North American Crane Working Group

 

Date of this Version

2001

Document Type

Article

Citation

Lewis, James C. Increased egg conservation--is it essential for recovery of whooping cranes in the Arnasas/Wood Buffalo population? In: Ellis, David H., ed., Proceedings of the Eighth North American Crane Workshop, 11–14 January 2000, Albuquerque, New Mexico (Seattle, Wash: North American Crane Working Group, 2001), pp. 1-5.

Comments

Reproduced by permission of the North American Crane Working Group (NACWG).

Abstract

The whooping crane (Grus americana) is in a race for survival against adversities (genetic, demographic, and environmental) that are only partially understood. There is increasing evidence of genetic problems (drift, inbreeding, and loss of heterozygosity) in the captive population that likely also exist in the wild Aransas-Wood Buffalo Population (A WP), a consequence of the 1940s population bottleneck. Small populations are vulnerable to extinction through catastrophic events and random changes in productivity or survival. Negative environmental effects faced by whooping cranes include upstream diversion which diminish freshwater (nutrient) inflow into Texas wintering habitats, and expanding human activities along the coast of the Gulf of Mexico. Population and genetic specialists tell us that security against genetic problems, demographic fluctuations, and environmental changes, lies in maximizing population size. An appropriate minimum population goal to overcome the aforementioned problems is 1,000 individuals (Shaffer 1981, Salwasser et al. 1984, Mirande et al. 1993). The Canadian- United States Whooping Crane Recovery Team has accepted 1,000 birds as their goal for the A WP. If habitat is not limiting and inbreeding does not depress viability (rather large uncertainties), another 30+ years must pass before the A WP reaches 1,000 individuals (Mirande et al. 1993). Can the A WP survive 30+ years to reach a minimum secure population level? It seems evident that managers should be cautious and consider what might be done to accelerate A WP growth. Two potential techniques come to mind. One would be to supplement the population with introductions of captive-reared cranes. In previous brief discussions by the recovery teams, this approach has been discounted because of potential disease transmission to the only wild self-sustaining population. The second technique would be to initiate intensive egg management (Fig. 1) as described by Ellis and Gee (2001).