The decline of the eastern population of the migratory monarch has become a topic of great concern, but has been based entirely on patterns observed in overwinter colony sizes. Less attention has been paid to population trends during other phases of the migratory cycle. Here, we present an analysis of trends using three monitoring programs, one focused on overwinter colony size and two focused on summer breeding grounds. We discovered an alarming steepening in the decline of winter colony size since 2008. However, population indices from two independent summer monitoring programs were characterized by high year-to-year variability and no statistically detectable trends over time. Despite the mismatch in summer and winter patterns, there is still an association between the yearly fluctuations between these key periods, suggesting a link in population dynamics throughout the year. Further, a suggestion of a downturn near the end of the summer time-series should be carefully tracked into the future. We discuss two possible reasons for this disconnect: 1) higher levels of variance or possibly biased sampling could weaken any statistical signal, and 2) losses during fall migration could potentially contribute to overwinter declines.
How to translate text using browser tools
1 September 2015
The Disconnect Between Summer and Winter Monarch Trends for the Eastern Migratory Population: Possible Links to Differing Drivers
Leslie Ries,
Douglas J. Taron,
Eduardo Rendón-Salinas
ACCESS THE FULL ARTICLE
It is not available for individual sale.
This article is only available to subscribers.
It is not available for individual sale.
It is not available for individual sale.
conservation
ecology and population dynamics
papilionidae