Discrimination and ejection of eggs and nestlings by the fan-tailed gerygone from New Caledonia

Nestling rejection is a rare type of host defense against brood parasitism compared with egg rejection. Theoretically, host defenses at both egg and nestling stages could be based on similar underlying discrimination mechanisms but, due to the rarity of nestling rejector hosts, few studies have actually tested this hypothesis. We investigated egg and nestling discrimination by the fan-tailed gerygone Gerygone flavolateralis, a host that seemingly accepts nonmimetic eggs of its parasite, the shining bronze-cuckoo Chalcites lucidus, but ejects mimetic parasite nestlings. We introduced artificial eggs or nestlings and foreign gerygone nestlings in gerygone nests and compared begging calls of parasite and host nestlings. We found that the gerygone ejected artificial eggs only if their size was smaller than the parasite or host eggs. Ejection of artificial nestlings did not depend on whether their color matched that of the brood. The frequency of ejection increased during the course of the breeding season mirroring the increase in ejection frequency of parasite nestlings by the host. Cross-fostered gerygone nestlings were frequently ejected when lacking natal down and when introduced in the nest before hatching of the foster brood, but only occasionally when they did not match the color of the foster brood. Begging calls differed significantly between parasite and host nestlings throughout the nestling period. Our results suggest that the fan-tailed gerygone accepts eggs within the size range of gerygone and cuckoo eggs and that nestling discrimination is based on auditory and visual cues other than skin color. This highlights the importance of using a combined approach to study discrimination mechanisms of hosts.     

ACOUSTIC COMMUNICATION SIGNALS OF MYSTICETE WHALES

ABSTRACT

Mysticete (baleen) whales produce a variety of vocalizations and sounds, but relatively few of these have been well described with accompanying behavior. This review concentrates on the vocalizations consistently associated with behavioral interactions or acoustic exchanges between or among conspecifics. These communication “signals” have been categorized for this review as contact calls of single animals outside of the breeding season (including cow-calf pairs), vocalizations reported during the breeding season (often designated as “songs”), and calls produced by active groups of whales that may or may not have a reproductive function. While much remains unknown, the data obtained thus far indicate that the social vocalizations of baleen whales have structural/functional similarities with those of other mammals and birds.     

FRIENDS OF WILDLIFE SOUND AT NSA

ABSTRACT

The problem of categorization arises in any classification system because classes should be discrete while the characteristics of most natural objects and aspects of nature are more or less gradual. In systematics, this problem usually is solved by creating several levels of categories, such as class, order, family, genus and species. In the existing killer whale discrete call classification, only two levels occur—call type and call subtype. In this paper we describe structural categories at a broader level than call type in the discrete sounds of killer whales and compare these categories between and within vocal clans in a community of resident killer whales from Southeast Kamchatka, Russian Far East, and also with killer whales outside this community. We found four main classes of discrete calls in the repertoire of resident killer whales from Southeast Kamchatka. The calls of Southeast Kamchatka transient killer whales and Sakhalin killer whales do not fall into these classes. This suggests that the resident killer whale community from Southeast Kamchatka has some rules defining the structure of calls which are typical for this community. Consequently, all resident killer whales from Southeast Kamchatka can be said to share the same vocal tradition.     

Are vocal characteristics related to leadership patterns in mixed‐species bird flocks?

What structures the organization of mixed‐species bird flocks, so that some ‘nuclear’ species lead the flocks, and others follow? Previous research has shown that species actively listen to each other, and that leaders are gregarious; such gregarious species tend to make contact calls and hence may be vocally conspicuous. Here we investigated whether vocal characteristics are associated with leadership, using a global dataset of mixed‐species flock studies and recordings from sound archives. We first asked whether leaders are different from following or occasional species in flocks in the proportion of the recordings that contain calls (n = 58 flock studies, 145 species), and especially alarm calls (n = 111 species). We found that leaders tended to have a higher proportion of their vocalizations that were classified as calls than occasional species, and both leaders and following species had a significantly higher proportion of their calls rated as alarms compared to occasional species. Next, we investigated the acoustic characteristics of flock participants’ calls, hypothesizing that leaders would make more calls, and have less silence on the recordings. We also hypothesized that leaders’ calls would be simple acoustically, as contact calls tend to be, and thus similar to each other, as well as being detectable, in being low frequency and with high frequence bandwidth. The analysis (n = 45 species, 169 recordings) found that only one of these predictions was supported: leading species were less often silent than following or occasional species. Unexpectedly, leaders’ calls were less similar to each other than occasional species. The greater amount of information available and the greater variety of that information support the hypothesis that leadership in flocks is related to vocal communication. We highlight the use of sound archives to ask questions about behavioral and community ecology, while acknowledging some limitations of such studies.     

Hearing in the FM-bat Phyllostomus discolor: a behavioral audiogram

Absolute auditory thresholds of six adult lesser spear-nosed bats Phyllostomus discolor (Chiroptera, Phyllostomidae) were determined in a two-alternative forced-choice procedure. Behavioral responses to pure tone stimuli could be elicited throughout the tested frequency range of 5–142 kHz. The shape of the average audiogram is characterized by two sensitivity peaks and a pronounced increase of thresholds around 55 kHz, and towards the limits of the tested frequency range. The spectral extent of both sensitivity peaks shows a close relation to the bandwidth of two types of species-specific vocalizations. The first low threshold area (> 10 and < 55 kHz) of the audiogram seems perfectly adapted to the directive call used for intraspecific communication, whereas the second sensitivity peak, centered around 85 kHz, covers most of the bandwidth of the species' echolocation calls.Abbreviations CF constant frequency - FM frequency modulation - l left - r right - SPL Sound pressure level     

Intergroup calls of male pig-tailed langurs (Simias concolor)

Pig-tailed langurs (Simias concolor) were observed in the Pagai Islands and in Siberut. They lived in 1-male groups containing from one to five or more females plus their young. Adult males produced loud vocalizations of the sortGautier andGautier (1977) called “type 1 loud calls.” The pig-tailed langur's type 1 loud call (TOLC) was a series of 2 to 25 nasal barks, the loudest of which could be heard for 500 m or more in the rain forest. Exchange of TOLC's between males was the only frequent intergroup interaction. Fifty-one percent of TOLC's were emitted spontaneously, 33% occurred in response to TOLC's of other males, 13% to falling trees, 4% in response to thunder, and 1% during a fight between males of different groups. Although TOLC's occurred throughout the day, they exhibited a bimodal distribution, with a peak of calling early in the morning, and another in late afternoon. Tape-recorded TOLC's played back in the field stimulated males hearing them to emit TOLC's of their own. Barks in experimentally-elicited TOLC's were delivered at a faster rate than barks in other TOLC's were. While TOLC's mediate intergroup communication among males, field playback experiments are needed to truly elucidate their functions.     

Resource partitioning of sonar frequency bands in rhinolophoid bats

Summary In the Constant Frequency portions of the orientation calls of various Rhinolophus and Hipposideros species, the frequency with the strongest amplitude was studied comparatively. (1) In the five European species of the genus Rhinolophus call frequencies are either species-specific (R. ferrumequinum, R. blasii and R. euryale) or they overlap (R. hipposideros and R. mehelyi). The call frequency distributions are approximately 5–9 kHz wide, thus their ranges spead less than ±5% from the mean (Fig. 1). Frequency distributions are considerably narrower within smaller geographic areas. (2) As in other bat groups, call frequencies of the Rhinolophoidea are negatively correlated with body size (Fig. 3). Regression lines for the genera Rhinolophus and Rhinolophus, species from dryer climates have on the average higher call frequencies than species from tropical rain forests. (4) The Krau Game Reserve, a still largely intact rain forest area in Malaysia, harbours at least 12 syntopic Rhinolophus and Hipposiderso species. Their call frequencies lie between 40 and 200 kHz (Fig. 2). Distribution over the available frequency range is significantly more even than could be expected from chance alone. Two different null hypotheses to test for random character distribution were derived from frequency-size-relations and by sampling species assemblages from a species pool (Monte Carlo method); both were rejected. In particular, call frequencies lying close together are avoided (Figs. 4, 5). Conversely, the distribution of size ratios complied with a corresponding null hypothesis. This even distribution may be a consequence of resource partitioning with respect to prey type. Alternatively, the importance of these calls as social signals (e.g. recognition of conspecifics) might have necessitated a communication channel partitioning.     

Loud calls ofGalago crassicaudatus andG. garnettii and their relation to habitat structure

Long distance vocalizations have been shown to be good indicators of genetic species in primates. Here the loud calls of two recently identified greater galago taxa —Galago crassicaudatus andG. garnettii — are compared and analyzed statistically. Observed differences in call structures are investigated further as potential indicators of differences in the structures of habitats frequented by the two species. Although the calls share a repetitive structure, and show similar dominant frequency bands (1,000 – 1,500 Hz), they differ significantly in the number of units per call, unit duration, inter-unit interval, highest frequency, lowest frequency, dominant frequency band, first harmonic, and call duration. The duration of theG. crassicaudatus call is more than twice that ofG. garnettii. Strong intraspecific consistency is seen in the most energetic frequency bands (dominant frequency band and first harmonic), and durations of the individual units and inter-unit intervals. Information important to species recognition is thus most likely to be contained in these features. Individual recognition may be encoded in the relative emphasis of higher level harmonics. The frequency structures of the calls will reflect requirements for acoustical transmission in a forest environment, as well as structural constraints imposed by body size. Higher frequencies detected in theG. garnettii call (up to 8,500 Hz) may have a functional significance related to distance estimation, or may simply be a reflection of smaller body size. The greater modulation of theG. garnettii call suggests that its habitat constitutes a denser or more turbulent medium for sound transmission than does the habitat ofG. crassicaudatus.