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Brood overlapping is a breeding strategy that aims at shortening the time between successive broods. Most typically, each brood is raised in separate nest and parents share care between broods. If successive overlapping broods are located in the same nest, the second brood is usually initiated after nestlings from the previous brood have left the nest. The cases in which a female lays eggs in the same nest but before the nestlings from the previous brood have fledged (hereafter, Single Nest Brood Overlapping, SNBO) are rare and seldom studied. Based on a literature research, we revise data on SNBO occurrence. To date, about 37 cases of SNBO have been recorded in eight bird species and occurs mainly nest box breeders. Moreover, we surveyed SNBO in a wild-living passerine, Great Tit (Parus major). We found evidence of SNBO in 10.1% of the 69 first broods that we monitored using camera traps installed inside nest boxes. Females started the second brood when first brood nestlings were 17-19 days old, up to 6 days prior to fledging. This type of brood overlap occurred more often in nests that had smaller initial number of fledglings. The timing of the first brood, the clutch size and duration of the nestling phase had no significant effect on SNBO occurrence. We discuss some potential causes and fitness consequences of this unusual breeding strategy.

Nest site availability plays an important role in the ecology of the birds inhabiting intensive agricultural landscapes. The removal of trees and snags due to logging is one of the main threats and the cause of the observed decline in many birds living in an agricultural landscape. When nests are lost, nesting passerines typically rebuild them for a new clutch. Additionally, relocating nests after a brood loss is a prevalent strategy used to avoid predators and brood parasites. Such a strategy is common to the Red-backed Shrike, which builds successive nests for each brood. Interestingly, clutch replacement may occur in unusual forms. This study describe three cases of Song Thrush nests reused by Red-backed Shrikes during one breeding season. The time and energy-saving behaviour or possible deterrence of nest parasitism could explain why the nests have been reused. However, due to the limited observations as compared to the total number of nests, further research is necessary to clarify this phenomenon.

Normal gonad development assures the fertility of the individual. The properly functioning gonads must contain a sufficient number of the viable germ cells, possess a correct architecture and tissue structure, and assure the proper hormonal regulation. This is achieved by the interplay between the germ cells and different types of somatic cells. N-cadherin coded by the Cdh2 gene plays a critical role in this interplay. To gain an insight into the role of N-cadherin in the development of mouse gonads, we used the Cre-loxP system to knock out N-cadherin separately in two cell lines: the SF1+ somatic cells and the OCT4+ germ cells. We observed that N-cadherin plays a key role in the survival of both female and male germ cells. However, the N-cadherin is not necessary for the differentiation of the Sertoli cells or the initiation of the formation of testis cords or ovigerous cords. In the later stages of gonad development, N-cadherin is important for the maintenance of testis cord structure and is required for the formation of steroidogenic cells. In the ovaries, N-cadherin is necessary for the formation of the ovarian follicles. These results indicate that N-cadherin plays a major role in gonad differentiation, structuralization, and function.