Predation rates, timing, and predator composition for scoters (Melanitta spp.) in marine habitats. Canadian Journal of Zoology 90

• Main Authors: Eric M Anderson, Daniel Esler, W Sean Boyd, Joseph R Evenson, David R Nysewander, David H Ward, Rian D Dickson, Brian D Uher-Koch, Corey S Vanstratt, Jerry W Hupp
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2012
• Subjects: Brune; Pacific; macreuse brune; Melanitta fusca; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1080.3551; http://www.sfu.ca/biology/wildberg/papers/Anderson%20et%20al.%202012%20CJZ.pdf

Abstract: Studies of declining populations of sea ducks have focused mainly on bottom-up processes with little emphasis on the role of predation. We identified 11 potential predators of White-winged Scoters (Melanitta fusca (L., 1758)) and Surf Scoters (Melanitta perspicillata (L., 1758)) in North American marine habitats. However, of 596 Scoters marked with VHF transmitters along the Pacific coast, mortalities were recovered in association with just two identifiable categories of predators: in southeast Alaska recoveries occurred mainly near mustelid feeding areas, while those in southern British Columbia and Washington occurred mainly near feeding areas of Bald Eagles (Haliaeetus leucocephalus (L., 1766)). Determining whether marked Scoters had been depredated versus scavenged was often not possible, but mortalities occurred more frequently during winter than during wing molt (13.1% versus 0.7% of both species combined, excluding Scoters that died within a postrelease adjustment period). In two sites heavily used by Scoters, diurnal observations revealed no predation attempts and low rates of predator disturbances that altered Scoter behavior (≤0.22/h). These and other results suggest that predation by Bald Eagles occurs mainly at sites and times where densities of Scoters are low, while most predation by mustelids probably occurs when Scoters are energetically compromised. Résumé : Les études des populations en déclin de canards marins se sont intéressées surtout aux processus ascendants avec peu d'emphase sur le rôle de la prédation. Nous avons identifié 11 prédateurs potentiels de la macreuse brune (Melanitta fusca (L., 1758)) et de la macreuse à front blanc (Melanitta perspicillata (L., 1758)) dans des habitats marins nordaméricains. Cependant, chez 596 macreuses porteuses d'émetteur VHF le long de la côte du Pacifique, nous avons noté des mortalités associées à seulement deux catégories identifiables de prédateurs : dans le sud-est de l'Alaska, les émetteurs ont été récupérés principalement près des aires ...