Contrasting Population Trends at Two Razorbill Colonies in Atlantic Canada: Additive Effects of Fox Predation and Hunting Mortality?
Lavers, JL and Jones, IL and Robertson, GJ and Diamond, AW, Contrasting Population Trends at Two Razorbill Colonies in Atlantic Canada: Additive Effects of Fox Predation and Hunting Mortality?, Avian Conservation and Ecology, 4, (2) pp. 3 http://www.ace-eco.org/vo14/iss2/art3/. ISSN 1712-6568 (2009) [Refereed Article]
We developed a stochastic, stage-based, matrix-projection population model to assess
population viability and estimate the impact of mortality caused by hunting, illegal and incidental to the
murre (Uria sp.) hunt, and fox (Alopex lagopus) predation on Razorbill (Alca torda) populations breeding
on the Gannet Islands, Labrador, the "affected" population, and Machias Seal Island, New Brunswick, the
"unaffected" population. We estimated the potential population growth rate in the absence of anthropogenic
mortality sources by using juvenile survival estimates from the relatively unaffected Machias Seal Island
Razorbill population. We used data collected on fox predation on the Gannet Islands from 19782009 to
estimate the change in productivity as a result of fox presence. The intrinsic growth rate (l) of the stochastic
matrix based on vital rates from the Gannet Islands was 0.957±0.008 and 1.058±0.005 for Machias Seal
Island. Hunting mortality reduced the predicted Gannet Islands population growth rate by 0.033, while fox
predation reduced population growth rate by 0.017. These sources combined reduced the baseline population
growth rate by 0.050. According to our model, the Razorbill population on Machias Seal Island appears
to be growing rapidly. In contrast, the Gannet Islands population may decline, likely because of hunting.
However, oceanographic differences between the two areas and uncertainty regarding dispersal behavior
in this species may also contribute to the disparity between populations. Based on our findings, we make
several recommendations for the conservation and management of Razorbills in Atlantic Canada.
Hunting mortality, fox predation, seabird population dynamics