Ardea Official journal of the Netherlands Ornithologists' Union |
García-Navas V. & Sanz J.J. (2012) Yearly and seasonal variation of breeding parameters in a declining multi-brooded passerine, the Tree Sparrow. ARDEA 100 (1): 79-88 |
Over a five-year period we monitored breeding parameters in a colony of Tree Sparrows Passer montanus in central Spain. This multi-brooded species can raise one to three broods per season. In this study, we analyzed inter-brood variation in reproductive success to infer the existence of seasonal patterns. We also explored inter-annual variation of life-history traits, which is of particular interest in a declining species like the Tree Sparrow. In agreement with our expectation of a multi-brooded species, clutch size showed a quadratic relationship with laying date. We found that the inter-brood interval varied significantly depending on the number of breeding attempts, which suggests that the species may engage in time-saving behaviours as reported for other multi-brooded passerines. Nestlings from second broods fledged in better condition than nestlings from first and third broods. Fewer fledglings were produced in third broods than in preceding breeding attempts. The reproductive output of third broods varied to a large extent among years, whereas inter-annual variation was much less marked in first and second broods. Over the years, we also detected a decrease in nestling size (tarsus and wing length), which was consistent among breeding attempts. Finally, the productivity of the colony remained fairly stable over the study period. This pattern contrasts with negative population trends detected by national monitoring programmes. The proximity of wetland habitats in the surroundings of our colony – essential for adequate invertebrates for the chicks – is suggested as a main reason for this difference. |