In conditions of poor visibility, animals can determine their location using sounds. If there are sound sources with a relatively fixed location in their environment, these might be used as landmarks ...with respect to which the individual could locate new sound sources. However, unlike visual orientation, surprisingly little is known about the use of acoustic landmarks. We studied the use of calling neighbours for orientation in the corncrake, Crex crex, a highly territorial species that calls in long sequences in loose and stable groups at night and in tall grass. In two experiments with remote multichannel playback, we mimicked artificial interactive networks. In the first experiment, we tested whether the number of neighbours affects the accuracy of locating an intruder and we showed that males are more efficient at locating new intruders when there are more vocally active neighbours in their vicinity. In the second experiment, we tested the influence of the amplitude of neighbours' calls on the assessment of the distance to the intruder. We showed that the response to an intruder depends on the ratio of the amplitude of the intruder's calls to the amplitude of the neighbours' calls. Our results therefore indicate that corncrakes orient themselves in the environment using calling neighbours as landmarks and we suggest that the use of the communication network as a network of acoustic landmarks can be an alternative mechanism of orienting using sounds in conditions of limited visibility.
•We studied the use of calling neighbours for orientation in the corncrake.•We used multichannel playback and we mimicked artificial interactive networks.•Males were more efficient at locating intruders when there were more neighbours.•Males used the amplitude of neighbours when assessing the distance to an intruder.
Agricultural intensification is threatening ecosystems and causing the collapse of farmland birds. Biodiversity-rich, semi-natural grasslands dramatically decreased in recent decades and were either ...intensified, replaced by more remunerative crops or abandoned. We investigated the factors driving habitat selection by corncrake Crex crex, a flagship species for grassland conservation, in Trentino (Italy, European Alps), considering topography, public payments through Rural Development Programme (RDP), agro-botanic grassland types and farming intensification, during 2010–2018. Topographical variables were the most important predictors, but a synthetic model combining different predictors was even more supported. Elevation (negatively) and solar radiation (positively) affected occurrence; untargeted subsidies for grassland mowing had a negative effect, whereas specific subsidies for the management of Natura 2000 grasslands had a positive effect. Stocking density (livestock units/ha), taken as a direct measure of intensification, had a negative impact on occurrence. Corncrakes preferred unfertilized grasslands, then species-rich grasslands with little fertilization; mountainside and, especially, valley-floor grasslands were under-selected. Corncrake has progressively disappeared from Trentino’s valley-floors, ‘shifting’ to mountain areas, but the effects of topography remind it is a lowland species pushed towards uplands by farming intensification, which is now affecting also the ‘mountain refugia’. Grassland types are selected by the species according to a gradient from unmanaged to heavily managed; subsidized mowing and livestock units/ha, a proxy for the amount of fertilizers and timing/frequency of mowing, had negative impacts. The conservation of the Alpine corncrake population and associated biodiversity critically depends on the maintenance of low-intensity farming on a relevant portion of cultivated grasslands. The reduction of fertilization, the adaptation of mowing regimes (to avoid early mowing, close subsequent cuts and homogeneous cutting over large areas), and the broader adoption of biodiversity-targeted payment schemes are urgently required. Grasslands at relatively moderate elevation and sun-exposed are particularly important: lowering management intensity there is crucial for conservation.
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•We investigated habitat selection by corncrake Crex crex in Italian Alps.•RDP subsidies for mowing: untargeted, negative impact; for Natura 2000, positive.•Stocking density (representing intensification) had a negative impact.•Unfertilized/species-rich grassland, low elevation and high solar radiation preferred.•Corncrakes and associated biodiversity depend on low-intensity farming grassland.
Source–filter theory assumes that calls are generated by a vocal source and are subsequently filtered by the vocal tract. The air in the vocal tract vibrates preferentially at certain resonant ...frequencies, called formants. Formant frequencies can be a good indicator of the caller's characteristics, such as sex, age, body size or individual identity. Although source–filter theory was originally proposed for mammals, formants are also observed in birds, and some bird species have been shown to perceive formants. In this study, we evaluated the hypotheses that formant frequencies (1) are an indicator of body size and (2) can be used for individual discrimination by a nocturnal bird species, the corncrake (Crex crex). We analysed calls of 104 males from Poland and the Czech Republic. Linear regression models showed that the males with a longer head (including the bill length) had a significantly lower formant dispersion and lower fourth and fifth formant frequencies. However, we found no significant relationships between body weight and any filter‐related acoustic measurement. The formant frequencies had smaller within‐ than between‐individual coefficients of variation. This characteristic of the formant frequencies implies a high potential for individual coding. A discriminant function analysis correctly assigned 94.8% of the calls to the caller based on formants from second to fifth. Our results indicated that the formant frequencies are a weak indicator of the body size of the sender in the corncrake. However, even weak dependence between body size and acoustic properties of signal may be important in natural selection process. Alternatively, such a weak dependence may be observed, because receivers ignore the acoustical, formant‐based cues of body size. Simultaneously, the formants might potentially provide acoustic cues to individual discrimination and could be used to census and monitoring tasks.
•Agri-environment measures suitable for Corncrakes are available in the majority of European regions.•Agri-environment measures cover less than 10% of the European Corncrake population.•Coverage had ...no visible effect on regional population trends.•Conservation should recognise large-scale processes and populations outside EU.
The Corncrake Crex crex breeds mainly in managed grasslands in Europe. Agri-environment schemes (AES) were introduced in many European countries to protect broods from earlier and more frequent mowing. In order to assess the efficacy of these AES on the scale of regional populations, we obtained information on current AES options for Corncrakes in 33 countries and administrative regions within the European Union (EU) and European free Trade Association (EFTA) using a questionnaire. Options suitable for Corncrake conservation were available in 18 regions, but coverage of the regional Corncrake populations was highly variable. Coverage with AES was high in selected western regions, but low throughout eastern Europe where most Corncrakes breed. The various suitable options together covered only 6.2% of the total Corncrake population inside the EU and EFTA. While AES were effective at restoring Corncrake populations in Scotland, no evidence was found for effects on populations in other EU regions.Limited coverage of Corncrake populations in countries holding the largest populations, as well as its low breeding-site fidelity suggest that the Corncrake’s future is not secured by the current extent of AES. If current farming practices in eastern European countries become more intensive as expected, the species’ future may be at risk. Besides developing AES which are more attractive to farmers and better targeting the requirement of Corncrakes, conservation of farmland birds in Europe should pay more attention to continent-wide changes of breeding conditions in order to be successful.
The acoustic adaptation hypothesis is based on the assumption that senders are directionally selected to maximize transmission and minimize degradation; however, the two aims are not necessarily ...convergent. In complex habitats, where more effects that might potentially cause attenuation and degradation co‐occur and longer transmission must incur a higher cost, signals should attenuate faster and have shorter transmission ranges. At the same time, such signals should be more resistant to degradation in order to preserve their communicatory function. Based on a sound transmission experiment, we tested the evidence for these predictions using territorial calls of three sympatric species of rails, inhabiting habitats with increasing complexity: Corncrake Crex crex, Spotted Crake Porzana porzana and Water Rail Rallus aquaticus. In the experiment, the calls were broadcasted with similar amplitudes through a heterogeneous habitat inhabited by all three species and rerecorded at different distances up to 320 m. Despite standardized amplitudes and habitats, calls of the species living in simpler habitats had longer transmission ranges but were more susceptible to degradation than calls of the species living in more complex habitats. Our results suggest that narrow frequency bandwidth is an adaptation of species inhabiting complex habitats that helps their calls to degrade less at the cost of stronger attenuation and shorter transmission range. By contrast, wide frequency bandwidth extends the range but increases degradation and thus it is used only by species inhabiting structurally simpler habitats. This study shows that, in more complex habitats, the clarity of the message is preserved at the cost of range.
•Postponing first mowing dates reduced departure probability of male Corncrakes.•Late mowing implies economical losses for farmers and land use cessation expanded.•On unused meadows preferred habitat ...conditions deteriorated.•Calling sites were abandoned by male Corncrakes after few years without land use.•Habitat conservation should promote late mowing, e.g. by combustion of biomass.
Land use intensification caused severe population declines in many grassland bird species. For the Corncrake, a multi-brooded, ground-breeding rail that inhabits mostly agricultural grassland, more frequent mowing at earlier dates is a threat to nests and broods and induces dispersal of adults. We used an occupancy model that allows for staggered arrival and departure times to estimate within-season movements of male Corncrakes and analysed how departure probabilities, calling site occupancy and habitat suitability were affected by land use. This study covered two study periods before (1998–2000) and after (2012–2015) a change in the local management regime. Male Corncrakes showed continuous arrival and departure during the breeding season, but delayed mowing dates reduced departure probability in the second study period, which should enhance the probability for second broods because less calling sites were affected by mowing especially during early July. Late mowing, however, implies economical losses for farmers and cessation of land use expanded. On unused meadows litter heights increased and plant species richness and forb cover declined, thus preferred habitat conditions deteriorated. Calling sites in unmanaged meadows were abandoned by male Corncrakes after few years without land use. Postponing first mowing dates until broods fledge is effective in protecting Corncrake broods, because more chicks should have survived until fledging but habitat quality depends on annual management. Because currently mowing late in the season is unattractive to farmers, we suggest that future Corncrake habitat conservation should along with financial compensations promote and evaluate the utilization of late-cut biomass for energy production.
The behaviour of most animals has evolved in a communication network environment, in which signals produced by senders are perceived by many intended and unintended receivers. In this study, we ...tested whether the corncrake (Crex crex), a nocturnal rail species with innate (non-learned) calls, is able to eavesdrop on the interactions of conspecific males and how this eavesdropping affects subsequent responses by the eavesdropper to territorial intrusion. In the first step, simulated aggressive or neutral interactions between male dyads were presented to a focal male. In the second step, the calls of winning, losing or neutral males from the first step were played within the territory of the focal male. We measured behavioural and vocal responses of focal males. We found that corncrakes eavesdropped on signal exchange between rivals. Males often began responding to distant aggressive interactions during the eavesdropping phase, and they responded strongly during the intrusion phase of the experiments. The response was significantly weaker to playback of males from neutral interactions than to those involved in aggressive interactions, and we found no differences between the responses to Winners and Losers entering a focal male territory.
Understanding patterns of genetic structure, gene flow and diversity across a species range is required to determine the genetic status and viability of small peripheral populations. This is ...especially crucial in species distributed across a large range where spatial heterogeneity makes it difficult to predict the distribution of genetic diversity. Although biogeographical models provide expectations of how spatially structured genetic variation may be at the range scale, human disturbance may cause strong deviations from these theoretical predictions. In this study, we investigated genetic structure and demography at a pan-European scale in the corncrake Crex crex, a grassland bird species strongly affected by agricultural changes. We assessed population structure and genetic diversity, as well as demographic trends and direction of gene flow, in and among 15 contemporary populations of this species. Analyses revealed low genetic structure across the entire range with high levels of genetic diversity in all sites. However, we found some evidence that the westernmost populations were, to a very limited extent, differentiated from the rest of the European population. Demographic trends showed that population numbers have decreased in western Europe and remained constant across eastern Europe. Results may also indicate asymmetric gene flow from eastern to western populations. In conclusion, we suggest that the most likely scenario is that contrasting demographic regimes between eastern and western populations, driven by heterogeneous human activity, has caused not only asymmetric gene flow that has buffered small peripheral populations against genetic diversity loss, but also erased any genetic structure that may have existed. Our study not only highlights the need for coordinated action at the European scale to preserve source populations of the corncrake, but also to ensure persistence of the most threatened sites. Only by doing so will we avoid losing adaptive potential and prevent over-reliance on eastern source populations whose future may be uncertain.
•Understanding range-scale genetic patterns is essential in conservation biology.•Predictions of biogeographical models can be disturbed by human activity.•In the corncrake Crex crex, we observed a low genetic structure at the European scale.•Approximate Bayesian computation informed about gene flow and demographic trends.•European-scale coordination is needed for efficient conservation of the corncrake.
The first national Corncrake Crex crex survey in Slovenia was performed in 1992/93, followed by further five in 1999, 2004, 2010, 2015 and 2020. In 2004, annual monitoring of eight most important ...Corncrake Natura 2000 sites (SPAs) began. Both datasets showed a moderate population decline since 1992. After Slovenia’s accession to the EU in 2004, Corncrake population steeply declined at SPA Breginjski Stol and moderately declined at SPA Dobrava - Jovsi due to scrub encroachment, whereas moderate decline at SPA Ljubljansko barje can be attributed mostly to intensive grassland management and the conversion of grasslands to arable land, resulting in nest and habitat destruction. In 2020, the number of calling males in Slovenia was smaller by 55 % compared to 1999, when the highest number ever was recorded (683). The highest average number of Corncrakes in the 1992–2021 period was counted at SPA Ljubljansko barje (139 calling males/year), whereas the smallest number was recorded at SPA Snežnik - Pivka (8 calling males/year). A comparison of target values for Corncrake population size on individual SPAs from the national Natura 2000 management programme for the 2015–2020 period with counted population sizes showed that, with the exception of SPA Lake Cerknica, all SPAs are falling behind the target values by 32–90%, depending on the site. Likewise, the majority of sites are far from reaching target values for the enrolment of agri-environmental measure VTR (first cut after 1 Aug). The article also discusses the weaknesses of current VTR, its reform in 2021, as well as other potential measures and financial sources for Corncrake conservation.
Low-amplitude vocalizations produced during aggressive encounters, courtship, or both (quiet/soft songs) have been described for many species of song-learning passerines; however, such signals have ...not been studied among nonlearning birds. During aggressive interactions, apart from using the broadcast call, male corncrakes (Crex crex) produce a low-amplitude, gurgling-mewing call, which appears to be equivalent to soft songs of songbirds. Previous studies have shown that low-amplitude vocalizations are reliable signals of aggressive motivation. It is unclear, however, how the reliability of such signals is maintained. We experimentally tested whether males that use soft calls are more likely to attack later on and whether males respond differently to natural calls consisting of both broadcast and soft elements and to their modified versions where the soft elements were removed. Senders were more likely to attack the speaker if they earlier produced soft calls. Receivers were more likely to attack the speaker or retreat the speaker if the playback included soft calls. These results show that soft call is a signal of aggressive motivation in the corncrake, and we argue that the reliability of this signal is maintained by a receiver-retaliation rule.
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