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Diet shifts of lesser scaup are consistent with the spring condition hypothesis

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We compared diets of lesser scaup (Aythya affinis (Eyton, 1838)) in the springs of 2000 and 2001 to those reported in the 1970s and the 1980s to determine whether forage quality has declined as predicted by the spring condition hypothesis. In Minnesota, we found that the current aggregate percentage of Amphipoda (an important food item) in lesser scaup diets was 94% lower than that reported from the same locations in the 1980s. Current mean individual prey mass of Amphipoda and Bivalvia in Minnesota were 86.6% and 85.1% lower than historical levels, respectively. In Manitoba, current aggregate percentages of Trichoptera and Chaoboridae in lesser scaup diets (1% and 0%, respectively) were lower than those reported from the same location in the 1970s (14% and 2%, respectively), whereas the percentage of Chironomidae (40%) was higher than that of historical levels (19%). Current mean individual prey mass of all insects, seeds,Chironomidae, and Zygoptera in Manitoba were 63.5%, 65.4%, 44.1%, and 44.9% lower than those of historical levels, respectively. The observed dietary shift from Amphipoda to less nutritious prey in Minnesota, coupled with lower mean individual prey mass in both locations, likely constitutes lower forage quality in lesser scaup diets, which is consistent with the spring condition hypothesis.

Nous comparons le régime alimentaire du petit fuligule (Aythya affinis (Eyton, 1838), désigné ci-dessous le fuligule) aux printemps de 2000 et de 2001 à ceux rapportés dans les années 1970 et 1980 pour déterminer si la qualité de l’alimentation s’est détériorée comme le prédit l’hypothèse des conditions printanières. Au Minnesota, le pourcentage combiné actuel d’Amphipoda (un aliment important) dans le régime des fuligules est de 94% inférieur aux valeurs signalées dans les mêmes sites dans les années 1980. Les masses moyennes individuelles courantes des proies, Amphipoda et Bivalvia, au Minnesota sont respectivement 86,6% et 85,1% inférieures à celles du passé. Au Manitoba, les pourcentages totaux actuels de Trichoptera et de Chaoboridae dans les régimes des fuligules (respectivement 1% et 0%) sont plus bas que ceux rapportés au même site dans les années 1970 (respectivement 14% et 2%); en revanche, le pourcentage deChironomidae (40%) est plus élevé que les valeurs du passé (19%). Les masses moyennes individuelles courantes des proies sont plus basses que par le passé au Manitoba, pour ce qui est des insectes totaux (de 63,5%), des graines (de 65,4%), des Chironomidae (44,1%) et des Zygoptera (44,9%). Le remplacement des Amphipoda dans l’alimentation par des proies moins nutritives, combiné à la masse moyenne individuelle réduite des proies, fournit vraisemblablement une qualité de nourriture moindre dans le régime des fuligules, ce qui est compatible avec l’hypothèse des conditions printanières.

Document Type: Research Article

Publication date: June 1, 2006

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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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