Extreme migration and the individual quality spectrum
Conklin, J.R.; Senner, N.R.; Battley, P.F.; Piersma, T. (2017). Extreme migration and the individual quality spectrum. J. Avian Biol. 48(1): 19–36. dx.doi.org/10.1111/jav.01316
In: Journal of Avian Biology. Munksgaard: Copenhagen. ISSN 0908-8857; e-ISSN 1600-048X, more
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| Authors | | Top |
- Conklin, J.R.
- Senner, N.R.
- Battley, P.F.
- Piersma, T., more
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| Abstract |
Costsof migration, in terms of time, energy, and mortality risk, have a strong theoretical and empirical foundation in thestudy of birds. We expect these costs to be most severe for extreme long-distance migratory landbirds, whose demandingannual routines (e.g. non-stop flights 8000 km and return journeys 30 000 km) may approach their maximumphysiological capabilities. To explore whether this is true, we review evidence in long-jump migratory shorebirds(Scolopacidae), focusing most on the prototypical example, the Alaska-breeding bar-tailed godwit Limosa lapponicabaueri. Contrary to expectations, these and similar birds demonstrate high adult survival, little evidence for elevatedmortality during migration, no apparent minimisation of non-stop flight distances, and low inter- and intra-individualvariation in migration performance. Two key aspects of extreme migrants may explain these findings: 1) a counterintuitivelyconservative annual-cycle strategy, which minimises risks and enables dissipation of carry-over effects beforefitness consequences arise; and 2) selection pressure during early life, which quickly removes low-performing individualsfrom the population. We hypothesise that these two factors, applicable to extreme strategies in a wide range of taxa, act totruncate the range of individual quality in a population, and decrease the prevalence and detectability of carry-over effects.Testing these hypotheses is challenging, as it requires comparative studies of demography and individual quality spectraalong a continuum of extremeness. However, it has important potential implications for interpreting individual variation,designing studies of cross-seasonal interactions or costs of migration, and recognising early-warning signs of populationdecline. For example, the most extreme shorebird migrations rely on abundant but difficult-to-access resources; the highminimum individual performance required for survival predicts that degradation of these resource hot-spots will propelrapid population collapse, rather than incremental declines in condition or performance. Therefore, in extreme migrants,we may paradoxically view populations as operating close to the edge, even while individuals are not.‘ |
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