Factors limiting reproductive success in urban Greylag Geese (Anser anser).

In the late eighties, Greylag Geese (Anser anser) started to colonise an urban area previously void of geese in southwestern Germany. Between 2004 and 2020, in a period of steady population increase with subsequent population stagnation, we analysed two measures of reproductive success: (1) the relation between freshly hatched to fledged young for each brood and (2) the probability of a hatchling to survive to fledging. We were able to show that the dispersal of pairs from the nesting site to a different brood rearing area resulted in higher reproductive success. However, the increasing population size of Greylag Geese and the number of breeding pairs of recently immigrated Egyptian Geese (Alopochen aegyptiaca) had a negative impact on reproductive success, indicating density dependence. Our results show that newly established populations in urban settings do not grow indefinitely, which is an important fact that should be taken into account by wildlife managers.

Breeding biology of two wagtail subspecies on Ulleung Island, Korea: Amur Wagtails, Motacilla alba leucopsis and Black-backed Wagtails, M. a. lugens.

There is much controversy over the species and subspecies status of the white wagtail complex, which is further compounded by interbreeding between two subspecies, the Amur Wagtail (Motacilla alba leucopsis) and the Black-backed Wagtail (M. a. lugens). This study presents preliminary information on the breeding biology of both subspecies on Ulleung Island, Korea, over two breeding seasons (2012-2013). Mixed pairs of the two subspecies were common on this island, with almost 50% of all pairs being heterotypic or intermediate pairs; however, assortative mating was still present. Females of both subspecies were more likely to be paired with Amur wagtail males, whereas intermediate females were more likely to be paired with Black-backed Wagtail males. Clutch size, egg size and mass, and reproductive parameters (such as hatching success and nest success) did not significantly differ from each other. However, the mean values were low in intermediate pairs. Our results indicate no reproductive barrier between the two subspecies, but that some post-isolating mechanisms are still in progress.

The influence of sex ratio on the reproduction of pirarucu, Arapaima gigas, in captivity / Influência da proporção sexual na reprodução do pirarucu, Arapaima gigas, em cativeiro

Because sex ratio in the broodstock can influence the reproductive behaviour of a species, the influence of sex ratio on the reproductive success of pirarucu, Arapaima gigas, in captivity was assessed. Pirarucu breeders were stocked in 0.10-0.13 ha earthen ponds at three sex ratios in quadruplicate: one male to one female (1M1F); one male to two females (1M2F); and two males to one female (2M1F). Eight spawning events occurred, seven of them with the 1M1F sex ratio, which was the most successful of the three tested sex ratios.

A proporção sexual de reprodutores pode influenciar o comportamento reprodutivo de uma espécie. Em função disso, avaliou-se o efeito da estocagem de reprodutores em diferentes proporções sexuais no sucesso reprodutivo do pirarucu, Arapaima gigas, em cativeiro. Reprodutores foram estocados em viveiros de 0,10-0,13 ha, distribuídos em três tratamentos (proporções sexuais), com quatro repetições cada: (1M1F) um macho e uma fêmea, (1M2F) um macho e duas fêmeas; e (2M1F) dois machos e uma fêmea. Foram observadas oito desovas, sendo a proporção sexual 1M1F a mais eficiente, apresentando sete desovas. Sugere-se, portanto, que a proporção sexual de um macho para cada fêmea é mais adequada para a reprodução do pirarucu em cativeiro.