Habitat use by Red-breasted Merganser (Mergus serrator) broods at Kouchibouguac National Park, New Brunswick


             Recruitment of juvenile waterfowl requires that adequate brood-rearing habitat be available.  Despite breeding in a variety of fresh and salt water wetlands, little is known about the brood habitat requirements of Nearctic Red-breasted Mergansers (Mergus serrator) that breed in marine environments, particularly at coastal barrier island sites.  The objective of the study was to determine habitat selection by Red-breasted Merganser broods at two scales (home range and sites within home range). We used a landscape-level approach to habitat selection where discrete coastal habitats were delineated from the Canadian Wildlife Service’s Maritime Wetlands Inventory.  Over three years (2002-2004), habitat use was determined daily for 11 radio-marked merganser broods originating from a breeding colony located on three barrier islands at Kouchibouguac National Park, New Brunswick.  At both scales of study, radio-marked broods preferred continental and barrier island estuarine intertidal flats.  Adjacent tidal wetlands of estuarine intertidal flat habitat provided young broods (< 10 days post-hatch) with concealed resting and loafing sites amidst emergent salt water cordgrass (Spartina alterniflora). Older broods typically did not seek emergent vegetation and were often observed loafing along the sandy shores of the intertidal flats located along the barrier island complex. Preliminary fish sampling evidence suggested that the intertidal regions of the estuarine system support a large number of small fish species (e.g. Atlantic Silversides Menidia menidia) in high abundance throughout the late summer brood-rearing period.  Tidal river habitat was avoided for brood-rearing despite its proximity to the nesting islands and apparent large prey base.  Interspecific competition with Common Merganser (Mergus merganser) broods at tidal river sites may be a proximate factor in the evolution of habitat selection of mergansers at Kouchibouguac National Park. Priorities for future studies include the influence of habitat on Red-breasted Merganser duckling survival probabilities and investigations concerning the evolution of post-hatch brood amalgamation (crèche formation).

 Shawn Craik

 

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