Abstract

Alpha-chloralose, a chloral derivative of glucose which depresses the cortical centers of the brain¹, is regularly used orally in bait to capture wild cranes^2,4. The physiologic effects of alpha-chloralose and this method of capture are not well described. Capture myopathy is not uncommonly seen in cranes,^3,5 and has been diagnosed in cranes dying after capture with alpha-chloralose. The goals of this study are (1) to document the physiologic effects of alpha-chloralose capture of wild cranes, and (2) to investigate whether there are clinico-pathologic parameters measurable at the time of capture which can predict which birds are at highest risk to develop capture myopathy.

From 1996–1997, 44 greater sandhill cranes (Grus canadensis tabida) were captured in central Wisconsin using alpha-chloralose for ecologic and disease research. Individual families were habituated to regularly come to whole corn bait stations, and then alpha-chloralose was mixed into the bait at 0.37–0.43g/cup of corn (approximately 0.16–0.21 g/crane), depending on the ambient temperature. Cranes could generally be approached and restrained within 1–2 hr after they began feeding. Hoods and body wraps were used during transport and sample collection and banding procedures, which on average required 1 hr. The cranes were held in a small pen in the field during recovery, and were released from 8–22 hr after capture. In 1996, capture myopathy was diagnosed in one of the captured cranes who was unable to stand the day after capture; it was rehabilitated and successfully released.

In 1997, physiologic monitoring was done on 18 adult sandhill cranes at the time of capture, at the time of banding (1 hr later), 8 hr after capture, and at the time of release (22 hr after capture). Core body temperature, heart rate, and respiratory rate were monitored along with subjective scoring for depth of sedation. Venous blood gas parameters (pH, pCO₂, pO₂, Na, K, iCa, PCV, Hb, base excess, HCO₃, tCO₂, sO₂) were serially measured using a hand-held analyzer (i-STAT, Sensor Devices, Inc., Waukasha, WI, USA). Selected serum enzymes and electrolytes were tested 1 hr after capture and at the time of release. Tables 1 and 2 present the results.

Table 1. Physiologic data following alpha-chloralose capture of wild adult sandhill cranes

*Two cranes were released at 8 hr post-capture

Table 2. Serum chemistry data following alpha-chloralose capture of wild adult sandhill cranes

*Two cranes were released at 8 hr post-capture

When compared with reference ranges established in captive sandhill cranes, these results do not suggest that the metabolic acidosis associated with capture myopathy is occurring. The highest serum creatine phosphokinase (CK) levels measured 1 hr and 22 hr after capture were in cranes judged to be lightly sedated; the few more heavily sedated cranes had low CK values.

Literature Cited

1.  Balis G, R Monroe. 1964. The pharmacology of chloralose. Psychopharmacologia. 6: 1–30.

2.  Carpenter J, N Thomas, S Reeves. 1991. Capture myopathy in an endangered sandhill crane (Grus canadensis pulla). J. Zoo. Wildl. Med. 22: 488–493.

3.  Bishop M. 1991. Capturing cranes with alpha-chloralose (an oral tranquilizer). In: Proceedings of the 1987 International Crane Workshop. International Crane Foundation, Baraboo, Wisconsin, Pp. 247–253.

4.  Nesbitt S. 1976. Capturing sandhill crane with oral tranquilizers. In: Proceedings of the 1975 International Crane Workshop. Oklahoma State University Publ., Stillwater, Oklahoma, Pp. 296–298.

5.  Windingstat R, S Hurley, L Sileo. 1983. Capture myopathy in a free-flying greater sandhill crane (Grus canadensis tabida) from Wisconsin. J. Wild. Dis. 19: 289–290.