McDonald Birgitte I.

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McDonald
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Birgitte I.
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  • Article
    Seals map bathymetry of the Antarctic continental shelf
    (American Geophysical Union, 2010-11-03) Padman, Laurie ; Costa, Daniel P. ; Bolmer, S. Thompson ; Goebel, Michael E. ; Huckstadt, Luis A. ; Jenkins, Adrian ; McDonald, Birgitte I. ; Shoosmith, Deborah R.
    We demonstrate the first use of marine mammal dive-depth data to improve maps of bathymetry in poorly sampled regions of the continental shelf. A group of 57 instrumented elephant seals made on the order of 2 × 105 dives over and near the continental shelf on the western side of the Antarctic Peninsula during five seasons, 2005–2009. Maximum dive depth exceeded 2000 m. For dives made near existing ship tracks with measured water depths H<700 m, ∼30% of dive depths were to the seabed, consistent with expected benthic foraging behavior. By identifying the deepest of multiple dives within small areas as a dive to the seabed, we have developed a map of seal-derived bathymetry. Our map fills in several regions for which trackline data are sparse, significantly improving delineation of troughs crossing the continental shelf of the southern Bellingshausen Sea.
  • Article
    Low hunting costs in an expensive marine mammal predator
    (American Association for the Advancement of Science, 2024-05-15) Rojano-Donate, Laia ; Teilmann, Jonas ; Wisniewska, Danuta M. ; Jensen, Frants H. ; Siebert, Ursula ; McDonald, Birgitte I. ; Elmegaard, Siri L. ; Sveegaard, Signe ; Dietz, Rune ; Johnson, Mark ; Madsen, Peter T.
    Many large terrestrial mammalian predators use energy-intensive, high-risk, high-gain strategies to pursue large, high-quality prey. However, similar-sized marine mammal predators with even higher field metabolic rates (FMRs) consistently target prey three to six orders of magnitude smaller than themselves. Here, we address the question of how these active and expensive marine mammal predators can gain sufficient energy from consistently targeting small prey during breath-hold dives. Using harbor porpoises as model organisms, we show that hunting small aquatic prey is energetically cheap (<20% increase in FMR) for these marine predators, but it requires them to spend a large proportion (>60%) of time foraging. We conclude that this grazing foraging strategy on small prey is viable for marine mammal predators despite their high FMR because they can hunt near continuously at low marginal expense. Consequently, cessation of foraging due to human disturbance comes at a high cost, as porpoises must maintain their high thermoregulation costs with a reduced energy intake.