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Climate change is affecting many living organisms; however, the responses of many of them remain unknown. In this paper, we present the results regarding the response of a bird species from the rallid family to the increased temperatures during the breeding season. We analysed the breeding data of Eurasian Coots nesting during 30 seasons between 1972 and 2019. During the study period, mean temperatures in April, the month when Coots start nesting, increased by 3.5 °C, and in months corresponding with the species breeding season by 2.6 °C. Breeding Coots advanced their earliest and median laying dates across the study period; however, the duration of their breeding season remained unchanged. We did not detect any significant temporal changes in clutch size, but clutches have become much more variable in size throughout the study period. Nest failures and production of offspring per nest did not change over the study period; however, the production of young per successful nest significantly declined. It is likely that this decline is the effect of mismatch between the period of food abundance (dipterans collected from water), and hatchling emergence, which is advanced due to change in climate. Future studies investigating the occurrence of dipteran resources at water bodies are needed to test this hypothesis.

Decades of studies have revealed the striking adaptations of avian brood parasites for their unique reproductive lifestyle. Several have reported that adult brood parasites sometimes kill host nestlings, although the reasons for this behaviour remain unclear. Using continuous video-recording and camera traps, we observed the same behaviour in the common cuckoo Cuculus canorus, showing that both host and parasite nestlings can be killed. The latter has never previously been observed in cuckoos. Here, we review this phenomenon and discuss possible explanations.

When production costs or fitness returns vary between sons and daughters, selection is expected to favor females that adjust sex ratios accordingly. However, to what extent birds can do so remains debatable. Here we analyze the secondary offspring sex ratios in Marsh Tits Poecile palustris breeding in the primeval, strictly protected, part of Białowieża National Park (north-eastern Poland). We collected data on parent birds (age), their breeding performance (laying dates, clutch size, nesting success), and the offspring sex ratio in two types of old growth habitats over three years. The individual broods varied from all male to all female, but no significant deviation from parity was detected at the population level. The inter-brood variation could be accounted for neither by environmental (season, habitat) nor parental (female age, laying dates, clutch size, and brood size) variables analyzed. The primary sex ratios (at laying) did not differ from the secondary (brood) sex ratios. Thus, there was no indication of post-hatching sex ratio adjustments, either. Together, our results do not support the hypothesis of adaptive sex ratio adjustments in the studied Marsh Tit population. We suggest that possible fitness benefits could be insufficient to exceed the costs conferred by sex ratio manipulation in this species.

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