Factors influencing emigration of Ross's and snow geese from an Arctic breeding area

Abstract

Emigration is one of the most difficult demographic rates to estimate, yet understanding movement among populations has important consequences for wildlife conservation. We studied factors that affected emigration by adult Ross's geese (Chen rossii) and lesser snow geese (C. caerulescens caerulescens) during a demographic study from 1997 to 2013 of nesting geese at the Karrak Lake colony south of Queen Maud Gulf in the Central Canadian Arctic. Rising abundance of both species in recent decades has led to concerns about their impacts on Arctic ecosystems. We used Burnham's model to estimate true survival and fidelity (i.e., the complement of emigration). Mean estimates of fidelity were higher for Ross's geeseFidelity declined with prior nesting season abundance in both species with evidence that a reduction in population size led to greater fidelity in the following year. Fidelity was positively influenced by mean nest success in the previous year with similar responses by both species. However, years of low nest success were more frequent for snow geese resulting in higher emigration. We expected that deeper snow before nesting would motivate greater emigration but found the opposite effect in both species, suggesting that individuals may be discouraged from dispersing in snow-covered landscapes. We also tested whether a large decline in the number of snow geese nesting at Karrak Lake in 2007-2008 was related to a mass emigration event but found no evidence for a change in fidelity in these years. Moreover, survival of both species showed an increasing trend from 1997 to 2013 so the decline in nesting snow geese likely was an outcome of temporary non-breeding, rather than emigration or death. The destination of emigrants remains unknown, but we expect this movement has broader consequences for metapopulation dynamics of light geese across the central

Annual survival and seasonal hunting mortality of midcontinent snow geese

“…Our derivations of seasonal kill rate for lesser snow geese in the midcontinent uncovered spatiotemporal variation among years, and contrasting seasonal patterns between age groups and breeding locations. Our findings are consistent with recent evidence supporting high population size and reduced harvest impact among geese in northern and southern breeding areas (Alisauskas et al , Koons et al , Wilson et al ). In general, however, our estimates suggest that declining kill rates accounted for very little of the annual mortality, which itself has declined over time.…”

Decadal declines in avian herbivore reproduction: density‐dependent nutrition and phenological mismatch in the Arctic

“…Our estimate of colony population size pertained to the number of geese breeding at Karrak Lake but did not include non-breeders near the colony; however, both breeding and non-breeding geese destined for Karrak Lake and surrounding areas likely stop at the same northern staging areas above the tree line in the Arctic plains. Nevertheless, a sharp increase in population size for the region is evident , Kerbes et al 2014, Wilson et al 2016) and the long-term decline in productivity was consistent with density-dependence detected in other regions (Cooch et al 1989, Williams et al 1993, Aubry et al 2013.…”

“…, Wilson et al. ). Reduced recruitment and increased survival are predicted to alter the population age distribution toward older individuals with associated senescent reductions in reproduction and subsequent momentum effects on population trajectories.…”

“…Consequently, we used a time series of 23 breeding seasons (1992–2014) to estimate the median date of NDVI 50 (our index of forage availability) on the brood‐rearing area (~5 × 10 6 km 2 ) north of Karrak Lake (Slattery and Alisauskas , Wilson et al. ). Daily global NDVI grids (0.05° resolution) were obtained from two sources: the Long Term Data Record Version 3 collected by the Advanced Very High Resolution Radiometer (AVHRR) for 1982–1999 and from the Earth Science Data Record of preprocessed NDVI collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) for 2000–2010 (data available online ) , .…”

Density‐dependent and phenological mismatch effects on growth and survival in lesser snow and Ross's goslings

“…Nesting ecology of Ross's and snow geese has been studied at Karrak Lake since 1991. Nest searching was conducted within 30 metre radius circular plots mapped across the colony using a systematic 1-km grid based on the Universal Transverse Mercator (UTM) system , Wilson et al 2016. At each plot, eggs in nests were uniquely marked, counted and measured.…”