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Sexual conflict has long been perceived as a solid background for the evolution of parental care. Recent studies, however, highlight the importance of cooperation between the parents, especially in socially monogamous systems. Here, we examined parental performance of a small monogamous passerine with bi-parental care, the Eurasian Reed Warbler (Acrocephalus scirpaceus, RW), looking at the issue from the perspective of parents' cooperation. Using accurate and non-invasive video data on parent chick provisioning from 78 nests varying in brood size, we found some evidence of parents cooperation: both parents similarly adjusted their feeding rate to brood size, and the higher was their both contribution, the better was chicks condition (expressed by defecation rate). However, contrary to our expectations (based on premises from similar studies on other bird species) we did not find evidence for frequent and active synchronisation of nest visits. Importantly, we found a negative relationship between synchronisation level and chick body condition, suggesting that synchronisation may actually not be that beneficial in the study system. The results are surprising and highlight the importance of studying various species to understand mechanisms behind cooperation of partners in the bi-parental care system. Significance statement: Biparental care has long been viewed in the context of conflict between the breeding partners, and only recently they are considered cooperating agents caring together for the common offspring. Nevertheless, studies applying such a perspective are still scarce and there is a pressing need to test different species. Using video data on chick provisioning by Reed Warbler parents, we found evidence of partner cooperation: both parents adjusted their feeding rate to the number of nestlings, and the higher was their joint contribution, the better was offspring condition. Parents did not synchronise their nest visits more compared to randomly generated visits, but we found that synchronisation level negatively affected chick condition. Our results highlight the need to consider various species to fully understand mechanisms behind cooperation of breeding partners. [ABSTRACT FROM AUTHOR]

Bird nests can provide habitats for various invertebrates, including ectoparasites, scavengers, and predators. Records of ants associating with active bird nests mostly involve the insects searching for food, with some exceptional records of ants raising their broods (eggs, larvae or pupae) within songbird nests in nest-boxes or tree cavities. We present data for a previously undocumented, but apparently regular, occurrence of ants and their broods within the active nests of a songbird, the wood warbler Phylloscopus sibilatrix (Bechstein, 1793), which builds domed nests on the ground in European forests. Systematic recording found ants, mostly Myrmica ruginodis Nylander, 1846, in 43% of 80 wood warbler nests in the primary forest of Białowieża National Park (Poland) during the springs of 2016-2017, including ant broods in 30%. Ad hoc records from this site in 2004-2015 found ants in a further 29% of 163 nests, including broods in 20%, indicating a regular association. However, examination of 37 nests from secondary forest in Switzerland and Great Britain founds ants in only 14%, and broods in just 5%. We discuss the potential drivers and mechanisms of the observed association between breeding wood warblers and ants, including the apparent difference in frequency between the primary and secondary forests. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Ornithology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Ornithology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)