TWEL Joni Downs Thesis

Population status and habitat utilization of greater sandhill cranes in Ohio
 
Joni A. Downs, MS
Advisor: Robert Gates
 
 
Ohio supports a small population (<15 breeding pairs) of greater sandhill cranes (Grus canadensis tabida) that is currently listed as endangered by the Ohio Division of Wildlife. The population has displayed little or no growth since it was established during the mid-1980s, and plans to restore the species by habitat restoration, habitat manipulation, and population augmentation are currently under consideration. The purpose of this study was to identify factors that currently limit growth of Ohio’s crane population in order to evaluate the potential for Ohio to support a viable breeding population of cranes and develop management recommendations for population enhancement.
 
The largest concentration of breeding pairs occurs at Killbuck Marsh Wildlife Area (KMWA) and Funk Bottoms Wildlife Area (FBWA) in Wayne and Holmes Counties, although breeding pairs are also present in Geauga and Trumbull Counties and near La Su An Wildlife Area (LSWA) in Williams County. Cranes nested in shallow marshes dominated by emergent vegetation that were located 29 ± 25 m (S.E.) from grass habitat and 246 ± 137 m from row crops. Breeding and sub-adult cranes spent >70% of daytime in shallow marsh and wet meadow and used these habitats primarily for nesting, resting, and comfort activities. Cranes fed in agricultural fields throughout the breeding season, utilizing crop stubble, plowed fields, and planted corn and soybean fields. Cranes used grass habitats extensively for food and cover during brood-rearing but rarely during other phases of the breeding cycle. Grass habitat that is near marshes used for nesting was identified as a critical habitat component to provide optimal breeding habitat for cranes.
 
Nesting success for cranes breeding at KMWA, FBWA, and LSWA averaged 30% during 2002-2004. Nest flooding was responsible for 70% of failed nesting attempts. Fledged colts averaged 12.5% of the fall population, an autumn age ratio that would support population growth. However, fledged colts comprised < 8% of the autumn population during 2002 and 2004, which is an age ratio that is below the lower limit required for a stable population. If productivity observed during 2002 and 2004 is more typical of long-term annual recruitment than the 3-year average, then Ohio’s crane population is limited by poor nesting success that is caused by flooding. Analysis of water level fluctuations at KMWA suggests that flood events of a magnitude that cause nest flooding occur 2-5 times annually during the breeding season, a frequency less than the incubation period of cranes, and the crane population at KMWA and FBWA appears to be limited by poor nesting success caused by flooding.
 
A Habitat Suitability Index (HSI) model was developed to identify suitable crane nesting habitat in northern Ohio using National Land Cover Data (NLCD) and a geographic information system. Nesting habitat suitability was evaluated on the basis of wetland vegetation type, wetland size, and the amount of grass habitat and row crops within 780 m of the wetland. The HSI model identified known crane nesting sites when herbaceous wetland was correctly classified in the NLCD habitat coverage. The HSI model identified that suitable, unoccupied habitat is available to cranes at Killdeer Plains and Big Island Wildlife Areas in Wyandot and Marion Counties, near La Due Reservoir in Geauga County, and in the Lake Erie marsh region.
 
HSI model output also was used to estimate carrying capacity for 5 habitat complexes in Ohio where suitable nesting habitat for cranes was identified. Carrying capacity was defined as the maximum number of suitable nesting sites that can be occupied simultaneously by breeding pairs, given that pairs are territorial and nests must be spaced 3,000 m apart. Carrying capacity was formulated as an Anti-Covering Location Problem (ACLP) and solved using optimization techniques. ACLP results indicate that Killbuck Marsh-Funk Bottoms, La Su An, and Aquilla-La Due habitat complexes are at or near carrying capacity defined by current crane habitat utilization patterns. Modeling results also indicate that the greatest potential for crane population expansion exists in the Lake Erie marsh region, while little opportunity exists at Killdeer Plains-Big Island, because availability of suitable nesting sites is limited.
 
Future status of cranes in Ohio will depend on long-term annual recruitment that is depressed by nest flooding, availability of suitable nesting habitat at sites where cranes currently breed, and expansion of the population into suitable habitats that are currently unoccupied. Management recommendations for population restoration include annual breeding pair surveys, continued population monitoring, wetland restoration, water level regulation, and habitat enhancement.