Influence of habitat quality and resource density on breeding-season female monarch Butterfly Danaus plexippus movement and space use in north-central USA agroecosystem landscapes.
The eastern North American monarch butterfly is at risk of quasi-extinction due, in part, to the loss of breeding habitat in agricultural landscapes of the USA Midwest. Because adult females are not patch residents, egg abundance and distribution across the landscape are a function of their perceptual range, flight directionality and flight step lengths. Conservation actions that account for habitat use in agricultural landscapes can enhance functional connectivity. Field-captured females (n = 114) were released in a 64-ha area containing restored prairies, grass-dominated fields and crop fields in Floyd County, Iowa, USA, and two 1,000 m linear north-south sections of grass-dominated roadside along secondary roads (~35 ha) with different proximity to prairie habitat in rural Story County, Iowa. Radio-tagged or untagged monarchs were released in areas with high density, low density and zero density of forage and oviposition resources, as well as on habitat edges between high- and zero-density habitats. Monarchs were observed for 1 hr. Radio-tagged individuals that flew beyond visual detection were relocated using handheld radiotelemetry. Monarchs moved within and between habitat classes and typically performed upwind search behaviour. Monarchs successfully located resources, with some flying over 500 m to find high-density areas, providing evidence that the monarch's perceptual distance is >100 m. Regardless of habitat class or field site, most step lengths were <50 m, and turn angles were directional. Large steps (≥50 m) crossing habitat boundaries occurred with approximately half of the monarchs, which may indicate initiation of long-range searches for suitable habitat, consistent with their vagile behaviour. Establishing habitat patches 50 m apart in agricultural landscapes would facilitate efficient movement. Synthesis and applications. This study provides an extensive dataset of directly observed breeding-season monarch butterflies to assess the utilization of agricultural landscapes. Documentation of step lengths >50 m in complex, agricultural landscapes would not have been possible without the aid of radiotelemetry. Results provide improved estimates of perceptual range and flight patterns within and between habitat patches that support models that simulate natural population dynamics to enable conservation planning at a landscape scale.