Mass dynamics of wintering Pacific Black Brant: body, adipose tissue, organ, and muscle masses vary with location

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Abstract:

We compared body size and mass of the whole body, organs, adipose tissue, and muscles of adult Pacific Black Brant (Branta bernicla nigricans (Lawrence, 1846)) collected concurrently in Alaska and Baja California during the fall, winter, and spring of 2002–2003. Head and tarsal lengths of males were similar between sites and slightly larger for females in Alaska than in Baja California. Brant appear to operate under similar physiological bounds, but patterns of nutrient allocation differ between sites. Birds wintering in Alaska lost similar amounts of adipose tissue during early winter as birds in Baja California gained during late winter before migration. Masses of the body, adipose tissue, and flight muscles during mid-winter were similar between sites. Seasonal adipose tissue deposition may, therefore, equally favor winter residency or long-distance migration. Gonad and liver masses increased in late winter for birds in Alaska but not for those in Baja California, suggesting birds wintering in Baja may delay reproductive development in favor of allocating reserves needed for migration. Phenotypic flexibility allows Brant to use widely divergent wintering sites. The wintering location of Brant likely depends more upon changes in environmental conditions and food availability, than upon physiological differences between the two wintering populations.

Nous comparons les tailles et les masses du corps entier, des organes, du tissus adipeux et des muscles chez des bernaches cravants du Pacifique (Branta bernicla nigricans (Lawrence, 1846)) récoltées à la même époque en Alaska et en Basse-Californie, en automne, en hiver et au printemps en 2002–2003. Les longueurs de la tête et des tarses des mâles sont semblables dans les deux sites et celles des femelles légèrement plus grandes en Alaska qu’en Basse-Californie. Les bernaches semblent fonctionner sous des contraintes physiologiques semblables, mais les patrons d’allocation des nutriments diffèrent dans les deux sites. Les oiseaux qui hivernent en Alaska perdent au début de l’hiver des quantités de tissu adipeux de même ordre que celles qu’accumulent les oiseaux en Basse-Californie en fin d’hiver avant la migration. Les masses du corps, du tissu adipeux et des muscles du vol au milieu de l’hiver sont semblables dans les deux sites. La déposition saisonnière de tissu adipeux peut donc favoriser également le maintien sur place durant l’hiver ou la migration. La masse des gonades et celle du foie augmentent en fin d’hiver chez les oiseaux d’Alaska, mais non chez ceux de Basse-Californie, ce qui indique que les oiseaux qui hivernent en Basse-Californie peuvent retarder leur développement reproductif pour favoriser une allocation de leurs réserves aux besoins de la migration. La flexibilité phénotypique permet aux bernaches d’utiliser des sites d’hivernage extrêmement différents. Le site d’hivernage des bernaches dépend vraisemblablement plus des changements dans les conditions du milieu et de la disponibilité de la nourriture que des différences physiologiques entre les deux populations en hivernage.

Document Type: Research Article

Publication date: June 1, 2007

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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