1. In field ecological and behavioural studies, it is often necessary to identify specific individuals. In birds, colour rings are frequently used to mark individuals; however, rings are often difficult to observe, especially in small species and dense habitats. Acoustic-based monitoring detecting individuals by their characteristic vocalization is a potentially suitable alternative, but this approach is challenging in species with complex songs. 2. On the example of the Tree Pipit (Anthus trivialis), a small migratory passerine often singing in flight or from perches obscured by foliage, we demonstrate that acoustic monitoring based on the syllable repertoire can be very efficient tool for individual recognition. During a 3-year study, we obtained over 500 recordings from males from one study population (a number of them returning after winter). Males banded with colour rings were repeatedly recorded throughout the seasons, and syllable repertoires were determined from spectrograms for each recording. 3. The repertoire of each unambiguously identified male was distinct and stable within as well as between seasons; and males with similar syllable repertoires differed in syntax. Based on the congruence between identification based solely on spectrogram assessment, and that based on observation of colour rings, we inferred that reliable identification of singing males (including non-ringed ones) was possible in the studied population from assessing a repertoire and song syntax of <5-min recording (containing 20-30 songs). The acoustic-based data: (i) increased the overall estimated number of territorial males at the study locality (from 49 ringed to 61), and improved the estimates of the period of their presence; (ii) revealed dynamic within-season changes in territory occupancy that would otherwise be missed; and (iii) allowed identification of returning birds (including nonringed ones and those actively avoiding approaching humans). 4. Our results suggest that some commonly used methods may substantially underestimate return rates of migratory bird species. Individual acoustic monitoring should be applicable on various bird species with complex song and stable repertoires, and may be particularly useful for those living in dense habitat or sensitive to handling.

Habitat preferences of the tree pipit (Anthus trivialis) and the meadow pipit (A. pratensis; Passeriformes: Motacillidae) were observed during the years 1998-1999 at three localities in the Czech Republic; two with one pipit species only, and a third with both species present. We investigated one of the possible mechanisms allowing syntopic coexistence-different habitat selection. We characterised territories of each pipit pair by the habitats present in the territory (defined by dominant plant composition) and by quantitative parameters (territory size, height and density of the vegetation, number of look-outs of different height categories, and proportion of wet ground). Tree pipits preferred significantly higher vegetation of lower density than meadow pipits, and there was generally a higher number of high look-outs in their territories. However, in some of the preferred territories at the allopatric locality of the tree pipit, steep hill slopes could well substitute for higher look-outs, which were almost absent. The two pipit species at the sympatric locality occupied very different habitats, which was also reflected in quantitative parameters of their territories. The available data of pipit habitat at different European localities show that the two species can occupy a much wider range of habitats. The habitat separation in sympatry might therefore be one of the mechanisms allowing syntopic coexistence of both species.

Transmitting information about singer's quality is an important function of song in many bird species, and this information should be useful in territorial interactions. Fast trills, being physically demanding song structures, are particularly suitable candidates for signalling of quality or aggressive motivation. We have evaluated trill characteristics in songs within a population of the Tree Pipit, a common European songbird with no sexual dimorphism, in which song apparently plays a key role in territory defence as well as mate choice. Two types of relatively fast trills (each of them in multiple variants differing in complexity) were commonly observed in repertoires of Tree Pipit males. Trill rates significantly differed among individuals, suggesting that these song structures may carry information about male quality in this species. We tested by playback experiments whether both trill types are used in territorial encounters. Only one of the trill types was sung by males in response to playback, regardless on the trill type played to them. In an immediate response to playback, they increased the frequency of use of this trill, and also significantly increased the trill rate in comparison with spontaneous songs. This confirmed field observations, suggesting that this trill is important in male-male interactions. On the contrary, the use of the fastest, apparently more demanding, trill type actually decreased after the simulated territorial intrusion. We hypothesize that the latter one is more directed towards females, and that while performance of both trill types may reflect male quality, they are primarily used in different contexts.Ethology 120 (2014) 586-597

Ringing is the most common technique used for individual marking of passerine birds, informing understanding of many aspects of their behaviour and ecology. Birds caught for ringing may also be substantially handled before release (e.g. to obtain biometric data, blood or feather samples), and all such procedures may affect the subsequent behaviour of a captured individual. Previous field studies that have assessed the potential effects of capturing and handling birds have nevertheless, to date, lacked an entirely independent unhandled control. In this study, we used individual acoustic monitoring to compare the apparent survival and re-encounter probabilities of male tree pipits Anthus trivialis that were captured with mist nets and intensively handled (measured, blood-sampled and ringed) with those of a control group of unhandled birds tracked solely by their vocalization. There were no differences between handled and unhandled birds in apparent survival rates, either in simple annual estimates, or in jointly estimated within-and between-breeding season survival estimates. Re-encounter probabilities in the latter analysis peaked at the start of the breeding season, when song activity would be expected to be greatest, but were higher for handled than unhandled birds in mid-to late May. Apart from demonstrating that tree pipits were not affected in the long-term by capture and associated handling, our study confirms that individual acoustic monitoring is a valuable non-intrusive method for long-term monitoring studies.

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