Optimal avian migration: A dynamic model of fuel stores and site use

Weber, Thomas; Ens, Bruno J.; Houston, Alasdair I.

doi:10.1023/a:1006560420310

Cited by 173 publications

(169 citation statements)

References 37 publications

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“…NEAC undertake a long-distance spawning migration (∼800 km each way) (22), starting in early December (23). Like other animal migrations (24)(25)(26), this migration incurs considerable energetic costs (27). An aborted spawning run would cost a female the energy associated with atresia as well as the energy spent on the spawning migration itself.…”

Section: Discussionmentioning

confidence: 99%

Frequent skipped spawning in the world’s largest cod population

Skjæraasen

Nash

Korsbrekke

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Life-history theory suggests that animals may skip reproductive events after initial maturation to maximize lifetime fitness. In iteroparous teleosts, verifying past spawning history is particularly difficult; the degree of skipped spawning at the population level therefore remains unknown. We unequivocally show frequent skipped spawning in Northeast Arctic cod (NEAC) in a massive field and laboratory effort from 2006 to 2008. This was verified by postovulatory follicles in temporarily arrested ovaries close to the putative spawning period. At the population level, "skippers" were estimated to be approximately equally abundant as spawning females in 2008, constituting ∼24% of the females 60-100 cm. These females never truly started vitellogenesis and principally remained on the feeding grounds when spawners migrated southward, avoiding any migration costs. The proximate cause of skipping seems to be insufficient energy to initiate oocyte development, indicating that skipped spawning may partly be a density-dependent response important in population regulation. Our data also indicate more skipping among smaller females and potential tradeoffs between current and future reproductive effort. We propose that skipped spawning is an integral life-history component for NEAC, likely varying annually, and it could therefore be an underlying factor causing some of the currently unexplained large NEAC recruitment variation. The same may hold for other teleosts.codfish | population dynamics | reproductive biology | total egg production | stock reproductive potential P opulation demography changes according to reproduction and mortality. In high latitude marine ectotherms, including teleosts, survival of the youngest age classes varies substantially, resulting in large fluctuations in population size (1). Historic spawning stock biomass (SSB) is used to forecast future fish recruitment, although the amount of unexplained variation indicates that SSB may not accurately reflect offspring production (2, 3). One factor that could significantly impact egg production is skipped spawning-the failure of iteroparous spawners to use each spawning opportunity after sexual maturity sensu (4). For most teleosts this phenomenon and its impact on population demography has received scant attention, but theoretical models indicate that up to 30% of the mature individuals may skip spawning and that it is an adaptive strategy optimizing lifetime fitness (5). To date, skipped spawning has been documented in more than 30 species (4, 6), including freshwater (7), marine (8), and anadromous teleosts (9). It has been documented for fish with both indeterminate and determinate fecundity and sequential hermaphrodites (6) and in species with as diverse life histories as the European horse mackerel Trachurus trachurus (10) and the orange roughy Hoplostethus atlanticus (8). Given the difficulty in conclusively establishing past spawning, reports of skipped spawning in teleosts are commonly anecdotal (4).The major process of energy transfer and oocyte gr...

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Section: Discussionmentioning

confidence: 99%

Frequent skipped spawning in the world’s largest cod population

Skjæraasen

Nash

Korsbrekke

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…In birds having a relatively low energy cost of transport, such as large raptors using thermal soaring, and where refuelling opportunities are limited along the flight route, the best strategy may be not to be wind sensitive and migrate irrespective of wind direction, at least with moderate wind strengths (Thorup et al 2006). Potential sets of rules implementing an overall migration strategy can be evaluated by state-dependent optimization (Weber et al 1998b). Further studies involving the tracking of individual birds are likely to give insights into how rigid/flexible behaviours are during migration and which set of rules are likely to be used in order to achieve an efficient migration strategy.…”

Section: Discussionmentioning

confidence: 99%

Adaptations to migration in birds: behavioural strategies, morphology and scaling effects

Hedenström

2007

Phil. Trans. R. Soc. B

242

217

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The annual life cycle of many birds includes breeding, moult and migration. All these processes are time and energy consuming and the extent of investment in any one may compromise the others. The output from breeding is of course the ultimate goal for all birds, while the investment in moult and migration should be selected so that lifetime fitness is maximized. In particular, long-distance migrants breeding at high latitudes face severe time pressures, which is a probable reason why natural selection has evolved efficient behaviours, physiological and morphological adaptations allowing the maximum possible migration speed. Optimal migration theory commonly assumes time minimization as an overall strategy, but the minimization of energy cost and predation risk may also be involved. Based on these assumptions, it is possible to derive adaptive behaviours such as when and at which fuel load a stopover site should be abandoned. I review some core components of optimal migration theory together with some key predictions. A review of accumulated empirical tests of the departure rule indicates that time minimization is an important component of the overall migration strategy, and hence gives support to the assumption about time-selected migration. I also briefly discuss how the optimal policy may be implemented by the bird by applying a set of simple rules. The time constraints on migrants increase with increasing body size. Some consequences of this are discussed.

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“…The occurrence of such a precise mechanism may or may not be common, but the model of Weber and co-authors (1998a, 1998b, Weber & Hedenström 2000 indicates that its evolutionary appearance is particularly probable over the extensive lowlands of Eastern and Central Europe, in which the convenient stopover sites for such birds as the Robin are both abundant and spatially and temporally stable with respect to food availability and predation pressure. In this entire area there is only a low probability of the occurrence in autumn of the tailwinds that would be favourable to birds migrating to western and south-western wintering grounds (i.e.…”

Section: Discussionmentioning

confidence: 99%