Abstract:

We studied the pair-formation of the Bearded Tit in the year of hatching and the permanence of these pair bonds at the Lake Luda¹ko (Yugoslavia) between 1989-1999. The study period ranged each year from mid-July until the beginning of September. During the project 3279 Bearded Tits were ringed and 1262 recaptured. Two individuals were treated as pairs if matched one of the following criteria: (1) caught in the same or neighbouring net; (2) caught during the same, previous or subsequent mist-net control occasion; or (3) caught at least twice together, on the same day. These restrictions were fulfilled by 36 pairs: 33 pairs were captured twice and 3 three times. The proportion of male / female pairs was 89%, while 75% of them was formed by two juvenile birds. On the basis of the high proportion of juvenile pairs we suggest that pairs formed in the year of hatching. Every pair that was marked together and controlled during the following years consisted of a male and a female, which suggested that relations were permanent. The strength of relation between pair-forming individuals was tested with Fisher exact test, which showed significant associatedness. The sexual distribution of different pair-types was analyzed using
2 test. The number of heterosexual pairs was significantly higher than expected. Families tended to keep together after the fledging of chicks, and in the beginning of the study period birds moved in flocks. These groups broke into "engaged couples" by the end of July - beginning of August, which is very likely the period of pair-formation. The activity of birds decreased by mid August, caused by the intensive complete moult. After two-weeks of low activity, individuals of different age-groups built up mixed flocks. Associated pairs could be detected in these groups, that begun their regular roaming in late autumn.