Abstract
The breeding success of blackbirds was investigated in April and June 2008 and 2009 in the Botanical Garden of the University of Pecs, with a total of 50 artificial nests at each of the four sessions (with 1 quail egg and 1 plasticine egg placed in every nest). In all four study periods of the two years, 2 nests (4%) were destroyed by predators. Six nests (12%, of the nests) were not discovered in either of the cases. The survival probability of artificial nests was greater in April than in June (both years), but the difference was significant only in 2008. Nests placed into a curtain of ivy (Hedera helix) on a wall were located higher up than those in bushes, yet their predation rates were quite similar. The predation values of quail vs. plasticine eggs did not differ in 2008. In the year 2009, however, significantly more quail eggs were discovered (mostly removed), than plasticine eggs. Marks that were left on plasticine eggs originated mostly from small mammals and small-bodied birds, but the disappearance of a large number of quail and plasticine eggs was probably caused by larger birds, primarily jays.
Highlights
Being one of the most common city birds, blackbirds (Turdus merula) raise two or even three clutches a year (Ludvig et al, 1995, Cramp, 1998)
Blackbird nests have increased survival probability which is due to the fact that predators at this stage have not shifted to nest predation as a resource (Ludvig et al, 1995)
Our results show that the survival probabilities of artificial nests built in April are greater than those of nests built in June
Summary
Being one of the most common city birds, blackbirds (Turdus merula) raise two or even three clutches a year (Ludvig et al, 1995, Cramp, 1998). As revealed by our investigations performed in 20062007, altogether 43 bird species occurred in the cca. 18 species were nesting in the area, and the most frequent one was the blackbird. It may be that the increase observed in May was partly caused by young birds from the first clutch, but why did such an increase not occur after the second clutch as well? As the breeding season proceeds, predation pressure on blackbirds generally increases (Ludvig et al, 1995), which may be associated with the degree of nest concealment and predator activity (Wysocki, 2005). Artificial nest experiments (Bayne and Hobson, 1999, Major and Kendal, 1996) carried out to investigate predation rates and to identify potential predators are useful because such experiments are unobtrusive to the real nests and the incubating birds
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