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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Censuses and population estimates compared: Coal Tit Periparus ater und Crested Tit Lophophanes cristatus
Auteurs :	Einhard Bezzel, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (136(1) 2016)
Article en page(s) :	31-41
Résumé :	In 1980-1999, 11,819 Coal Tits Periparus ater and 2,847 Crested Tits Lophophanes cristatus were counted along line transects twice a month each on a southern (3.4 km) and a northern (2.68 km) slope of a valley in the northern Alps of Bavaria in 800-1,000 m a.s.l. On 60.16 ha the average yearly abundance of territory holders in 20 years was estimated with 5 (Coal Tit) and 1 (Crested Tit) per 10 ha. The ratio of monthly medians of individuals between Coal Tit and Crested Tit was 3.5:1 on average with lowest difference in November/December (2.3:1) and the highest in May (6.6:1). In Coal Tits, seasonal dynamics as well as yearly oscillations of numbers were more evident. The pattern of presence in short sections of the transects was highly different between the two species. Assumed that individuals of both species were present all the year round in sections and years with recordings in at least 6 months and/or families with fledglings observed, the monthly detection rate was 0.60 for Coal and 0.39 for Crested Tits. During breeding season the differences of detection rate were high, in autumn and winter considerably lower. In both species the detection rate is positively correlated with the monthly median of individuals, indicating that abundance has a strong effect. If results of counts are corrected with the detection rate the difference in abundance between Coal and Crested Tit from April to July is reduced from 5:1 to 2:1. Crested Tits may be underestimated in many census and monitoring projects presumably over all size classes of area. At least in small areas different species-specific detection rates may be balanced by an adjusted number of checks. Compared with Coal Tits, Crested Tits not displaying a distinct territorial song need one additional check per season at least to detect an identical rate of estimated or expected territories. This difference may depend on size of area and abundance of birds. So in breeding season first territories of Coal Tits were detected earlier than those of Crested Tits, but the total of their territories not. The higher abundance of Coal Tits makes first detection easier but needs more checks to identify all territories. In areas below 100 ha 7-8 checks seem to be a minimum effort to minimize the effects of different detectability of the two species.

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