Cumulative mortality and population parameters for a vulnerable seabird, the Razorbill Alca Torda, in Atlantic Canada

Lavers, Jennifer L. (2007) Cumulative mortality and population parameters for a vulnerable seabird, the Razorbill Alca Torda, in Atlantic Canada. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This thesis was developed within the framework of a conservation project to examine the demographics of a long-lived seabird, the Razorbill Alca torda, across its North American breeding range. Research was designed to (a) take advantage of two relatively long-term Razorbill capture-mark-recapture and productivity data sets available for two representative breeding islands in different oceanic regimes and (b) fill in research gaps to predict Razorbill population trends under various scenarios. I quantified the impacts of intraspecific kleptoparasitism, dispersal, fox predation, and hunting bycatch on the population parameters of the Razorbill at the Gannet Islands, Labrador and Machias Seal Island, New Brunswick. The level of intraspecific kleptoparasitism on the Gannet Islands is the highest reported for any seabird species (attack rate = 0.69, success rate = 0.18-0.22) and is implicated in the low productivity rates observed. Productivity at the Gannet Islands during 2004-2006 was the lowest reported since monitoring began in the 1980s, with only 39% of pairs successfully producing a chick. Long-distance breeding dispersal was more frequent than previously thought; distances moved by 40 birds ranged from 60 km to more 3,210 km. My estimates of adult and pre-breeder survival during 1995-2006 (Gannet Islands: 0.890 and 0.482 respectively; Machias Seal Island: 0.967 and 0.778 respectively) contrasted sharply with other studies. Specifically, adult survival at the Gannet Islands was the lowest ever reported for the species, and at Machias Seal Island it was the highest ever reported. The projected growth rate (λ) for the Gannet Islands Razorbill population predicted by models was 0.9475 for the Gannet Islands and 1.0613 for Machias Seal Island. Modeling also suggested that hunting mortality reduced the Gannet Islands projected population growth rate by 0.0603, while fox predation reduced population growth by 0.0126. Together these sources reduced the projected population growth rate by 0.0729. Although the Razorbill population on Machias Seal Island appears to be growing, without substantial immigration the Gannet Islands population is expected to decline. The Gannet Islands Razorbill population is the largest in North America and therefore represents a significant conservation concern. Recommendations for the continued monitoring of both populations and development of specific management plans to control foxes on the Gannet Islands and investigate hunting bycatch are discussed.

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