Abstract
A nestbox breeding population of Pied Flycatchers Ficedula hypoleuca was monitored during 64 years in a mixed coniferous-deciduous forest area near Örebro, South Central Sweden. The population showed a continuous average decline of c. 0.5 pairs per year, from c. 50% to c. 20% occupancy. There was a strong negative correlation between flycatcher numbers and those of other hole-nesters, but it is doubtful whether any causal relationship existed. Mean laying date was 24 May (17 May—3 June) and showed a negative correlation with mean May temperatures, yet no significant trend over the six decades. Mean laying date did, however, show an increased variation during the last 20 years. Mean clutch size varied between 5.76 and 7.08, with a mean of 6.34. It varied more during the last 30 years but without any significant relationship with mean laying date. A mean of 5.96 young fledged from broods that produced at least one fledgling vs 5.34 for all broods; the lower figure was mainly a consequence of nest predation by Pine Marten Martes martes, particularly after the early 1980s.
Highlights
Because Pied Flycatchers Ficedula hypoleuca readily accept nestboxes and are relative insensitive to disturbance, two conditions that make them easy to study, it is hardly surprising that there exists an enormous literature on the species
There was a strong negative correlation (Figure 2, rs = –0.808, P < 0.001) between the proportions of nestboxes occupied by Pied Flycatchers and by other hole-nesters, especially Great Tits Parus major and Blue Tits Cyanistes cyaneus
During the last few decades, a negative trend in Pied Flycatcher population size has been observed in some other Swedish nestbox studies
Summary
Because Pied Flycatchers Ficedula hypoleuca readily accept nestboxes and are relative insensitive to disturbance, two conditions that make them easy to study, it is hardly surprising that there exists an enormous literature on the species. During the first half of the study, mean clutch size remained relatively stable at 6.24 eggs (coefficient of variation, CV = 2.2%), but during the second part it varied considerably more between years (CV = 4.5%; Figure 5).
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