Vertical variation in flight activity of the lesser short-tailed bat in podocarp and beech forests, Central North Island, New Zealand

Designing robust monitoring programmes for cryptic species is particularly difficult. Not detecting a species does not necessarily mean that it is absent from the sampling area. A conclusion of absence made in error can lead to misguided inferences about distribution, colonisation and local extinction estimates, which in turn affects where and how conservation actions are undertaken. It is therefore important to investigate monitoring techniques that reduce the non-detection rate of cryptic species. As habitat complexity plays an important role in the activity of bats within a forest, it was hypothesised that the amount of vegetative ‘clutter’ present at different heights within two different forest types affected the flight activity of lesser short-tailed bats (Mystacina tuberculata). This could affect detection of the species within different forest structures. To compare bat activity at three heights – top (22.0–25.0 m), middle (10.0–12.0 m) and bottom (1.5–2.0 m) – within a podocarp and a beech forest we used automatic bat monitors during January to March 2005. The number of bat passes was recorded at each height at two study areas within each forest and compared between forest types. The forest structure was described using the Recce method and vegetative cover estimated within the three height tiers sampled for bat activity. Within both forest types, the middle-level bat detectors logged the greatest amount of activity. However, differences between the forest types were most pronounced closer to the ground, where a high amount of activity was detected within the beech forest, and very little within the podocarp forest. This suggests that flight activity of lesser short-tailed bats may be affected by the level of vegetative clutter found at different heights within a forest. When designing monitoring programmes for lesser short-tailed bats, it is recommended that consideration be given to the forest structure and how this may affect detection of bat activity

Post-translocation assortative pairing and social implications for the conservation of an endangered songbird

Animals translocated for conservation purposes may be sourced from multiple locations which may exhibit inter-site variability in reproductive behaviours. The influence that these differences may have on the propensity of pair formation, and the ultimate impact this may have on the success of the translocation, is unknown due to the low sample sizes of many translocations. We address this knowledge gap by collating an existing 18-year data set documenting multisource translocations of the endangered North Island Kōkako, Callaeas wilsoni, a duetting New Zealand species with known population-specific vocalizations. We found a strong, statistically significant tendency for Kōkako to pair assortatively with respect to source population (like with like) following release. Population-specific differences in sexually selected behaviours that are important in mate choice decisions, such as bird song, are likely the proximate explanation for such reproductive decisions. Accounting for the tendency to pair assortatively following translocation may be particularly important when managing highly vocal animals like Kōkako that produce vocal duets and cooperatively defend territories as mated pairs. Consequently, careful consideration of behavioural variation between translocated individuals should be made, which will appropriately inform decisions relating to release-cohort composition. Failure to consider such variation may negatively impact the success of a translocation as the effective population size of the founder group may be lower than intended. Our findings make an important contribution towards understanding the impact that behavioural variation can have on the conservation of endangered species, and highlight the value of combining long-term data from multiple sources

Conservation implications of song divergence between source and translocated populations of the North Island Kōkako

1. Translocation of individuals from healthy source populations to newly colonize or recolonize suitable habitat is a vital tool for the conservation of a species. Demographic, genetic and landscape factors, but also acoustic signals and cultural factors, will all affect translocation success. 2. We investigated variation in song, and response to song, of the endangered North Island kōkako Callaeas wilsoni (Bonaparte 1850) in New Zealand in two translocated populations and their source population. 3. We found significant vocal variation between the source population and both translocated populations, the latter of which had reduced repertoire sizes and increased repertoire sharing, as well as structurally different song elements of higher frequency and shorter duration. 4. Despite the song divergence and clear variability in the nature and level of response among populations, we did not find any evidence for discrimination against nonlocal song in our reciprocal playback experiments. 5. Synthesis and applications. Vocal divergence and reduced variability in translocated populations suggest founder effects or reduced social interaction rates. The variation could be viewed as cultural erosion and may undermine translocation success. Persistence of response to playback, despite vocal divergence, suggested that social restrictions on gene flow require at least a few decades of separation after translocation. The decision to translocate individuals of threatened species is becoming a more common tool for species conservation world-wide. We argue that it is important to take vocal variation into account during such management decisions as it may affect success of establishment and persistence of translocated populations

Factors affecting post-release dispersal, mortality, and territory settlement of endangered kokako translocated from two distinct song neighborhoods

Animal translocation success rate is generally low, with the causes of failure poorly understood without comprehensive and protracted monitoring. Here we examine the outcome of a translocation of endangered North Island kokako (Callaeas wilsoni) from two adjacent song neighborhoods in New Zealand, each with individual vocal traditions (c. 75% of phrases unshared) to a single release site. We conducted detailed radio-telemetry to monitor post-release dispersal over 50 days during four serial releases of 20 birds while we broadcast neighborhood-specific song around the release site. The birds moved substantial distances after release, however overall short-term release site dispersal was not as great as predicted by a random walk model, suggesting an attraction to playback and/or a reluctance to explore areas away from the release site. This apparent attraction was not specific to a given song neighborhood, however. Although the post-release mortality rate (22% over 31 days) was relatively high in this translocation, we did not detect an effect of sex, age, source origin, or duration of captivity on mortality. We show that habitat use during this acclimation period was disproportionate to availability – the birds’ preferred habitat was similar to that at the capture site. At least four pairs formed, with two and three confirmed breeding in the first and second seasons post-release respectively. Mate choice was non-assortative with respect to song neighborhood, revealing that reduced phrase sharing rates found in adjoining neighborhoods are not a barrier to pair formation. We compare this example with other kokako translocations and make recommendations for future translocations

Triumph displays inform eavesdropping little blue penguins of new dominance asymmetries

Agonistic signals used during contests over important resources have been extensively studied; postconflict signals have received comparatively little attention. While ‘triumph displays’, performed by winners following fights, have been described for many species, no experiment has yet assessed one of the main hypotheses explaining their existence: advertising victory to social eavesdroppers. Our experiments evaluated the impact of triumph calls on the behaviour and stress responses of surrounding penguins. We found that territorial male little blue penguins, Eudyptula minor, having previously been exposed to playback of a vocal exchange between conspecifics followed by the sounds of a fight, had higher heart rates in response to the winner’s call than that of the loser; females had high rates in response to both winners and losers. Males were also less likely to threaten winners than losers vocally during a simulated approach of their burrow, while females remained silent in both contexts. Our findings support the hypothesis that triumph calls facilitate an association of winners’ distinctive vocalizations with stress generated by nearby overt aggression. By advertising their victories, males may establish a ‘reputation’ for winning fights within the social group, potentially reducing the likelihood of being challenged by eavesdroppers in future contests

Songbird cheaters pay a retaliation cost: evidence for auditory conventional signals.

Conventional signals impose costs on senders through receiver retaliation rather than through investment in signal production. While several visual conventional signals have been described (mainly 'badges of status'), acoustic examples are rare; however, several aspects of repertoire use in songbirds are potential candidates. We performed interactive playback experiments to determine whether song-type matches (responding to a song with the same song type), repertoire matches (responding to a song with a different song type, but one in the repertoires of both singers) and unshared song types serve as conventional signals during male-male territorial interactions in banded wrens, Thryothorus pleurostictus. Our results demonstrate that these three signals incite varying levels of receiver aggression: song-type matches induce faster approach than do repertoire matches, and repertoire matches induce faster approach than do unshared song types. Production costs do not differ, while the receiver response does. Because territorial banded wrens approach opponents who signal aggressively, such opponents risk attack. This system will punish and prevent cheaters, as weak males signalling aggression will be subject to escalation by stronger or more-motivated opponents