Monarch butterfly (Danaus plexippus) breeding distribution and habitat preferences in Southeastern Ontario

Habitat loss is considered a strong driver of the decline of the eastern migratory population of the North American monarch butterfly (Danaus plexippus). While research has focused on the loss of suitable habitats in agricultural areas in the American Midwest, little is known about monarch breeding habitat preferences at the northern limits of its summer range in Canada. I first conducted a literature review on monarch habitat preferences and population dynamics across its North American range and on the role of community science in the monitoring of spatial dynamics. Seventeen years of community science records (n=5461) reporting the presence of butterfly species in southeastern Ontario were then used to compare land covers and spatial attributes of butterfly records that included the monarch with records that did not. The models indicate that the probability of observing monarchs, compared to other butterflies in this region, decreases going northward and westward, away from water bodies, and with increasing deciduous or needleleaf forest cover. Clusters of monarch observations (hot spots) are found north of Lake Ontario. Compared with cold spots where the probability of observing the monarch is low, the hot spots tend to have more shrubland and less deciduous forest and urban land cover. A field comparison of the vegetation at a subset of hot and cold sites identifies potential nectaring species at these latitudes, and compares how milkweed abundance, plant richness, and the diversity of potential nectaring plants drive habitat preferences. It offers some of the first evidence that, in this region, milkweed abundance may not be a limiting factor for monarch breeding habitat selection. It also shows a greater ecological gradient in potential nectaring species assemblages in hot spots than in cold ones, ranging from grassland species in conserved lands in the developed regions near Lake Ontario, to forest edge species and shrubs within rights of way in forested regions to the north. While the importance of preserving monarch resources in agricultural landscapes has been acknowledged, the role of successional habitats in forested landscapes has been little considered. This research shows that preserving such spaces is an important feature of monarch conservation at the northern range edge. This study also demonstrates the value of community science data to delineate areas of conservation interest

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