![butterfly clusters butterfly clusters](https://i.pinimg.com/736x/9c/13/2a/9c132afd0a4e04b4245c3c03ca3af3b0--butterfly-migration-monarch-butterfly.jpg)
Finally, we discuss the prospect of completely losing migratory monarchs from western North America and what this entails for monarch conservation. We also discuss the concept of adaptive capacity in eastern and western monarchs as well as non‐migratory populations outside of the monarch's primary North American range. We suggest future studies that could improve our understanding of differences between eastern and western monarchs.
![butterfly clusters butterfly clusters](https://images.fineartamerica.com/images/artworkimages/mediumlarge/1/cluster-of-monarch-butterflies-sheila-fitzgerald.jpg)
Eastern and western monarchs occupy distinct environments and show some evidence for phenotypic differentiation, particularly for migration‐associated traits, though population genetic and genomic studies suggest that they are indistinguishable from one another. In this review, we focus on phenotypic and genetic differentiation between eastern and western monarchs, with the goal of informing researchers and policy‐makers who are interested in monarch conservation. However, the degree to which western monarchs are a distinct biological entity is uncertain. Declines in western overwintering monarchs-more than 99.9% since monitoring began-are especially acute.
![butterfly clusters butterfly clusters](https://hcastro.org/wp-content/uploads/2016/09/Butterfly-Cluster.jpg)
![butterfly clusters butterfly clusters](https://c8.alamy.com/comp/D1GFKJ/clusters-of-monarch-butterflies-D1GFKJ.jpg)
Monarch butterflies are a species of conservation priority due to declining overwintering populations in both eastern and western North America. We conclude that it will be necessary to consider spatial effects when studying or managing western monarch butterfly overwintering habitats, and that interpretations of habitat selection to date likely commingle habitat selection on the local and geographical scales. Rather, we find that microclimatic attributes in aggregation locations vary spatially with latitude, and that aggregation conditions exist in a large portion of each grove. We find no evidence supporting the hypothesis that aggregation locations have a unique microclimate that differs significantly from that of other locations inside the grove or that aggregation locations are uniform in their microclimatic attributes across overwintering groves. We tested the hypothesis that monarchs aggregate in locations in groves that have a unique microclimate that is consistently selected across groves (the microclimate hypothesis). We studied nine groves on the coast of California, and at each we collected temperature, humidity, and light data from grove edges, grove interiors, and aggregation locations for several weeks during the overwintering season. Therefore, we explore monarch overwintering habitat selection to determine whether an explicit spatial framework is necessary. However, western monarch butterflies are migratory thus, previous habitat selection studies could have commingled selection at different scales into a single local scale in the site of aggregation. Specifically, that microclimate habitat selection occurs when monarchs form dense overwintering aggregations in overwintering groves. To date, overwintering habitat selection by western monarch butterflies has primarily been studied assuming the microclimate hypothesis. Western monarch butterflies migrate seasonally to overwintering groves at geographically predictable locations along the coast of California. Migratory species are expected to demonstrate habitat selection that occurs at multiple spatial and temporal scales. The microclimatic advantages of the monarchs' clustering behavior on fir boughs add to the known repertoire of the butterflies' overwintering adaptations to the high altitude environment that they occupy each year from November through March. The differences were small, but these studies were conducted during calm, moderate conditions, and the effects are likely to be more pronounced under more severe weather, including mid-winter storms and late season aridity. Consequently, the butterflies inside the clusters may have gained some protection from freezing, reduced their rate of lipid burning, and lowered their rate of desiccation. The inside of the clusters remained significantly warmer at night and significantly cooler during the day, with higher relative humidity during both day and night. We inserted hygrochrons (miniaturized digital hygrothermographs) into clusters for two-day periods during the 2006––08 winters and compared temperature and relative humidity inside and outside the clusters. We tested the hypothesis that the clustering behavior of the butterflies further moderates the microclimate they experience. Monarch butterflies form dense clusters in their overwintering colonies in the mountains of central Mexico, where forest cover provides protection from environmental extremes.