Population biology of Ross's geese at McConnell River, Nunavut

Abstract

Understanding what influences movement patterns in animals is important to the understanding of colonization, range expansion, and source–sink dynamics. Ross’s geese (Chen rossii) have been expanding their nesting range eastward, and, as recently as 1994, have been nesting in large numbers in such newly colonized areas. I sampled nests at the McConnell River Migratory Bird Sanctuary (MCR), the largest known Ross’s goose nesting colony outside the Queen Maud Gulf Migratory Bird Sanctuary (QMG) to estimate its nesting population size. To understand whether immigration by Ross’s geese to a new colony located outside traditional nesting areas has an adaptive basis, I compared nutritional, nesting, and survival metrics between geese nesting at the MCR and those nesting at Karrak Lake (KAR) in QMG. I hypothesized that because of longer nesting season, Ross’s geese at MCR would have more fat and protein reserves, larger clutch sizes, and greater nest success than those at KAR. Additionally, I hypothesized that population change at MCR was due largely to in situ recruitment. To better understand factors motivating dispersal, movement by Ross’s geese between nesting attempts at MCR was measured between years. I hypothesized that dispersal distance of nesting females between years t, and t+1 was a function of both a female’s own reproductive success as well as that of her neighbours.

In 1997 over 23,000 Ross’s geese were counted at MCR. By 2007, population estimates (± SE) had increased to 81,408 (±12,367). Survival of both juvenile and adult geese marked at MCR was similar to those nesting at KAR; however, recovery rate estimates were greater than those for KAR. On average, Ross’s geese arrived and initiated nests at MCR seven days earlier than at KAR. Abdominal fat was lower when nest initiation date was later in both areas, but was generally greater in geese nesting at MCR. Similarly, there was more indexed protein in geese at MCR than those at KAR in 2 of 3 years. Nesting indices such as clutch size and nest success did not show a consistent area effect, which interacted with a year effect.

Ross’s geese at MCR did not appear to use individual or conspecific reproductive success when deciding if or how far to disperse between years, and temporary emigration rates also did not vary based on reproductive success the previous year. Instead, variables other than prior individual or neighbour nest success influenced Ross’s goose nest site selection and colony fidelity. The number of Ross’s geese nesting at MCR increased at an average rate of 11.4% per year from 2003–2007, despite no increase (0%) from 2006 to 2007. Vital rate information gathered during this time suggests that immigration may have contributed to this growth; however, with few assumptions it can be concluded that MCR is a sustainable population. As a result, studies of geese breeding at MCR provide evidence that arctic geese are capable of successfully colonizing nesting areas great distances beyond historic range.