Monarch Butterfly (Danaus plexippus) Roost Site-Selection and Viability East of the Appalachian Mountains

The Monarch butterfly is a flagship species and pollinator whose populations have declined by approximately 85% in the last two decades. Their largest population overwinters in Mexico, then disperses across the eastern United States and Canada during April to August. Between September-December, the butterflies return south using two migratory flyways, one spanning the central United States and another following the Atlantic coast. They fly during the day and at night roost in large groups. Roosting habitat is essential to the continuation of the Monarchs’ migration, however, threats such as anthropogenic habitat disturbance and climate change potentially endanger sustainability of these habitats. The criteria that Monarchs use to select specific roost sites, and the landscape context where those sites are found, have received little study. I developed ecological niche models for the Atlantic Flyway roost sites using modeling algorithms, citizen scientist observations, and environmental variables that are known to affect Monarchs in the adult stage prior to migration. MaxEnt variable jackknifing identified proximity to surface water (Euclidean Distance to Coast, Lakes, and Rivers), elevation (Above Mean Sea Level), and vegetative cover (Land and Crop Cover Type) as the most important criteria. My model predicts 2.6 million ha of suitable roosting habitat in the Atlantic flyway, with greatest availability along the Atlantic coastal plain and Appalachian Mountain ridges. These models can be used to help prioritize survey and conservation efforts for Monarchs in areas most suitable for their roosting. I developed two novel methods for validating the models: a smartphone application to engage citizen scientists, and peer-informed comparisons with Google Earth imagery. I conducted a vulnerability assessment of predicted suitable roost habitat, assessed the connectivity of the habitat with Morphological Spatial Pattern Analysis, used Zonation software to create a relative value ranking of the Atlantic flyway region for Monarch roost site conservation, and mapped areas of high conservation value in the flyway in regards to their current predicted vulnerability. Predicted suitable roost habitats occurring in coastal areas (1 million ha) were more vulnerable than those further inland (1.6 million ha), where they parallel the Appalachian Mountains chain. The majority (73%) of roosting habitat occurs within non-fragmented core patches, and many of these patches are within the average daily flight distance (45 km) of migrating Monarchs. Although the flyway contains 18.5 million hectares of lands in conservation management, there was little overlap between the areas of high conservation value for migrating Monarch butterflies and current conservation lands, with only 7% of predicted suitable roost habitat currently in conservation holdings. These findings suggest that conservation of the Monarch migratory phenomenon may benefit most from land management action outside of current conservation lands to promote roost habitat.

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