Papers by Torben Dabelsteen
Animal Behaviour, Oct 1, 2000
Communication between territorial songbirds usually involves a transfer of encoded information ov... more Communication between territorial songbirds usually involves a transfer of encoded information over long distances. We would expect coding and decoding strategies to be adaptive given the constraints imposed by the habitat. We used playback to examine some song parameters important for information transfer in the wren, Troglodytes troglodytes. Six stimuli were tested with various modifications to song rhythmicity, song composition, element structure, syntax and overall song spectra. Song features encoding information essential for eliciting a territorial response seemed to be embedded in the fine structure of song elements, that is, their variations in frequency and amplitude over time. To function, this strategy must be flexible enough to accommodate the deleterious effects of habitat-induced degradation. All stimuli composed of original song elements elicited responses regardless of their other alterations. Rhythmicity seemed not to be essential for eliciting territorial behaviour. However, alterations in song rhythmicity, syntax and spectra affected territorial responses, suggesting that these nonessential song parameters do contribute to the options for discrimination.
Marine Ecology Progress Series, Mar 25, 2013
Nielsen et al. (2012; Mar Ecol Prog Ser 453:241−248) analyzed surface observations of harbour por... more Nielsen et al. (2012; Mar Ecol Prog Ser 453:241−248) analyzed surface observations of harbour porpoises in a small coastal area where a modified gillnet was introduced at randomized time intervals. The study concluded that porpoises reacted to the gillnet at surprisingly large distances (in some cases > 80 m). Dawson & Lusseau (2013; Mar Ecol Prog Ser 478:301−302) argue that the conclusions of Nielsen et al. (2012) are undermined by pseudo-replication (a matter of concern in many field studies of marine mammals). We acknowledge these concerns, but we think that the conclusions of Nielsen et al. (2012) remain valid, as the data are best explained by harbour porpoises being able to detect and avoid gillnets at very long ranges.
Behaviour, 2006
Many songbird species use a repertoire of different song types in close-range interactions. In ma... more Many songbird species use a repertoire of different song types in close-range interactions. In male blue tits, Cyanistes caeruleus, this includes songs with and without trill as well as scolding-like vocalizations. We here investigate using playback experiments whether these vocalization types are used at different stages during aggressive interactions, which may be reflected in differential responses of receivers. We predict that territory owning receivers will vary their strength of response with the vocalization type of a simulated intruder and that an aggressive territorial response may include song type matching, i.e. the use of the same vocalization type as the intruder. Supporting the different-signal value hypothesis, scoldinglike playback elicited a stronger approach response of focal males than playback of songs with or without trill. There was no difference in song rate nor do songs without trill elicit a different strength of response than songs with trill. Males did not differ significantly in the amount of song type matching between the treatments but males that landed on the loudspeaker with playback of either songs without trill or scolding-like vocalizations did not match playback songs at all. This suggests a trade-off between approach and song type matching where song type matching is superfluous during very close approaches. Our results may suggest that in the blue tit threat display may be graded from songs with or without trill to scolding-like vocalizations and eventual attack of an intruder.
Behaviour, 2010
Bird songs may vary in amplitude for several reasons. Variations due to differences in environmen... more Bird songs may vary in amplitude for several reasons. Variations due to differences in environmental conditions are well known but whether signal information varies with song amplitude is less well known. In some species quiet songs are heard as a soft twitter. These twitter songs are common in Turdus species and may be used during escalated close range encounters when a quiet song will attract less attention from others. Male redwings (T. iliacus) sing a terminating twitter part that is quieter and highly variable both between and within males compared with the introductory motif part. The twitter song of redwings, however, is often louder than the twitter in other Turdus species, especially during escalated song encounters. The seasonal variation in twitter duration also suggests that the twitter may signal increased aggression. We tested how male redwings responded to an assumed escalation in signalling. In an interactive playback experiment we increased the amplitude of the twitter songs we played back in response to an increase in twitter duration by the subject. Males gave stronger responses to louder twitter. This suggests that twitter amplitude may signal arousal in male redwings.
Journal of Avian Biology, Mar 1, 2000
Populations of Reed Buntings Emberiza schoeniclus in the western Palearctic are classified in two... more Populations of Reed Buntings Emberiza schoeniclus in the western Palearctic are classified in two major subspecies groups according to morphology: northern migratory schoeniclus and Mediterranean resident intermedia. Songs of the two groups differ mainly in complexity and syllable structure, with intermedia songs being more complex. We explored the possibilities of song as a subspecies isolating mechanism by testing if male schoeniclus Reed Buntings reacted differently to field playbacks of songs from their own subspecies group, from the foreign subspecies group and from a control species, the Yellowhammer Emberiza citrinella. We tested 30 different males, each with a different song belonging to one of the three categories: own, foreign and Yellowhammer. Unlike songs of the two subspecies groups, Yellowhammer song elicited no response. Differences between reactions to own and foreign subspecies group songs were not significant, even though differences in response type (singing vs approaching) suggested some degree of uncertainty in classification of foreign song. We conclude from these results that the subspecies may be only in the first stages of the isolation process.
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, Nov 12, 2010
The cetacean brain is well studied. However, few comparisons have been done with other marine mam... more The cetacean brain is well studied. However, few comparisons have been done with other marine mammals. In this study, we compared the harp seal (Pagophilus groenlandicus) and the harbor porpoise brain (Phocoena phocoena). Stereological methods were applied to compare three areas of interest: the entire neocortex and two subdivisions of the neocortex, the auditory and visual cortices. The total number of neurons and glial cells in the three regions was estimated. The main results showed that the harbor porpoise have an estimated 14.9 Â 10 9 neocortical neurons and 34.8 Â 10 9 neocortical glial cells, whereas the harp seal have 6.1 Â 10 9 neocortical neurons and 17.5 Â 10 9 neocortical glial cells. The harbor porpoise have significantly more neurons and glial cells in the auditory cortex than in the visual cortex, whereas the pattern was opposite for the harp seal. These results are the first to provide estimates of the number of neurons and glial cells in the neocortex of the harp seal and harbor porpoise brain and offer new data to the comparative field of mammalian brain evolution.
BMC Biology, Nov 5, 2008
Background: Given the costs of signalling, why do males often advertise their fighting ability to... more Background: Given the costs of signalling, why do males often advertise their fighting ability to rivals using several signals rather than just one? Multiple signalling theories have developed largely in studies of sexual signals, and less is known about their applicability to intra-sexual communication. We here investigate the evolutionary basis for the intricate agonistic signalling system in eland antelopes, paying particular attention to the evolutionary phenomenon of loud knee-clicking. Results: A principal components analysis separated seven male traits into three groups. The dominant frequency of the knee-clicking sound honestly indicated body size, a main determinant of fighting ability. In contrast, the dewlap size increased with estimated age rather than body size, suggesting that, by magnifying the silhouette of older bulls disproportionately, the dewlap acts as an indicator of age-related traits such as fighting experience. Facemask darkness, frontal hairbrush size and body greyness aligned with a third underlying variable, presumed to be androgen-related aggression. A longitudinal study provided independent support of these findings. Conclusion: The results show that the multiple agonistic signals in eland reflect three separate components of fighting ability: (1) body size, (2) age and (3) presumably androgen-related aggression, which is reflected in three backup signals. The study highlights how complex agonistic signalling systems can evolve through the simultaneous action of several selective forces, each of which favours multiple signals. Specifically, loud knee-clicking is discovered to be an honest signal of body size, providing an exceptional example of the potential for non-vocal acoustic communication in mammals.
Habitat selection of the European bison has until now mainly been studied in the Carpathian Mount... more Habitat selection of the European bison has until now mainly been studied in the Carpathian Mountains and in the Polish and Belarusian Bialowieska Forest, where the bison selected deciduous forest-dominated habitats with a preference for complex mosaics of forest and patches of grass in the vegetative season. In May 2012, the Danish Nature Agency Bornholm introduced seven European bison to an enclosure in Almindingen Forest with the aim of creating a more open and natural forest. We examined habitat selection of two of the bison, a male and a female, which were both radio-collared, and used population extrapolation to investigate the potential of the herd as ecosystem engineers. We found that the two bison in the vegetative season spent most of their time in coniferous (45%), uncultured cut coniferous (25%) and deciduous habitat (24%). Compared with the habitat availability in the enclosure, the two bison preferred uncultured cut coniferous forest habitat. This preference may gradually lead to a more open and natural Almindingen Forest, as requested by the Danish Nature Agency Bornholm.
Journal of Mammalogy, Nov 1, 2003
Vocal individuality has been found in a number canid species. This natural variation can have app... more Vocal individuality has been found in a number canid species. This natural variation can have applications in several aspects of species conservation, from behavioral studies to estimating population density or abundance. The swift fox (Vulpes velox) is a North American canid listed as endangered in Canada and extirpated, endangered, or threatened in parts of the United States. The barking sequence is a long-range vocalization in the species' vocal repertoire. It consists of a series of barks and is most common during the mating season. We analyzed barking sequences recorded in a standardized context from 20 captive individuals (3 females and 17 males) housed in large, single-pair enclosures at a swift fox breeding facility. Using a discriminant function analysis with 7 temporal and spectral variables measured on barking sequences, we were able to correctly classify 99% of sequences to the correct individual. The most important discriminating variable was the mean spacing of barks in a barking sequence. Potential applications of such vocal individuality are discussed.
Biological Cybernetics, Oct 1, 1985
A new method for computerized modification of sound signals is presented. With digital signal pro... more A new method for computerized modification of sound signals is presented. With digital signal processing in the time domain it is possible to alter the amplitude, the frequency and the time scale of natural sounds independently. The method can be applied to natural sounds with reasonably pure tonal quality.
Bioacoustics-the International Journal of Animal Sound and Its Recording, 2003
Animal Behaviour, Feb 1, 2008
In species where individuals are widely spaced instantaneous signals cannot readily form the basi... more In species where individuals are widely spaced instantaneous signals cannot readily form the basis of communication networks, that is several individuals within signalling range of each other. However, markings, signals that remain in the environment after the signaller has left, may fulfil this role. In this study, we have investigated the possible function of swift fox, Vulpes velox, latrines, collections of scat, urine and possibly other secretions, in a communication network context. We found that latrines had higher frequencies of occurrence inside the core (defined as the 50% kernel contour) of a pair's home-range when compared with outside the core and in areas of a pair's home-range that overlapped with neighbouring individuals when compared with those areas that did not overlap with neighbours. These were also the two areas where latrines were most likely to reoccur in the next consecutive breeding season. Furthermore, latrines in the exclusive part of a pair's home-range core and latrines in edge area overlap zones had the highest frequency of visits as determined by the rate of faecal depositions. Our interpretation of these results is that latrines possibly have a dual function. That is, they function in territory defence in the exclusive areas of a pair's core and as centres for information exchange in the outer areas of a pair's home-range that overlap with neighbouring foxes. We discuss the possible information content of latrines and the possibility of latrines forming the basis of communication networks in the swift fox.
Proceedings of The Royal Society B: Biological Sciences, Dec 7, 2011
Male sexual harassment of females is common across sexually reproducing species and can result in... more Male sexual harassment of females is common across sexually reproducing species and can result in fitness costs to females. We hypothesized that females can reduce unwanted male attention by constructing a social niche where their female associates are more sexually attractive than themselves, thus influencing the decision-making of males to their advantage. We tested this hypothesis in the Trinidadian guppy (Poecilia reticulata), a species with high levels of male sexual harassment. First, we confirmed that nonreceptive females were harassed less when they were paired with a more sexually attractive (receptive) female than with another non-receptive female. We then found that, indeed, females exploit this as a strategy to reduce sexual harassment; non-receptive females actively preferred to associate with receptive over non-receptive females. Importantly, when given access only to chemosensory cues, non-receptive females still showed this preference, suggesting that they use information from chemical cues to assess the sexual attractiveness of potential female partners. Receptive females in contrast showed no such preferences. Our results demonstrate that females can decrease male harassment by associating with females that are more sexually attractive than themselves and that they perform active partner choices based on this relative attractiveness. We propose that this strategy is likely to represent an important pathway by which females can construct social niches that influence the decision-making of others to their advantage; in this case, to reduce the sexual harassment they experience.
Animal Behaviour, May 1, 2007
Discrimination between conspecifics is important in mediating social interactions between several... more Discrimination between conspecifics is important in mediating social interactions between several individuals in a network environment. In great tits, Parus major, females readily distinguish between the songs of their mate and those of a stranger. The high degree of song sharing among neighbouring males, however, raises the question of whether females are also able to perceive differences between songs shared by their mate and a neighbour. The great tit is a socially monogamous, hole-nesting species with biparental care. Pair bond maintenance and coordination of the pair's reproductive efforts are important, and the female's ability to recognize her mate's song should therefore be adaptive. In a neighbouremate discrimination playback experiment, we presented 13 incubating great tit females situated inside nestboxes with a song of their mate and the same song type from a neighbour. Each female was tested in two trials with the opposite order of stimulus presentation. Eleven females responded to the song of their mate in both trials, while two females responded to those of their mate in one trial and a neighbour in the other. Thus, great tit females are able to perceive subtle individual differences between their mate's song and a neighbour's rendition of the same song type despite being inside nestboxes, which are known to alter the received song structure and intensity. We suggest that this female discrimination ability inside nest holes is mediated by a high perceptual sensitivity towards small variations in song structure that should be adaptive to this hole-nesting bird species.
Animal Behaviour, Feb 1, 2002
Unmated male whitethroats court females with a special display in which the male dives towards th... more Unmated male whitethroats court females with a special display in which the male dives towards the female while singing a quiet and complex song, the diving song. Observations of natural interactions suggest that females can affect males' courtship behaviour by making dscharp-calls or ze-calls and by making short jumps towards the diving males. We tested this in an interactive experiment where jumps and calls were presented in different combinations to unmated territorial males. Jumps were presented by means of a stuffed female mounted on a remotely controlled device, and calls were played back from a speaker placed beneath the stuffed female. Female calls and jumps had a strong but differential effect on male courtship. Playback of dscharp-calls attracted the attention of males and hence caused them to perform courtship sooner and jumps increased the number of diving songs, whereas ze-calls resulted in more males attempting copulation with the stuffed female.
The Condor, Feb 1, 2004
Female Magnificent Frigatebirds (Fregata magnificens) search for mates while flying and by visiti... more Female Magnificent Frigatebirds (Fregata magnificens) search for mates while flying and by visiting males at their display sites. Males respond with an intense courtship display that includes making a characteristic drumming sound and presenting the inflated gular pouch, a likely sexually selected trait. Viewing angle, male posturing, and proximity might, however, limit females' ability to appraise pouch size exactly. We investigated whether drumming provides the same information about pouch size and indeed found fundamental frequencies to be negatively correlated with estimated pouch sizes. Probably, the gular pouch functions as a resonance chamber. Females' assessment of gular pouch size could therefore be enhanced by the combination of visual and auditory signals.
Applied Animal Behaviour Science, Aug 1, 2016
Abstract Individuals of the same species vary consistently in their behaviour across time and con... more Abstract Individuals of the same species vary consistently in their behaviour across time and context, and this is often referred to as animal personality. In this study, we investigate animal personality based on the definition of personality traits as underlying dispositional factors, which are linked to biological internal factors that are stable and perhaps heritable. Although not directly measurable, these underlying dispositional factors predispose individuals to react through different behavioural patterns. We investigated the shyness-boldness continuum reflected in the consistency across time of the inter-individual variation in behavioural responses towards two different novelty tests: a novel object test representing non-social contexts and a mirror test representing social contexts. Our study animals were 60 farmed American mink (Neovison vison), which were raised in identical housing conditions. We recorded the approach behaviour of the mink towards novelty at two different times: the first time during non-breeding season in December 2013 and the second time during pre-breeding season in February 2014. Behavioural variables were analysed using principal component analyses and our results show consistency in inter-individual variation in shyness measures across seasons. This consistency differed across non-social and social contexts forming two different shyness-boldness dimensions as were also found across context in a previous study. To our knowledge this is the first study to reveal aspects of the shyness-boldness continuum across time and season in the American mink from non-breeding season in December to pre-breeding season in February. Our study confirms the existence of personality in farmed American mink, but interestingly, we saw a shift in the positioning of most individuals from shy to more bold on the shyness continuum when comparing the December measures to the February measures. This shift was further supported by the results of a simple stick test, which indicated a change towards a higher responsiveness towards humans in the pre-breeding season.
Behavioural Processes, Nov 1, 2001
The importance of intrasexual differences in repertoire size was investigated in a playback exper... more The importance of intrasexual differences in repertoire size was investigated in a playback experiment with whitethroats, Syl6ia communis. Fourteen unmated territorial males received three treatments: a small repertoire, a large repertoire, and a small-elongated repertoire where the last couple of elements had been repeated to give songs of about the length of large repertoire playback. Besides responding to the intruder's absolute repertoire size or song length, males might also take their own singing ability into consideration. Therefore, the playback was considered relative to the repertoire size and song length of the territory defending males. However, this seems not to have had an important effect on the response. There was a stronger response to large than to small repertoire playback and a stronger response to small-elongated than to small repertoire playback, whereas there was no difference between large and small-elongated repertoire playback. In general, the strongest response was given to playback of long song (large and small-elongated song repertoire), suggesting that males responded to song length rather than repertoire size in short-term interactions with an intruder. This agrees with the idea that song length indicates the degree of arousal of the singer. The lack of response to repertoire size suggests that the evolution of the complex song repertoire in whitethroats' motif song is not a result of intrasexual selection.
PLOS ONE, Nov 21, 2012
Parrots in captivity are known for their ability to vocally imitate humans and recently it has be... more Parrots in captivity are known for their ability to vocally imitate humans and recently it has been shown that wild-living orange-fronted conures are able to immediately imitate other individuals' contact calls. The function of this exceptional ability to imitate remains unclear. However, orange-fronted conures live in fission-fusion flocks where they encounter many different individuals every day, and it is possible that their vocal imitation ability is a flexible means to address a specific individual within a flock. We tested this via playback to short-term captive wild conures. Test birds were placed together in pairs in outdoor aviaries to form simple flocks. To simulate imitation of a specific individual these pairs received playback of contact calls that primarily imitate one of the two birds. Overall, individuals that received simulated vocal imitations of its calls responded more frequently and faster than the other individual. This suggests that orange-fronted conures can use imitations of contact calls to address specific individuals of a flock. In the discussion we argue that the fission-fusion flock dynamics of many parrot species has been an important factor in evolving conures' and other parrots' exceptional ability to imitate.
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Papers by Torben Dabelsteen