Improved estimates of certainty in stable-isotope-based methods for tracking migratory animals

Ecological Applications 01/2008; 18:549-559. DOI: 10.1890/07-0058.1
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    ABSTRACT: Insect migration may involve movements over multiple breeding generations at continental scales, resulting in formidable challenges to their conservation and management. Using distribution models generated from citizen scientist occurrence data and stable-carbon and -hydrogen isotope measurements, we tracked multi-generational colonization of the breeding grounds of monarch butterflies (Danaus plexippus) in eastern North America. We found that monarch breeding occurrence was best modelled with geographical and climatic variables resulting in an annual breeding distribution of greater than 12 million km(2) that encompassed 99% occurrence probability. Combining occurrence models with stable isotope measurements to estimate natal origin, we show that butterflies which overwintered in Mexico came from a wide breeding distribution, including southern portions of the range. There was a clear northward progression of monarchs over successive generations from May until August when reproductive butterflies began to change direction and moved south. Fifth-generation individuals breeding in Texas in the late summer/autumn tended to originate from northern breeding areas rather than regions further south. Although the Midwest was the most productive area during the breeding season, monarchs that re-colonized the Midwest were produced largely in Texas, suggesting that conserving breeding habitat in the Midwest alone is insufficient to ensure long-term persistence of the monarch butterfly population in eastern North America.
    Proceedings of the Royal Society B: Biological Sciences 01/2013; 280(1768):20131087. · 5.68 Impact Factor
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    ABSTRACT: Conflict between cormorants (Phalacrocorax spp.) and humans over fisheries is currently one of the most widespread wildlife management issues in the world. Cormorant impact assessments typically assume a single source of prey near the breeding colony. However, cormorants can fly long distances (>20 km), resulting in fish removal from multiple areas. Knowledge of the source of cormorant prey is critical for fisheries impact assessments. Carbon and nitrogen stable isotopes values from fish in double-crested cormorant (Phalacrocorax auritus) regurgitations revealed several prey sources for breeding birds in north-central Saskatchewan, Canada. Cormorants also switched feeding locations on a daily and seasonal basis. Foraging patterns inferred by stable isotope analysis closely paralleled observations of relative cormorant densities on different lakes. Up to 80% of prey came from areas well removed from the breeding colony lake (≤30 km). Cormorant foraging ecology can be complex and may be driven by factors independent of breeding colony site selection. The approach of estimating biomass removal from breeding colony lakes as the guideline for management decisions may be invalid in many locations.
    Canadian Journal of Fisheries and Aquatic Sciences 01/2013; 70(2):271-279. · 2.32 Impact Factor
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May 22, 2014