Differential responses to weather and land-cover conditions explain spatial variation in winter abundance trends in a migratory bird of conservation concern

Effective conservation strategies for animal populations require knowledge
of relationships between population dynamics and their environmental
drivers. However, these processes often vary within animal populations,
requiring site-specific conservation planning. Given limited financial
resources, identifying groups of sites with similar population dynamics
can help practitioners efficiently implement conservation programs to
larger areas. We evaluated spatial patterns and environmental drivers of
wintering site trends in a migratory bird of conservation concern, the
Greenland white-fronted goose (Anser albifrons flavirostris). We used
latent class analysis to identify trend patterns in 35 years of abundance
data among 59 geographically discrete Greenland white-fronted goose
wintering sites. We developed a state-space abundance model in a Bayesian
framework to quantify the effects of weather and land-cover conditions
experienced throughout spring migration, summer breeding, autumn
migration, and wintering periods on variation in wintering site abundance.
We identified two main patterns in Greenland white-fronted goose abundance
trends: northeastern wintering sites declined on average by 2% per year,
while southwestern wintering sites declined on average by 14% per year.
Differential responses to weather and habitat conditions likely explained
variation among groups, as geese at southwestern wintering sites were more
negatively affected by harsh weather conditions (e.g., low temperatures
and high precipitation on breeding areas) and poor habitat conditions
(i.e., low-quality grasslands and croplands) on wintering areas. Future
conservation efforts to improve the suitability and nutritional quality of
agricultural areas, especially cereal croplands in autumn and early winter
and grasslands in late winter and early spring, could potentially improve
local habitat conditions, especially in the southwestern wintering sites
where abundance declines were steepest. Synthesis and applications: We
demonstrate the potential to delineate animal populations based on spatial
patterns in population dynamics using long-term abundance monitoring data,
which are commonly the only available data for conservation practitioners.
By grouping sites based on spatial patterns in local abundance trends, we
can further test hypotheses about how these groups are differentially
affected by changing environmental conditions. This information is
important for informing efficient conservation planning over large areas
when financial resources are limited.