Animal movements at large spatial scales are of great importance in population ecology, yet little is known due to practical problems following individuals across landscapes. We studied the whole Norwegian population of a small songbird (ortolan bunting, Emberiza hortulana) occupying habitat patches dispersed over nearly 500 km2. Movements of colour‐ringed males were monitored during ten years, and extensive long‐distance dispersal was recorded. More than half of all cases of breeding dispersal took place within one breeding season, and males moved up to 43 km between singing territories, using 1–22 d. Natal dispersal was usually to a habitat patch close to the natal patch, or within the natal patch if it was large. Breeding dispersal movements were often long‐distance, beyond neighbouring patches, and up to 11–19 patches were overflown. Movements of at least 6–9 km across areas of unsuitable habitat occurred regularly. The number of patches visited was low (1–4) even though search costs in terms of time spent moving from one site to another were relatively low (often only a few days even for distances >10 km). Most males seemed to use a threshold tactic when choosing a patch, but returns to previously visited patches were recorded, including some cases of commuting. In conclusion, male ortolan buntings have a surprising ability to move quickly at the landscape level, and this resulted in a high connectivity of patches. We discuss our results in relation to optimal searching strategies, in particular the use of within‐breeding season versus post‐breeding season search, conspecific attraction and adaptive late arrival of young birds.
Several studies demonstrated that bird song functions as a first line of territorial defence. The efficiency of deterring rivals depends strongly on the strategy of singing used (e.g. alternating/overlapping singing, singing with low/high rate, matching song type of a rival or singing different type). Causes of between males variation during countersinging are still not fully understood, especially when different signals have similar production costs and their meaning is assigned by arbitrary convention (conventional signalling). We tested whether an oscine bird with small repertoire size, the ortolan bunting Emberiza hortulana, differentiate strategy of responding to song of an intruder in relation to its age and threat value of signals. We performed playback experiments to measure response of second year (SY) and after second year (ASY) males to a song of low (eventual variety singing) and high (immediate variety singing) threat value. We found substantial differences in response to playback, which were related both to the type of stimuli used and age of responding males. Both SY and ASY males gave more calls than songs in response to immediate variety playback, which suggest stronger vocal response to the signal of higher threat value. Approaching loudspeaker was similar for both age classes when lower threat value signal was played back, while simultaneously SY males clearly avoided approaching loudspeaker when stronger threat values signal was played back. We conclude that ortolan bunting differentiate response to signal of different threat value and that the strength of response depends on the age of a male. This study provides experimental evidence that age of receiver affects its response to a territorial intruder. It also demonstrates that observed in many studies variation in response to playback may be an effect of age differences between males, which rarely is controlled.
The rapid development of wind energy may have negative effects on bird populations, including collisions with turbines, displacement due to disturbance or habitat loss, indirect effects of reduced breeding success and barrier effects. This challenging conservation issue has attracted a great deal of interest, but the noise generated by turbines has been largely overlooked. Here, we studied acoustic behaviour of Skylarks Alauda arvensis in relation to wind farm start-up to assess whether a change in song parameters can indicate a deterioration in the acoustic environment. We recorded territorial males displaying close to operating and non-operating turbines and at a control site without turbines. In the following breeding season, we undertook replications at the same sites, except that the non-operating turbines were now in operation. We found that Skylarks displaying at the wind farm were affected by wind turbine noise. Males singing close to operating wind turbines sang higher-frequency songs than males from a control site and those that displayed near non-operating turbines. In addition, an upward frequency shift in songs was observed when non-operating turbines started to operate in the consecutive season. We therefore conclude that the frequency shift observed did not result from turbine presence, but from the noise they started to generate. This shows that a change in song parameters may reliably and within a relatively short time indicate a significant deterioration of the acoustic environment as a consequence of wind farm start-up. This may help conservation biologists to identify species and populations that are particularly susceptible to wind farm noise.
Songbirds learn to sing by imitating their conspecific songs through social learning. It is commonly thought that in species with small repertoires, so‐called crystallization of the song repertoire takes place before the first breeding attempt and afterwards their repertoires remain unchanged. However, the number of studies in which individual song repertoires have been tracked longitudinally under natural conditions is still small. The ortolan bunting (Emberiza hortulana) is a small Eurasian passerine species. Studies on this species have shown that males have small song repertoires (usually 2–3), share the same final phrase within a local dialect area, and their repertoires remain unchanged during their lifetimes. We studied the whole, isolated Norwegian population of this species with 100–150 individually marked males. We compared repertoire sizes and contents using cross‐sectional and longitudinal approaches. We focused on marked males aged 2–10 years and recorded in up to five breeding seasons between 2001 and 2006. There was no local dialect because songs with different final phrases occurred both within and between males. Repertoire size varied between 1 and 24 (4.7 ± 3.4) song types per male. Longitudinal analysis showed an increase in repertoire size in 29% and a decrease in 21% of males. Males whose repertoires remained the same in size between years often substantially changed in contents. New song types appeared in almost 70% of males, and over 30% of males started singing new syllable types after the second calendar year. In almost 50% of males, new song types appeared that were built as new combinations of syllables shown in previous years. In 30% of males, the song complexity increased with age. Simultaneously, over 60% of males selectively ceased singing some song types. We suggest that these repertoire alterations are linked to the isolation and fragmentation of this population, which may affect song learning patterns through increased breeding dispersal and a strongly male‐biased sex ratio. Similar studies from abundant and continuous populations of the species are needed to test this idea.
It is believed that bird song has evolved as a reliable signal of quality of displaying individuals. Recent research has focused on costs of development of complex song. In the present paper we test if the acquired repertoire size is costly to maintain. We compared changes in song structure in male Whitethroats (Sylvia communis) after 48 h exposure to a stressor (5% body mass weight attached to the tail feathers) vs. changes observed within the same time interval in the control group. The strophe length was marginally significantly shorter in the handicapped males comparing to controls. However, the repertoire size (i.e., a measure of diversity of different song elements) remained intact in both groups. We concluded that the song repertoire in Whitethroats is a static secondary sexual trait. A review of literature has revealed no convincing examples of decreasing repertoire size in adult male songbirds. Further research is needed to improve our understanding of evolutionary and proximate mechanisms maintaining the stability of song repertoires.
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