequent when the marmosets were gathered. Also, most agonistic interactions by the birds toward common marmosets involved overflights without physical contact. Apparently, the set of avoidance behavior leads to a reduced predation risk for both sides. It appears that dispersed marmosets do not represent an imminent threat that justifies an agonistic reaction by the birds as the latter appear to avoid exposing themselves to unnecessary danger during agonistic interactions, especially when the marmosets are gathered.
Assuntos
Comportamento Agonístico , Aves , Callithrix/psicologia , Cadeia Alimentar , Comportamento Predatório , Animais , Brasil , Feminino , Masculino , Floresta ÚmidaRESUMO
Arboreal primates use loud vocalisations to transmit information in densely vegetated habitats. These vocalisations are likely to show adaptations to increase their propagation and to transmit information. Golden-backed uakaris, Cacajao melanocephalus, emit a loud vocalization termed the "tchó" call, which seems to function as a contact call and encodes information on the individual signaler and behavioural context. Because the call is often used for communication over relatively large distances, we were interested in its propagation in the wild. The aim of the present study was to investigate the degradation patterns of the tchó call in the flooded igapó forest. We examined via playback experiments how the acoustic parameters of this call changed with increasing distance from the playback speaker. We broadcast 12 tchó calls and rerecorded them along a transect at distances of 10, 20, 40, 80 and 160 m from the speaker in two igapó forest patches in Jaú National Park, Amazonas, Brazil. At 160 m from the speaker, the tchó call degraded in both patches and was barely recordable. Up to a distance of 80 m, the bandwidth and number of harmonics in the call decreased with increasing distance, while the lowest frequency increased. The highest frequency (HF) did not gradually decrease with increasing distance. However, when we compared the HF at distances of 10 and 80 m, we could see a clear decrease in this parameter. Call duration increased compared with the broadcast signal up to 40 m because of reverberation, but decreased at 80 m as the weaker echoes of the call attenuated. These changes may reveal information about the signaler's distance during signal transmission. The frequency of maximum energy (FME) of the tchó call decreased significantly when comparing recordings made at 10 and 80 m. Nevertheless, it did not show a consistent and gradual decrease with increasing rerecording distance (at least up to 80 m). FME remained relatively stable (±50 Hz on average, at least up to 80 m) when compared to the other call parameters, suggesting that the tchó call may be adapted to transmit information with some efficiency throughout the igapó forest.