Genetic Diversity Among Ferruginous and Swainson's Hawks: An Interdisciplinary Interpretation
Date
1997
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Masters
Abstract
Ferruginous hawk (Buteo regalis) populations and breeding range have declined since prairie settlement. Concern over this downward trend led the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) to list ferruginous hawks as "threatened" in 1980. Current populations appear to have stabilized within the reduced range and ferruginous hawks were downlisted to "vulnerable" in 1995. While stable populations are positive for hawk conservation, genetic diversity may have been negatively impacted by hawk population declines and changes in distribution. Loss of genetic diversity may reduce a population's chances of long-term survival by increasing frequencies of harmful alleles or by reducing the genetic capacity of a population to adapt to environmental changes. I assessed genetic diversity among ferruginous hawks from seven sites in prairie Canada and Idaho, U. S. A. using DNA fingerprinting. I also analyzed DNA from Swainson's hawks (Buteo swainsoni), a widespread and more numerous prairie hawk. Unlike ferruginous hawks, Swainson's hawks did not undergo large population or range reductions during settlement. Therefore they serve as a useful species with which to compare ferruginous hawks.
High Average Percent Differences (APD's) in band sharing and heterozygosity estimates from DNA fingerprints indicate a high genetic diversity among sampled populations of both ferruginous and Swainson's hawks. Ferruginous hawk APD and heterozygosity estimates were similar to
both Swainson's hawk estimates and those reported for other bird species with large stable populations.
I also assessed population subdivision (Dij) to determine whether hawks interbred among the sample sites. I found slight population subdivision between Hanna and Southwest Alberta ferruginous hawks (Dij = 0.06 ± 0.04, Median test, p<0.025). The most likely explanation for this observation is a local extirpation event (possibly in SW Alberta) followed by recolonization with a small number of hawks. Some level of subdivision could be established through inbreeding and maintained through philopatry. This subdivision is slight compared to published reports in which APD's are noticeably higher between subdivided populations. I detected no population subdivision among all other ferruginous and Swainson's hawk sites suggesting that interbreeding, through natal and/or breeding dispersal, is occurring throughout the range.
Current genetic diversity is unlikely to limit long-term persistence of ferruginous hawk populations. The future range and population size are
likely determined by human social and economic decisions that affect land use patterns on the prairies.
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Degree
Master of Science (M.Sc.)
Department
Biology
Program
Biology