Michał Budka

Functionally similar acoustic signals in the corncrake (Crex crex) transmit information about different states of the sender during aggressive interactions.

We combined playback experiments with hormonal manipulations to study the information content of acoustic signals during aggressive interactions between male corncrakes. During territorial conflicts, fights are uncommon, but the intensity of signaling usually increases. Such signals can be temporally and contextually associated with many aggressive behaviors and most likely function as threats or as indicators of the senders quality or motivation. However, such correlational data are unsatisfactory for the proper interpretation of the function and information content of signals. Experimental tests are required to determine whether signals and aggressive behaviors are controlled by common or independent mechanisms. In our experiment, we assigned subjects to four groups: testosterone-implanted birds, flutamide-implanted birds, birds with empty implants, and non-captured control birds. Males produced two types of calls (quiet soft calls and loud broadcast calls), both of which are known to be reliable predictors of aggressive escalation. When testosterone action was blocked with flutamide, males significantly limited the amount of time spent close to the playback speaker and stopped responding to playback with soft calls. Broadcast calling was unaffected by the blockage of testosterone. Conversely, increased levels of testosterone neither affected calling nor the time spent near the speaker, indicating a permissive, rather than a graded effect of androgens. We concluded that, despite the seemingly similar function, both signals may transmit information about different states of the sender; soft calls seem to imply a threat of force, while broadcast calls appear to be more similar to an announcement, which is only indirectly associated with a males aggressive behavior.

Microgeographic call variation in a non-learning species, the Corncrake (Crex crex)

AbstractMicrogeographic variation in bird song has been studied in many species. However, it remains to be more fully described in birds that do not learn song and that thus have largely innate vocalisations. In this study, we focused on microgeographic variation in the territorial calls of one such non-learning species, the Corncrake (Crex crex). We examined the temporal and spectral characteristics of male Corncrake calls recorded in five separate populations in Poland. We found significant but weak relationships between some of the call characteristics and between-caller distances in four populations. The patterns observed were inconsistent. For some call characteristics, similarity decreased as distance between callers increased, while the opposite was true for other characteristics. Moreover, the same call characteristics showed opposite patterns in different populations or even within the same population but in different years. These findings suggest that the specific spatial distribution of the different quality habitats in which populations are located may have a crucial influence on microgeographic variation in calls. Alternatively, in non-learning species, various levels of microgeographic variation in calls might arise independently as a consequence of (1) social interactions among males, during which birds modify some parameters of their inherited call; or (2) territory occupancy patterns that minimize or maximize call similarity among neighbours.ZusammenfassungMikrogeographische Unterschiede in den Rufen einer nicht-lernenden Art, dem Wachtelkönig Mikrogeographische Unterschiede im Gesang von Vögeln wurden in vielen Arten untersucht. Sie müssen jedoch eingehender beschrieben werden für Arten, die ihren Gesang nicht lernen und daher größtenteils angeborene Lautäußerungen haben. In dieser Untersuchung konzentrierten wir uns auf mikrogeographische Unterschiede in den Territorialrufen einer solchen Art, dem Wachtelkönig (Crex crex). Wir untersuchten die zeitlichen und spektralen Eigenschaften von Rufen männlicher Wachtelkönige, aufgenommen in fünf verschiedenen Populationen in Polen. Wir fanden signifikante aber schwache Beziehungen zwischen einigen der Eigenschaften der Rufe und dem Abstand zwischen den Rufern in vier Populationen. Die beobachteten Muster waren inkonsistent. Für einige der Rufeigenschaften nahm die Ähnlichkeit mit steigendem Abstand zwischen den Rufern ab, während für andere das Gegenteil der Fall war. Darüber hinaus zeigten dieselben Rufeigenschaften gegensätzliche Muster in unterschiedlichen Populationen oder sogar innerhalb derselben Population in unterschiedlichen Jahren. Diese Ergebnisse legen nahe, dass die spezifische räumliche Verteilung der Habitate von unterschiedlicher Qualität, in der sich die verschiedenen Populationen befinden, einen entscheidenden Einfluss haben könnte auf mikrogeographische Unterschiede in den Rufen. Alternativ könnten verschiedene Ausprägungen von mikrogeographischen Unterschieden zwischen den Rufen nicht-lernender Arten unabhängig zutage treten als Folge von (1) sozialen Interaktionen zwischen Männchen, in denen die Vögel einige Parameter ihrer angeborenen Rufe anpassen, oder (2) von Mustern der Besetzung von Territorien, welche die Ähnlichkeit von Rufen zwischen Nachbarn minimieren oder maximieren.

Should I stay or should I go? Territory settlement decisions in male Corncrakes Crex crex

ABSTRACT Capsule: Corncrake Crex crex males shift their territories and change habitat preferences across the breeding season as a consequence of anthropogenic pressure and/or to enhance the chances of reproduction through sequential polygamy. Aims: To examine how habitat structure changed during the breeding season, whether Corncrake males responded to those changes and which habitat features were crucial when males settled and occupied territories. Methods: Calling male Corncrakes were surveyed six times during the breeding season. In each location where a calling male was recorded, the habitat and vegetation structure was described from one to three times during the season. Results: Corncrake males avoided extremely wet and extremely dry habitats, whereas large sedge and reed communities were much more preferred. There were significant seasonal changes in the density of vegetation and moisture content. Males were more sedentary at the beginning of the breeding season. Males significantly changed habitat preferences in short-periods of time. However, none of the habitat-related features explained whether males stayed or left the territory. Conclusion: Corncrakes shift their territories during the breeding season in response to anthropogenic pressure (agricultural activity) as well as changes in water levels during the year. However, territorial shifts within seasons might also be caused by the appearance of fertile females in different habitats at different stages of the breeding season.

Vocal individuality in drumming in great spotted woodpecker—A biological perspective and implications for conservation

Animals—including conservation biologists—use acoustic signals to recognise and track individuals. The majority of research on this phenomenon has focused on sounds generated by vocal organs (e.g., larynx or syrinx). However, animals also produce sounds using other parts of the body, such as the wings, tail, legs, or bill. In this study we focused on non-syrinx vocalisation of the great spotted woodpecker, called drumming. Drumming consists of strokes of a bill on a tree in short, repeated series, and is performed by both males and females to attract mates and deter rivals. Here, we considered whether the great spotted woodpecker’s drumming patterns are sex-specific and whether they enable individual identification. We recorded drumming of 41 great spotted woodpeckers (26 males, 9 females, 6 unsexed). An automatic method was used to measure the intervals between succeeding strokes and to count strokes within a drumming roll. The temporal parameters of drumming that were analysed here had lower within- than between-individual coefficients of variation. Discriminant function analyses correctly assigned 70–88% of rolls to the originating individual, but this depended on whether all individuals were analysed together or split into males and females. We found slight, but significant, differences between males and females in the length of intervals between strokes—males drummed faster than females—but no difference in the number of strokes within a roll. Our study revealed that temporal patterns of drumming in the great spotted woodpecker cannot be used for unambiguous sex determination. Instead, discrimination among individuals may be possible based on the intervals between strokes and the number of strokes within a roll. Therefore, it is possible that differences in the temporal parameters of drumming may be used by birds to identify each other, as well as by researchers to aid in census and monitoring tasks.