Dynamics Of Number Of Grey Herons (ardea Cinerea L.) Colony In The Upper Course Of Zaporozhye (dneprovskoye) Reservoir

Abstract

Ð?. V. Vovk

The research was performed in the area of natural reserve "Dneprovsko-Orelsky" and its adjacent territory – the island Pogorely. We discovered the changes of number of grey heron in colonial settlements, determined the principal factors influencing the formation of spatial structure of island bird communities. The analysis of nest distribution towards tree breeding biotopes was performed and stability of spatial structure of bird colonies was proved. We were tracking the number dynamics of pioneer colony and revealed the principal ecological and anthropogenic factors influencing the fluctuation of its abundance. There was some annual variability in the distribution of nests. In 2007, an average we count three nests per one tree. In 2008 and 2009 we registered the increase of this indicator - it was 5 and 8 nests per tree respectively. This was followed by stabilization of the average density until 6 nests per tree. The analysis of the distribution of the nests on the trees for the entire period of observation was very informative. The closest statistical distribution was the theoretical Poisson distribution. Deviations from the theoretical distribution can highlight the ecological nature of the phenomenon which was observed. Thus, the analysis of the histogram indicates that the number of nests was 4-7 per tree and this was much less than might be expected theoretically for a Poisson distribution. In contrast, the density of 23-31 nest per tree exceeds the level that can be expected based on the assumption of completely random (neutral) pattern of spatial organization of bird settlement. The advantage of dense groupings of the nests over groups with moderate density indicates that such settlement quite confidently could be attributed to the colonial type. Analysis of the nest distribution pattern towards specific tree proved certain stability of the spatial structure of colonial bird settlement

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