Spatio-temporal variation in nestling sex ratio among the Black Stork Ciconia nigra populations across Europe

Abstract

Sex ratio is an indicator of population health as unexpected biases may indicate potential threats. We studied nestling sex ratio in Black Stork Ciconia nigra populations in order to check potential biases and differences along east-west and north-south gradient across its distribution range in Europe. We also studied variation between years, and checked potential correlations with weather variables. The overall sex ratio of nestlings in Europe was nearly equal with a non-significant deficiency (47.1 %) of males, the larger sex. Although yearly fluctuations in sex ratio were detected, no significant effect of the year alone was found, only simultaneously with population and brood size. There was a tendency to have a higher proportion of female nestlings in larger broods, but the pattern was probably scattered by the effect of reduction of largest broods. Compared to Western and Eastern Europe, a significant deficiency of male nestlings was found in Central Europe (Poland), whereas no differences were found along the north-south gradient. We did not find any effect of temperature, but rainfall during the incubation period was negatively correlated with the proportion of male nestlings in Central (Poland) and Western Europe (France) whereas in North-Eastern Europe (Latvia) the same effect of the precipitation in pre-breeding period was found.

Solitude at periphery: lack of partners limits reproduction of the Black Stork (Ciconia nigra) at the margin of the distribution range

“…This is consistent with what we observed in our study. We have shown earlier that sex ratio of Black Stork nestlings is balanced in most of Europe, including Es-tonia (Konovalov et al 2015). Hence, if the bias exists, it must develop after fledging either via sexspecific dispersal or mortality (Gowaty 1993, Székely et al 2014.…”

Low juvenile survival threatens the Black Stork Ciconia nigra in northern Europe

“…A subsample of 175 birds from Estonia and Latvia were sexed by DNA analysis (Fridolfsson and Ellegren 1999). This subsample (79 females and 96 males), supplemented with marked but unsexed and later unseen birds (assuming an equal sex ratio in the Baltic region; Konovalov et al 2015), was used for detecting sex-specific biases in survival.…”

The Impact of Different Management Scenarios on the Availability of Potential Forest Habitats for Wildlife on a Landscape Level: The Case of the Black Stork Ciconia nigra (Linnaeus, 1758)

“…In Western Europe adaptation to human activity has been noted, in contrast to a decline in population and continual avoidance of humans in the eastern part of the continent. However, most European black storks are still found in Eastern Europe [52,53]. In Estonia, at the northern extreme of the black stork range, the mean distances from the forest edge, buildings, and roads are 274 ± 60 m (±95% confidence intervals), 621 ± 99 m, and 1205 ± 183 m, respectively [25].…”