Abstract:

I studied alliance of breeding birds between 1982-1990 in three different marshes of Hungary. I found several co-nestings, that is, when a small bird nested under the nest of a large bird (usually a heron). From the total 803 heron nests there were only 42 cases, when a nest of a small bird was found under the big nest. There were great differences between the observed number of co-nestings in the three study areas (37, 5, 0, respectively), which can be attributed to the differences in the vegetation structure. Tb us one reason for co-nesting may be the provision of well-hidden nesting place. Another explanation may be the alliance, that is an increase of vigilance.