Levels of Fecal Corticosterone in Released Sandhill Cranes: An Indicator of Potential Stress for Reintroduced Whooping Cranes
The use of fecal corticosterone assays in North American cranes has been limited to controlled laboratory trials performed with sandhill cranes (Grus canadensis),3,4 a common surrogate species used in crane research targeted to benefit endangered whooping cranes (Grus americana). These studies have confirmed that fecal corticosterone reflects changes in serum corticosterone brought about by adrenocortical stimulation following administration of ACTH. We chose to apply this assay to a specific release project where the ability to repeatedly handle birds for health evaluations was limited and supplementary diagnostic information was needed to fully assess stress induced by the methods used to rear the cranes prior to release. The objective of our pilot study was to document and compare ∼3-month trends of fecal corticosterone (FC) concentrations in two cohorts of sandhill cranes raised for release to the wild.
During summer and early fall 2000, sandhill cranes (Group 1, n=14) reared in isolation from humans were transferred from Maryland to Wisconsin and trained to fly after ultralight aircraft as a prelude to an aircraft-guided 1250 mile migration to Florida (http://bringbackthecranes.fws.gov/) (VIN editor: Link not accessible 2/26/21).2 A smaller group of sandhill cranes (Group 2, n=8) were reared using similar techniques in Wisconsin but did not experience directed ultralight aircraft training; these birds were released using a single bird release method.1 Fresh feces were collected from Group 1 (n=47) individuals at arrival in Wisconsin in late June, and then anonymously from their pens approximately every 2 weeks until migration in the first week of October. Feces were available slightly earlier from Group 2 (n=49), and with individual identification until the last samples acquired in late September. Feces were frozen within 2 hours at -20°C and thawed later for analysis. All samples were subject to radioimmunoassay for determination of corticosterone levels (ng/g) using established protocols.4 Levels >200 ng/g were considered increased over baseline.4
Increased FC levels (median 292.4 ng/g, range 59.9–650.7 ng/g, n=12) were observed in several Group 1 individuals upon arrival in Wisconsin, likely reflecting the stress of shipment. The lower FC levels observed in some cranes may have been due to sampling of feces produced prior to a hormonal increase. Corticosterone elevation in feces may not occur for 2 hours after adrenocortical stimulation.4 FC levels in Group 1 birds returned to baseline levels that were sustained throughout the remainder of the study (median 93.1 ng/g, range 61.2–263.6 ng/g, n=32), despite increasing contact time with the ultralight aircraft and a shifting dominance hierarchy within the group. FC levels in Group 2 remained consistent throughout the study period (median 111.3 ng/g, range 22.8–401.0 ng/g, n=49). There were occasional individual perturbations; including two cases that could be attributed to handling for banding and radiotagging 3 hours prior to fecal collection. There were no statistically significant differences in FC levels between the two groups when samples obtained close in time were compared. Significant disturbances, such as shipping, restraint for health examinations, and banding and radiotagging procedures appear most linked to increases in FC in sandhill cranes rather than stress invoked by the rearing and release methods used.
We intend to extend this initial study and apply FC monitoring to whooping crane reintroduction efforts. Knowledge of how the unique manipulations used for reintroduction of this endangered migratory species may subtly affect health is paramount to understanding the dynamics of the birds’ behavior and survival during migration and after release.
1. Ellis, D. H., D. P. Mummert, M. Kinloch, C. Mellon, T. Dolbeare, and D. Ossi. In press. The one-by-one method for releasing cranes. Proc. North Am. Crane Workshop 8.
2. Lishman, W. A., T. L. Teets, J. W. Duff, W. J. L. Sladen, G. G. Shire, K. M. Goolsby, W. A. Bezner Kerr, and R. P. Urbanek. 1997. A reintroduction technique for migratory birds: Leading Canada geese and isolation-reared sandhill cranes with ultralight aircraft. Proc. North Am. Crane Workshop 7: 96–104.
3. Ludders, J. W., J. A. Langenberg, N. M. Czekala, H. N. Erb and H. McCormick. 1998. Serum corticosterone response to adrenocorticotropic hormone stimulation in Florida sandhill cranes. J. Wildl. Dis. 34: 715–721.
4. Ludders, J. W., J. A. Langenberg, N. M. Czekala, H. N. Erb, and H. McCormick. In press. Fecal corticosterone reflects serum corticosterone in Florida sandhill cranes (Grus canadensis pratensis). J. Wildl. Dis. 37 (3).