Korner-Nievergelt F.,Swiss Ornithol Institute |
Sauter A.,Swiss Ornithol Institute |
Atkinson P.W.,British Trust for Ornithol. |
Guelat J.,Swiss Ornithol Institute |
And 8 more authors.
Journal of Avian Biology | Year: 2010
Ring re-encounter data, in particular ring recoveries, have made a large contribution to our understanding of bird movements. However, almost every study based on ring re-encounter data has struggled with the bias caused by unequal observer distribution. Re-encounter probabilities are strongly heterogeneous in space and over time. If this heterogeneity can be measured or at least controlled for, the enormous number of ring re-encounter data collected can be used effectively to answer many questions. Here, we review four different approaches to account for heterogeneity in observer distribution in spatial analyses of ring re-encounter data. The first approach is to measure re-encounter probability directly. We suggest that variation in ring re-encounter probability could be estimated by combining data whose re-encounter probabilities are close to one (radio or satellite telemetry) with data whose re-encounter probabilities are low (ring re-encounter data). The second approach is to measure the spatial variation in re-encounter probabilities using environmental covariates. It should be possible to identify powerful predictors for ring re-encounter probabilities. A third approach consists of the comparison of the actual observations with all possible observations using randomization techniques. We encourage combining such randomisations with ring re-encounter models that we discuss as a fourth approach. Ring re-encounter models are based on the comparison of groups with equal re-encounter probabilities. Together these four approaches could improve our understanding of bird movements considerably. We discuss their advantages and limitations and give directions for future research. © 2010 The Authors. Journal compilation © 2010 Journal of Avian Biology.
Reers H.,Max Planck Institute for Ornithology (Seewiesen) |
Reers H.,Dalhousie University |
Leonard M.L.,Dalhousie University |
Horn A.G.,Dalhousie University |
And 2 more authors.
Journal of Avian Biology | Year: 2014
Acoustic signatures are common components of avian vocalizations and are important for the recognition of individuals and groups. The proximate mechanisms by which these signatures develop are poorly understood, however. The development of acoustic signatures in nestling birds is of particular interest, because high rates of extra-pair paternity or egg dumping can cause nestlings to be unrelated to at least one of the adults that are caring for them. In such cases, nestlings might conceal their genetic origins, by developing acoustic signatures through environmental rather than genetic mechanisms. In a cross-fostering experiment with tree swallows Tachycineta bicolor, we investigated whether brood signatures of nestlings that were about to fledge were attributable to their genetic/maternal origins or to their rearing environment. We found that the calls of cross-fostered nestlings did not vary based on their genetic/maternal origin, but did show some variation based on their rearing environment. Control nestlings that were not swapped, however, showed stronger brood signatures than either experimental group, suggesting that acoustic signatures develop through an interaction between rearing environment and genetic/maternal effects. © 2014 The Authors.
Gruebler M.U.,Swiss Ornithol Institute |
Gruebler M.U.,University of Zürich |
Naef-Daenzer B.,Swiss Ornithol Institute
Journal of Avian Biology | Year: 2010
In seasonal environments, avian reproductive performance almost generally declines in the course of the season. Quantifying the associated fitness consequences of timing of breeding, i.e. of date-related factors, is important for understanding the evolution of temporal patterns in avian life-histories and for predicting consequences of climate change. The seasonal decline can also be caused by an effect of parental quality: individuals with high phenotypic quality may breed early. The results of existing experimental studies investigating whether date or quality effects cause the seasonal decline are inconsistent, indicating that both mechanisms might be involved. However, it remains unclear to what extent the confounding effect of quality occurs and what the fitness consequences of timing per se over a whole breeding episode are. In a cross-fostering experiment using the barn swallows' second broods we evaluated the causes for the seasonal decline in reproductive performance for three distinct periods of a reproductive attempt, the early nestling period, the late nestling period and the post-fledging period, and we assessed the overall fitness consequences of timing per se. A seasonal decline in juvenile feather growth rate was mainly due to date effects in the late nestling period, although we determined quality effects during early nestling development. Date effects on survival were present in the post-fledging period, but not in the nestling period. The decline in feather length due to date effects in the nestling period accounted for 9% of the seasonal decline in post-fledging survival, whereas date effects arising only in the post-fledging period caused 91% of the decline. These results suggest that date effects increase in the course of a reproductive episode. Thus, the benefits of an early timing of breeding can be quantified only when considering also the post-fledging period. We suggest that the timing of breeding evolved through a trade-off between date-related benefits and quality-related costs of early breeding. © 2010 The Authors.