Estimating carrying capacity for sandhill cranes using habitat suitability and spatial optimization models

Northern Ohio supports a small population of greater sandhill cranes (Grus canadensis tabida) that is currently listed as state-endangered. Population restoration efforts are currently under consideration, although it is not known if habitats in the state can support additional nesting pairs. Accurate estimates of breeding pair carrying capacity are necessary before conservation efforts can be effectively developed and implemented. We estimated carrying capacity for nesting sandhill cranes using habitat suitability and spatial optimization models. We first developed a spatially explicit habitat suitability index (HSI) model to identify suitable nesting sites at five locations in northern Ohio. We then used the HSI output to estimate the carrying capacity at each location. We modeled carrying capacity as an anti-covering location problem, a spatial optimization model that determines the maximum number of breeding pairs an area can support, given that nests must be spaced 3000 m apart. Our results indicate that habitats in Ohio where cranes currently breed are near carrying capacity, while unoccupied suitable habitats are available in other portions of the state. This analysis enables wildlife managers to identify priority locations for crane conservation in Ohio and to determine which restoration efforts (e.g. habitat restoration or population augmentation) are most likely to succeed at each location. Our methodology provides an important and innovative conservation tool that can be applied to other species with strong attachment to sites (e.g. nest or den) that are optimally spaced at some minimum distance from conspecifics, competitors, predators, or sources of disturbance.