Conclusion of No Decline in Summer Monarch Population Not Supported

  title={Conclusion of No Decline in Summer Monarch Population Not Supported},
  author={John M. Pleasants and Ernest H. Jr. Williams and Lincoln Pierson Brower and Karen S. Oberhauser and Orley R. Taylor},
  journal={Annals of The Entomological Society of America},
Seven research papers and a cover article recently appeared in the Annals of the Entomological Society of America (online, 5 August 2015) that examined several long-term monarch butterfly monitoring programs. In their cover summary, Davis and Dyer (2015) focused on three studies that concluded there had been no decline over the past two decades in summer breeding numbers for the eastern North American population. This purported lack of decline is at odds with both the observed decline in the… 

No broad decline of breeding monarch butterflies in North America: implications for conservation efforts

A series of long-term monarch monitoring datasets reveal a robust resiliency in summer populations that thus far has allowed recovery from losses during the winter, and monarchs may not require as much breeding habitat restoration as once thought.

A Review of Published and Unpublished Findings from 20 Long-term Monitoring Studies of Eastern Monarch Butterflies: the Population was Never in Danger, Despite Recent Winter Colony Declines

There are a large number of wildlife and insect species that are in trouble on this planet, and most believe that monarch butterflies in eastern North America are too, because of the well-publicized

Monarchs in decline: a collateral landscape‐level effect of modern agriculture

Modeling studies that simulate lifetime realized fecundity at a landscape scale, direct counts of milkweeds, and extensive citizen science data across the breeding range suggest that a herbicide‐induced, landscape‐level reduction in milkweed has precipitated the decline in monarchs.

Linking the continental migratory cycle of the monarch butterfly to understand its population decline

Threats to several of the world's great animal migrations necessitate a research agenda focused on identifying drivers of their population dynamics. The monarch butterfly is an iconic species whose

Evaluating the Migration Mortality Hypothesis Using Monarch Tagging Data

There is no disconnection between late summer and winter population sizes, and migration success did not decrease during this period, so the main determinant of yearly variation in overwintering population size is summer population size with migration success being a minor determinant.

Butterfly abundance declines over 20 years of systematic monitoring in Ohio, USA

These results from the most extensive, systematic insect monitoring program in North America demonstrate an ongoing defaunation in butterflies that on an annual scale might be imperceptible, but cumulatively has reduced butterfly numbers by a third over 20 years.

Density-dependence in the declining population of the monarch butterfly

The Eastern monarch butterfly population has significantly declined over the last two decades creating growing concerns around its conservation status, and it is shown that the overwintering population exhibited a negative density-dependence and that, after accounting for the density effect, the population growth rate tended to decline over time.

Long-Term Trends in Midwestern Milkweed Abundances and Their Relevance to Monarch Butterfly Declines

A long-term plant survey from Illinois is used to evaluate whether trends in milkweed abundance have caused monarch decline and to highlight the habitat-management practices that promote milkweeds.

A trans-national monarch butterfly population model and implications for regional conservation priorities

1. The monarch has undergone considerable population declines over the past decade, and the governments of Mexico, Canada, and the United States have agreed to work together to conserve the species.

Multiscale seasonal factors drive the size of winter monarch colonies

A multiscale modeling approach reveals that continental-scale landscape greenness during migration and the amount of forest cover at winter sites significantly influence arrival colony sizes, and demonstrates a demographic link between summer and fine-scale winter population sizes.



Long-Term Trends in Eastern North American Monarch Butterflies: A Collection of Studies Focusing on Spring, Summer, and Fall Dynamics

The collection of articles in this special feature was produced by researchers associated with a variety of nation-wide citizen science projects that have been tracking monarchs for many years, with the overarching goal of identifying long-term trends in their abundance or distribution outside of the wintering period.

Investigating Long-Term Changes in the Spring Migration of Monarch Butterflies (Lepidoptera: Nymphalidae) Using 18 Years of Data From Journey North, a Citizen Science Program

It is found monarchs are being sighted later at a rate of 1 d later every 4 yr, which could be interpreted as a sign of reductions in monarch abundance, and a potential decline in the geographic range of the initial spring migration wave.

Population Trends of Monarchs at a Northern Monitoring Site: Analyses of 19 Years of Fall Migration Counts at Peninsula Point, MI

It is argued that preserving migratory habitats and resources, as well as reducing anthropogenic activities that hinder migration, should be the highest priorities for conserving monarchs in eastern North America.

Immature Monarch Survival: Effects of Site Characteristics, Density, and Time

It is estimated that across all years in the north-central United States, where the most data is used, a minimum number of ∼29 milkweed plants are required to produce an adult monarch that will be part of the fall migratory generation.

Are migratory monarchs really declining in eastern North America? Examining evidence from two fall census programs

Abstract.  1. The status of the eastern North American monarch butterfly population is a highly sensitive issue, given that winter and breeding habitats are being lost at an alarming rate each year,

The Disconnect Between Summer and Winter Monarch Trends for the Eastern Migratory Population: Possible Links to Differing Drivers

An alarming steepening in the decline of winter colony size since 2008 is discovered, and there is still an association between the yearly fluctuations between these key periods, suggesting a link in population dynamics throughout the year.

Temporal and spatial overlap between monarch larvae and corn pollen

It is found that monarchs use milkweed in cornfields throughout their breeding season, and that per plant densities are as high or higher in agricultural habitats as in nonagricultural habitats, suggesting that agricultural practices such as weed control and foliar insecticide use could have large impacts on monarch populations.

Decline of monarch butterflies overwintering in Mexico: is the migratory phenomenon at risk?

Abstract.  1. During the 2009–2010 overwintering season and following a 15‐year downward trend, the total area in Mexico occupied by the eastern North American population of overwintering monarch

Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population

There has been a large decline in milkweed in agricultural fields in the Midwest over the last decade, coincident with the increased use of glyphosate herbicide in conjunction with increased planting of genetically modified (GM) glyphosate‐tolerant corn (maize) and soybeans (soya).

Response to Davis: choosing relevant evidence to assess monarch population trends

Abstract.  1. We recently reported in this journal that the abundance of the migratory population of monarch butterflies is declining ( Brower et al., 2011 ). Davis ( Davis, 2011 ) subsequently