Designing optimal conservation strategies for monarch butterflies in agricultural landscapes

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Monarch butterflies (Danaus plexippus) in eastern North America have declined by 95% in the last 20 years due to loss of milkweed plants, the food plant for caterpillars, in agricultural landscapes. Agricultural companies are keenly aware of the importance of conserving biodiversity and are actively seeking the best approach towards the restoration of milkweed within agricultural landscapes. However, simply planting milkweed in as many locations as possible is likely not the most biologically-effective solution because female butterflies may prefer certain types of milkweed patches. We propose to use milkweed, nectar plant and monarch surveys and a state-of-the-art radio-telemetry array network to examine habitat selection of monarch butterflies in southern Ontario. Our objectives are (1) determine the characteristics of milkweed patches female butterflies select to lay eggs, (2) determine the density of milkweed patches that optimize monarch larvae survival, and (3) validate habitat selection models by tracking radio-tagged monarchs. To achieve objectives 1 and 2, we will count monarch eggs and larvae each week on at least 500 plants in row-crop agriculture, natural vegetation, and road right-of-ways. To determine the characteristics of habitat selected by females for laying eggs we will test if egg presence/absence is related to land cover (agriculture, natural vegetation, right-of-way), milkweed density, patch size, and plant characteristics (age, height, flowing status, health status). For objective 2, we will calculate larvae survival as the proportion of 5th instars to eggs and then test if larvae survival is related to land cover, milkweed density and milkweed patch size. The product of the egg laying and larvae survival relationships gives a predicted habitat quality index for any location in the landscape. To achieve objective 3, we will compare the predicted habitat quality map to habitat selected by female monarch butterflies fitted with radio-tags and following their movement using an automated radio-telemetry array (http://motus-wts.org/). Our results will identify the ideal density and spatial arrangement of milkweed plants in restoration efforts to provide maximum benefit to monarch butterfly population recovery.