Nest predation is an essential factor affecting bird population density, reproductive ecology and life cycle. However, there are still contradictory results about how nest predation pressure changes with urbanization. One of the reasons for the controversy is that previous studies often use artificial nests to investigate nest predation, but the result of artificial nests is often biased and contrary to that of natural nests. Therefore, it is important to perform nest predation experiments simultaneously with both natural and artificial nests. In this study, we examined the change of nest predation pressure on the Chinese Bulbul (Pycnonotus sinensis) along the urbanization gradient in Hangzhou, China. We detected 148 natural nests of Chinese Bulbuls and continuously monitored them in two continuous breeding seasons from 2012 to 2013. After the breeding season, we placed artificial eggs in natural nests of Chinese Bulbuls to investigate the changes in nest predation pressure and used infrared cameras to record the predators. We then calculated the urbanization synthetic index (USI) as the measure of the degree of urbanization and examined its relationship with nest predation pressure. We found that no matter whether natural nests or artificial eggs were used, the nest predation pressure always decreased significantly with the degree of urbanization. The average height of shrubs within 10 m of the nest differed significantly between the predated and unpredated nests, which also affected the risk of nest predation. Our study highlights the importance of using natural and artificial nests simultaneously to conduct nest predation experiments, which can reduce the bias or errors caused by only using artificial nests. We also recommend the use of infrared cameras in future nest predation studies, which has obvious advantages in monitoring and identifying potential predators.
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Open Access
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Nest sanitation behavior is one of the most important means to ensure high reproductive efficiency. In avian brood parasitism, nest sanitation behavior may be a pre-adaptation of host birds that allows them to identify the parasitic eggs, so that egg discrimination behavior may have evolved from nest sanitation behavior. However, whether nest sanitation behavior could improve egg rejection in cuckoo hosts was inconclusive.
In this study, we investigated the relationship between nest sanitation and egg discrimination behavior in a potential cuckoo host, the Brown-breasted Bulbul (Pycnonotus xanthorrhous) with two experimental groups. In the first group, we added a blue, non-mimetic egg to the nest of the host, while in the second group we added a blue, non-mimetic egg and a peanut half-shell.
The results showed that in the first group, the probability of rejecting the non-mimetic eggs was 53.8% (n = 26 nests). In comparison, all of the Brown-breasted Bulbuls in the second group were able to rapidly remove the peanut shells from the nest, but only 52.6% (n = 19 nests) rejected the non-mimetic eggs. The rejection rates of the non-mimetic eggs in both experimental groups were not significantly different.
Our study indicated that nest sanitation behavior of Brown-breasted Bulbuls did not influence their egg recognition and that egg discrimination ability of Brown-breasted Bulbuls was not directly related to nest sanitation behavior.
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