Playback Experiments Research Articles

The Inquiline Ant Myrmica karavajevi Uses Both Chemical and Vibroacoustic Deception Mechanisms to Integrate into Its Host Colonies.

Simple SummaryAlthough fiercely defended by workers, ant societies can be infiltrated by social parasites that exploit the whole colony and its resources, instead of taking advantage of a single organism. Among them, we studied Myrmica karavajevi, a rare ant species in which the worker caste does not exist, and queens live as “inquilines” within colonies of another ant species, commonly Myrmica scabrinodis. Parasite queens entirely depend on host worker labour. They have evolved many adaptations to be admitted and integrate as members of the host ant society. Indeed, we found that, even at the pupal stage, the parasite is treated as a valuable item in the colony hierarchy, as it is rescued ahead of the colony’s own brood. Moreover, we discovered that M. karavajevi adult queens use two strategies to live undisturbed in the host nest. The parasite smells like the host queens by possessing specific odours and produces sounds similar to those emitted by M. scabrinodis ants, particularly by queens. Through these kinds of mimicking, M. karavajevi advances its rank towards the highest attainable position in the colony’s hierarchy. M. karavajevi is an outstanding example of multimodal deception, which needs a combined behavioural and molecular approach to be fully unravelled.Social parasitism represents a particular type of agonistic interaction in which a parasite exploits an entire society instead of a single organism. One fascinating form of social parasitism in ants is the “inquilinism”, in which a typically worker-less parasitic queen coexists with the resident queen in the host colony and produces sexual offspring. To bypass the recognition system of host colonies, inquilines have evolved a repertoire of deceiving strategies. We tested the level of integration of the inquiline Myrmica karavajevi within the host colonies of M. scabrinodis and we investigated the mechanisms of chemical and vibroacoustic deception used by the parasite. M. karavajevi is integrated into the ant colony to such an extent that, in rescue experiments, the parasite pupae were saved prior to the host’s brood. M. karavajevi gynes perfectly imitated the cuticular hydrocarbon profiles of M. scabrinodis queens and the parasite vibroacoustic signals resembled those emitted by the host queens eliciting the same levels of attention in the host workers during playback experiments. Our results suggest that M. karavajevi has evolved ultimate deception strategies to reach the highest social status in the colony hierarchy, encouraging the use of a combined molecular and behavioural approach when studying host–parasite interactions.

Interspecific aggression in sympatry between congeneric tropical birds

AbstractInterspecific aggression may shape species distributions through competitive exclusion, resulting in spatial segregation, or facilitate sympatry as an adaptive mechanism for resource partitioning. Competitive exclusion results from asymmetric aggression of one species towards another, but if the aggressive relationship between species is symmetric, they may persist in sympatry. Interspecific aggression is widely cited as a mechanism for maintaining the distributional limits of tropical birds, but how it shapes the spatial dynamics of competing species that are sympatric over larger geographic areas is less clear. To address this issue, we conducted reciprocal playback experiments on two congeneric Antbirds — Thamnophilus atrinucha and T. doliatus — that occur in sympatry across a habitat matrix in Colombia to characterize their relationship as symmetrically or asymmetrically aggressive and analyzed point count data to assess the degree to which they occur sympatrically. We found weak evidence for competitive exclusion, with the larger T. doliatus responding asymmetrically to T. atrinucha, and the two species having a low co-detection rate during point counts. However, despite their 22% difference in body size, T. atrinucha still responded to T. doliatus playback in over half of our trials, and the two species co-occurred on nearly 25% of point counts, indicating that interspecific aggression does not drive complete spatial segregation. Our findings highlight how the degree to which one species can competitively exclude another may vary, especially across a dynamic landscape.

Short-term predation risk and habitat complexity influence cheetah antipredator behaviours

Animals can reduce predation risk by increasing antipredator behaviours in areas of high long-term risk (risky places hypothesis), escalating antipredator behaviours when exposed to immediate risks (risky times hypothesis), varying responses to short-term risk based on long-term risk (risky times and risky places hypothesis, or predation risk allocation hypothesis) or altering antipredator behaviours based on habitat characteristics (habitat complexity risk mediation hypothesis). Most research on responses to predation risk has come from studies on herbivore prey, whereas little research has focused on mesopredator behavioural responses to risk. We studied antipredator behaviours of mesopredator cheetahs, Acinonyx jubatus , exposed to top predator risk from lions, Panthera leo , and leopards, Panthera pardus , by using a playback experiment to manipulate short-term predation risk in areas of differing long-term risk. We did not find support for the risky places hypothesis; cheetah vigilance was not influenced by long-term risk. On the contrary, we found support for the risky times hypothesis; cheetahs were more vigilant and more likely to flee following lion and leopard playbacks. Additionally, we did not find support for the risky times and risky places hypothesis or the predation risk allocation hypothesis; cheetah antipredator behaviours following a predator playback were not associated with long-term predation risk. Finally, cheetahs had higher baseline vigilance in areas of open vegetation but were more likely to flee from lion sounds in areas of dense vegetation and from leopards in areas of open vegetation. We highlight the importance of understanding spatial and temporal factors that influence mesopredator risk perception and show that antipredator behaviours can differ among trophic levels. • Cheetahs vary antipredator behaviours based on short-term risk and habitat features. • Cheetahs increased vigilance and were likely to flee following predator playbacks. • Long-term risk of encountering top predators did not influence cheetah vigilance. • Cheetahs were more likely to flee from leopard playbacks in open habitats. • Cheetahs were more likely to flee from lion playbacks in dense vegetation.

Response to heterospecific calls in non‐passerine species: can two Rallidae species recognise each other based on their vocalisations?

AbstractCommunication is generally assumed to be the domain of conspecific signallers and receivers that produce reliable signals and respond adaptively. However, interactions between coexisting species can be surprisingly complex, suggesting that animals not only perceive but also selectively respond to signals produced by other species. Many species respond to the vocalisations of heterospecifics, but it is usually difficult to separate actual vocal recognition from the response resulting from misidentification. We controlled this bias in a playback experiment with two sympatric Rallidae species, the water rail (Rallus aquaticus) and little crake (Zapornia parva). Both focal species produced more calls and little crake additionally approached the speaker more often in response to calls of each other than to calls of closely related but non‐sympatric spotted crakes (Porzana porzana) or the sympatric but non‐competing little grebes (Tachybaptus ruficollis). By contrast, when responding to each other's calls water rails produced fewer loud calls than during the conspecific treatment suggesting that focal birds were merely announcing their presence, whereas little crakes produced mainly alarms suggesting that they communicated with the mated partner to warn it rather than with the heterospecific intruder. We conclude that focal Rallidae species could distinguish not only their calls from those of conspecifics, but also each other's calls from those of other sympatric and phylogenetically related species.

The role of introductory alarm calls for song discrimination in Ficedula flycatchers

Assortative mating depends on species distinctiveness in mating traits and preferences, which can be challenging to maintain when traits and/or preferences are learned. This is because learning may cause individuals to copy heterospecific signals. Juvenile songbirds possess innate sensory biases favouring them to learn and to prefer conspecific songs, but the effectiveness of these biases relies on consistent and sufficient differences between the songs produced by different species. However, mating signals, including learned songs, sometimes converge in sympatry, and the species-specific cues that individuals use to shape their preferences are often unknown. In Ficedula flycatchers, a stereotyped and highly species-specific alarm call is often incorporated as the first syllable of their songs. However, where the two species co-occur, pied flycatchers, Ficedula hypoleuca , learn to incorporate the introductory calls of the closely related collared flycatcher, Ficedula albicollis , into their songs. In this study, we investigated the role of introductory alarm calls for song discrimination in collared flycatchers, using playback experiments of both manipulated and unmanipulated songs on adults and nestlings within the hybrid zone of Öland, Sweden. We predicted that the introductory alarm call would be sufficient to trigger song responses, such that adults and nestlings would respond similarly to song phrases including the call, whether it is followed by conspecific or heterospecific notes. Our results provide evidence that the introductory alarm call is sufficient to trigger song discrimination in nestlings, but not in adult males, potentially due to their greater experience with songs and, therefore, subtler discrimination. Altogether, this study highlights the often-overlooked importance of calls within or associated with songs. • Collared flycatchers often start their songs with an alarm call. • The alarm call seems sufficient to drive song responses in nestlings. • We argue that the call could guide learning onto appropriate songs. • However, the call alone is unlikely to be sufficient for discrimination in adults. • We discuss the broader implication of incorporation of calls into songs.

Follow the leader? Orange-fronted conures eavesdrop on conspecific vocal performance and utilise it in social decisions

Animals regularly use social information to make fitness-relevant decisions. Particularly in social interactions, social information can reduce uncertainty about the relative quality of conspecifics, thus optimising decisions on with whom and how to interact. One important resource for individuals living in social environments is the production of information by signalling conspecifics. Recent research has suggested that some species of parrots engage in affiliative contact call matching and that these interactions may be available to conspecific unintended receivers. However, it remains unclear what information third parties may gain from contact call matching and how it can be utilised during flock decisions. Here, using a combined choice and playback experiment, we investigated the flock fusion choices and vocal behaviour of a social parrot species, the orange-fronted conure (Eupsittula canicularis), to a contact call matching interaction between two individuals of different sexes and with different vocal roles. Our results revealed that orange-fronted conures chose to follow vocal leaders more often than vocal followers during fusions. Furthermore, flocks responded with higher call rates and matched the stimulus calls closer when subsequently choosing a vocal leader. Interestingly, orange-fronted conures also showed higher contact call rates and closer matches when choosing males over females. These results suggest that paying attention to conspecific contact call interactions can provide individuals with social information that can be utilised during fission and fusion events, significantly influencing the social dynamics of orange-fronted conures.

Females and males respond differently to calls impaired by noise in a tree frog.

Both human and nonhuman animals communicating acoustically face the problem of noise interference, especially anurans during mating activities. Previous studies concentrated on the effect of continuous noise on signal recognition, but it is still unknown whether different notes in advertisement calls impaired by noise affect female choice and male–male competition or not. In this study, we tested female preferences and male‐evoked vocal responses in serrate‐legged small tree frog (Kurixalus odontotarsus), by broadcasting the five‐note advertisement call and the advertisement call with the second, third, or fourth note replaced by noise, respectively. In phonotaxis experiments, females significantly discriminated against the advertisement call with the fourth note impaired by noise, although they did not discriminate against other two calls impaired by noise, which indicates that the negative effect of noise on female preference is related to the order of impaired notes in the advertisement call. In playback experiments, males increased the total number of notes in response to noise‐impaired calls compared with spontaneous calls. More interestingly, the vocal responses evoked by noise‐impaired calls were generally similar to those evoked by complete advertisement calls, suggesting that males may recognize the noise‐impaired calls as complete advertisement calls. Taken together, our study shows that different notes in advertisement calls replaced by noise have distinct effects on female choice and male–male competition.

Learning in advance? Interspecific recognition ability in male Eurasian blackcaps

Interspecific aggression is common in bird communities. It is thought to be a consequence of learned behavior or misdirected intraspecific aggression. In the former case birds acquire the ability to identify individuals of other species by social learning of species-specific traits during interactions with heterospecifics in a shared habitat. I conducted a two-choice song playback experiment to investigate the role of associating signals from two sensory modalities, auditory and visual, in shaping the agonistic response of male Eurasian Blackcaps (Sylvia atricapilla) to simulated male Garden Warbler (S. borin) intruders. I measured focal males’ response to playbacks to the song of a Blackcap or a Garden Warbler while giving them a choice between stuffed male models of both species presented in their territories. The experiments were carried out in early spring, before the arrival of Garden Warblers from Africa. I found that male Blackcaps were able to associate species-specific songs with species-specific plumage types. The ability to associate signals characterized not only experienced after-second-year old males, but also second-year old males that had not had the opportunity to defend breeding territories against heterospecifics. This suggests that second-year old male Blackcaps acquire the ability to associate Garden Warbler song with plumage before they use this skill when defending territory during their first breeding episode. Male Blackcaps do not mistake male Garden Warblers for males of their species, but rather learn these associations during the first months of life. However, the possibility that these associations are innate cannot be excluded.

Contextual variations in calls of two nonoscine birds: the blue petrel Halobaena caerulea and the Antarctic prion Pachyptila desolata

Abstract Bird vocalizations are critical cues in social interactions as they convey temporary information varying with the social context, for example, the signaler motivation when facing a rival or a potential mate. To date, literature mainly focused on learning birds. Burrowing petrels (Procellariidae) are nonlearning birds with a limited vocal repertoire. Bachelor males communicate with conspecifics with a single call emitted in three situations: in the absence of a certain auditory (spontaneous calls), toward females (female-directed calls), and toward males (male-directed calls). We first hypothesized that, although the call structure is preserved, temporal and spectral parameters vary between the three call types of bachelor males, translating different motivations (Motivation Hypothesis). To go further, we hypothesized that acoustic variations in male-directed calls indicate the signaler’s aggressive motivation and, therefore, the variations are similar whether calls are produced by breeder or bachelor males (Breeding Status Hypothesis). We tested the two hypotheses performing field playback experiments on two petrel species: the blue petrel (Halobaena caerulea) and the Antarctic prion (Pachyptila desolata). Despite the obvious call stereotypy, we observed temporal variations and frequency shifts when males react to a female or a male, which may translate the sexual or aggressive motivation of the signaler. Furthermore, the similarity of variations in male-directed calls of both breeder and bachelor males suggests the aggressive motivation. So far, vocal plasticity in nonlearning birds has been greatly underestimated. Here, we highlighted the expression of different motivations through vocal variations and the ability to produce frequency variations in species with genetically coded vocalizations.

An independent experiment does not support stress-mediated kin discrimination through red squirrel vocalizations

A wide range of species have been found to differentiate kin from nonkin. However, the ability to recognize kin, or the costs and benefits of discriminating kin from nonkin may depend on particular extrinsic environmental or intrinsic physiological conditions, resulting in context-dependent kin discrimination. North American red squirrels, Tamiasciurus hudsonicus, have previously been shown to be capable of discriminating the territorial calls of kin and nonkin. More recently, post hoc analysis of existing data suggested that kin discrimination might depend on the state of the caller (i.e. acute stress). Here we tested this hypothesis with independently collected data from a repeated-measures playback experiment and found no evidence in support of acute stress mediating kin discrimination. While squirrels were shown to register and respond to playbacks, exposure to a trapping/handling stressor in the caller had no effect on the receiver's response to the calls of kin and nonkin. Furthermore, we found no overall discrimination between the calls of kin and nonkin. These independently collected data instead suggest that the previous post hoc finding consistent with context-dependent kin discrimination was likely a spurious relationship associated with the data from which the post hoc hypothesis was generated rather than representing a real biological relationship. Our findings from this study emphasize the importance of testing post hoc hypotheses with independent experiments.

A desert songbird with no confamilials in the Western Hemisphere (Verdin,Auriparus flaviceps) investigates divergent conspecific songs

AbstractMost birds that show geographic variation in their songs discriminate between local and foreign songs, which may help them avoid unnecessary conflicts with vagrant individuals or similar-sounding congeners. However, some species respond equally to foreign and local songs, which may be useful if foreign individuals present territorial threats or if there are no sympatric congeners to avoid. Species without sympatric congeners are not commonly tested in playback studies, but they offer an opportunity to see how song variation and recognition unfolds when the pressure to avoid similar congeners is absent. Here, we use Verdins (Auriparus flaviceps), a monotypic genus of songbird with no confamilials in North America, to explore song variation and recognition in a species living without close relatives. We assessed geographic variation in song across the Verdin range and conducted a playback experiment using exemplars from 2 acoustically divergent and geographically distant regions as treatments. We found significant geographic variation in song that mapped well onto ecologically distinct desert regions. We found that Verdins had stronger vocal responses to local-sounding songs, but had equal movement responses to local-sounding and foreign songs. These results are similar to results found in other species without sympatric congeners and provide an example of a species that investigates acoustically divergent conspecific songs, despite recognizing salient differences in those songs.

Glucocorticoid-Mediated Changes in Male Green Treefrog Vocalizations Alter Attractiveness to Females.

Adrenal glucocorticoids (GCs) are increasingly recognized as important modulators of male courtship signals, suggesting that circulating levels of these steroids can play a central role in sexual selection. However, few studies have examined whether GC-mediated effects on male sexual signals actually impact mate choice by females. Here, we examine how corticosterone (CORT)-mediated changes in the vocalizations of male green treefrogs, Dryophytes cinereus, influence attractiveness to females. In this species, agonistic acoustic signaling between rival males competing for mates increases circulating CORT levels in contest losers. Acute elevations in CORT, in turn, decrease the duration of male advertisement calls and increase the latency between successive calls, resulting in a net reduction in vocal effort (the amount of signaling per unit time) that occurs independently of changes in circulating androgens. Based on known preferences for acoustic features in D. cinereus, and other anuran species, the direction of CORT-mediated effects on temporal call characteristics is expected to compromise attractiveness to females, but whether they are of sufficient magnitude to impact female mate choice decisions is unclear. To examine whether CORT-mediated effects on male advertisement calls reduce attractiveness to females, we broadcast vocalizations in dual speaker playback experiments approximating the mean and 1 SD above and below the mean call duration and vocal effort values (the two primary vocal features impacted by elevated CORT) of males with low and high CORT levels. Results revealed strong preferences by females for the calls characteristic of males with low CORT in tests using the approximate mean and 1 SD above the mean call duration and vocal effort values, but females did not show a preference for calls of males with low CORT in trials using call values approximating 1 SD below the mean. Overall, females preferred males with signal traits predictive of low CORT, however this effect was nonlinear with attenuated preferences when signal alternatives differed only marginally indicating a possible thresholding effect. Specifically, females appeared to discriminate between males with low versus high CORT based primarily on differences in call rates associated with CORT-mediated changes in call duration and vocal effort. Our results highlight that changes in circulating CORT during male-male vocal interactions can decrease attractiveness to females, suggesting that circulating levels of CORT can play a critical role in both intra- and intersexual selection.

Synchrony of complex signals in an acoustically communicating katydid.

The ability to entrain to auditory stimuli has been a powerful method to investigate the comparative rhythm abilities of different animals. While synchrony to regular simple rhythms is well documented, synchrony to complex stimuli, with multiple components at unequal time intervals, is rarer. Several katydid species with simple calls have been shown to achieve synchrony as part of their natural calling interactions in multi-individual choruses. Yet no study so far has demonstrated synchrony in any insect with a complex call. Using natural calling behaviour and playback experiments, we investigated acoustic synchrony and the mechanisms underlying it in the katydid species Mecopoda 'Two Part Caller'. This species has a complex call consisting of a long trill followed by two or more chirps. We found that individual males synchronized trills and, to a lesser extent, chirps. Further investigation of trill synchrony showed that the timing of trills is modified by external trills but not chirps. Chirp synchrony is modified by external chirps, but also by trills. We suggest a qualitative two-oscillator model underlying synchrony in this species and discuss the implications for the evolution of acoustic synchrony.

Processes underlying complex patterns of song trait evolution in a Setophaga hybrid zone.

During secondary contact between two species when hybrids are less fit than parents, mating signals are expected to diverge, while aggressive signals are expected to converge. If a single signal trait is used in both mating and aggression, then the dynamics between these two forces could influence the evolutionary trajectory of that trait. We studied such a situation in an avian hybrid zone between two Setophaga species, where birdsong is used in both mate attraction and territory defense. We hypothesized that song modules of the two species will show separate and distinct geographic patterns due to the influence of selective pressures for effective territorial aggression and for effective mate attraction. We conducted geographic cline analyses and playback experiments across this hybrid zone. We found an unexpected geographic pattern of asymmetric introgression of song rhythm, which may be explained by results of the playback experiments that suggest that differences in song rhythm serve a greater role in mate attraction than in territory defense. In contrast, differences in syllable morphology show little evidence of importance in mate attraction or territorial defense. Song features converge in the hybrid zone, yet patterns of trait change suggest that the song production modules may vary in their modes of development and inheritance. Syringeal motor gesturing, which gives rise to syllable morphology, shows a nonclinal mosaic pattern, suggesting that this trait may be predominantly learned. In contrast, respiratory patterning, which forms song rhythm, shows a clinal geographic transition, suggesting that this trait could be more innate. The results indicate that opposing forces act independently on song via distinct modules of the song production mechanism, driving complex patterns of song trait evolution.

Not only a listener: female frog-biting midges (Corethrellidae) also distinguish the shape of frogs

AbstractIt is well known that female adults of frog-biting midges (Corethrellidae) are attracted by anuran mating calls. However, the role of host-emitted cues other than mating calls in determining the level of attraction remains poorly understood. Here, we performed field playback experiments to test how the host-seeking behaviour of Corethrella Coquillett is influenced by different sound stimuli: mating call of a tree frog, cricket call, and no sound. Then, after long-distance host detection, we evaluated if Corethrella can distinguish landing sites by using at short distance the colour and/or shape of anurans. For that, we placed artificial models of frogs with different colours (light green and dark brown) and an artificial caterpillar model (light green colour) on the top of speakers. We found that only frog mating calls presented with the visual cue of an artificial frog were attacked by Corethrella, suggesting that frog shape, regardless of colour, is an important cue for the identification of its hosts. This is the first study providing evidence that after flying long distances guided by frog calls, Corethrella can identify their hosts using visual cues at short distances.

Noise-Related Song Variation Affects Communication: Bananaquits Adjust Vocally to Playback of Elaborate or Simple Songs

Birds communicate through acoustic variation in their songs for territorial defense and mate attraction. Noisy urban conditions often induce vocal changes that can alleviate masking problems, but that may also affect signal value. We investigated this potential for a functional compromise in a neotropical songbird: the bananaquit (Coereba flaveola). This species occurs in urban environments with variable traffic noise levels and was previously found to reduce song elaboration in concert with a noise-dependent reduction in song frequency bandwidth. Singing higher and in a narrower bandwidth may make their songs more audible in noisy conditions of low-frequency traffic. However, it was unknown whether the associated decrease in syllable diversity affected their communication. Here we show that bananaquits responded differently to experimental playback of elaborate vs. simple songs. The variation in syllable diversity did not affect general response strength, but the tested birds gave acoustically distinct song replies. Songs had fewer syllables and were lower in frequency and of wider bandwidth when individuals responded to elaborate songs compared to simple songs. This result suggests that noise-dependent vocal restrictions may change the signal value of songs and compromise their communicative function. It remains to be investigated whether there are consequences for individual fitness and how such effects may alter the diversity and density of the avian community in noisy cities.

Anyone listening? No evidence for eavesdropping on male singing interactions in the great tit, Parus major

Observing interactions between others can provide important information to individuals. Male songbirds often engage in singing contests where they vary the type and timing of signals and provide eavesdropping individuals with information about their competitiveness. How this information is used and its effect on subsequent spatial behaviour and reproductive decisions of eavesdroppers is not well understood. Here we tested whether great tits use information gathered by eavesdropping on male singing interactions to assess rivals and (potential) mates. We used interactive playback experiments to engage territorial males in song contests with either a more (song overlapping and more persistent singing) or less challenging (song alternating and less persistent singing) intruder. We followed male and female movements by automated radiotracking, determined paternity using microsatellite analysis and maternal investment by quantifying egg weights and provisioning behaviour. We expected that mates of males exposed to the challenging treatment would subsequently foray more often off territory to assess other males and potential extrapair mates and invest less in their broods. Moreover, we expected that neighbours would adjust their foraying behaviour according to information gained by eavesdropping. Females, however, did not alter their foraying behaviour or brood investment and neither female nor male neighbours changed their visiting behaviour to playback territories. Our results provide no evidence that females used information gathered by eavesdropping on asymmetric song interactions in reproductive decisions or that song interactions affected movements across territories in the neighbourhood. Overlapping or singing for a longer time on an intruded upon territory may not always be perceived as a higher level of threat, and reproductive decisions and assessment of familiar individuals are likely to be based on multiple sources of information rather than on a single interaction.

Cooperation-based concept formation in male bottlenose dolphins

In Shark Bay, Western Australia, male bottlenose dolphins form a complex nested alliance hierarchy. At the first level, pairs or trios of unrelated males cooperate to herd individual females. Multiple first-order alliances cooperate in teams (second-order alliances) in the pursuit and defence of females, and multiple teams also work together (third-order alliances). Yet it remains unknown how dolphins classify these nested alliance relationships. We use 30 years of behavioural data combined with 40 contemporary sound playback experiments to 14 allied males, recording responses with drone-mounted video and a hydrophone array. We show that males form a first-person social concept of cooperative team membership at the second-order alliance level, independently of first-order alliance history and current relationship strength across all three alliance levels. Such associative concepts develop through experience and likely played an important role in the cooperative behaviour of early humans. These results provide evidence that cooperation-based concepts are not unique to humans, occurring in other animal societies with extensive cooperation between non-kin.

Song divergence indicates an unclear relationship between the Neotropical and Nearctic Horned Larks

BackgroundSome studies have indicated that the Horned Larks (Eremophila alpestris) should be considered as a species complex. Recently it split into four species or clades and seven subclades based on genetic, morphological, and biogeographic data. However, other aspects like song divergence have not been studied and several subspecies have not been evaluated, leading to important information gaps in this group of birds. In this work, we aimed to assess the differences in song traits and playback response between the Nearctic subclade and the Neotropical or Colombian subspecies E. a. peregrina.MethodsWe compared six song traits between these groups and performed field playback experiments, to test the response of the Neotropical larks to both songs. We tested the difference in the variables for separate as well as by principal component analysis (PCA).ResultsWe found significant differences (p < 0.05) in the individual song traits and the PCA analysis between the two groups. Further, the PCA analysis showed a clearer divergence of the Neotropical songs in comparison to the Nearctic songs of different locations within North America. Similarly, the playback analysis showed a significantly lower response of E. a. peregrina to the songs of the Nearctic larks.ConclusionsBesides this song divergence, there are important ecological and biogeographic differences between the Neotropical and Nearctic Horned Larks, that indicate an unclear relationship between these two groups. Thus, further morphological and genetic studies are required to clarify the taxonomy of the Neotropical Horned Lark and define if they share the same evolutionary history as the other subspecies of the Nearctic subclade.

Contrasting use of space by two migratory Afro-Palearctic warblers on their African non-breeding grounds

In migratory birds, constraints due to breeding are relaxed during the non-breeding season and thus, social behaviours and spatial associations are potentially more directly coupled to food resources and habitats. Use of space and territorial behaviour has rarely been studied in Afro-Palearctic migrants. Variation in strategies could exist among species within the same habitat because of differences in foraging, diet and microhabitat. We compare use of space and association with conspecifics in Common Chiffchaffs Phylloscopus collybita and Subalpine Warblers Sylvia cantillans at a non-breeding site in northern Senegal using radio telemetry and playback experiments. Home ranges of Chiffchaffs were larger and overlapped more than those of Subalpine Warblers. Though Chiffchaffs were often close together, we found no signs of spatial association among individuals in either species. Chiffchaffs showed no clear pattern of territorial response to conspecific song; whereas, playback elicited a territorial response in most Subalpine Warblers. Our results suggest species-specific differences in use of space that might reflect differences in foraging ecology and microhabitat.