Genetic variation was lost, but no distinct mitochondrial lineages disappeared.
There used to be about 1.6 million Red-cockaded Woodpeckers (Dryobates borealis) in the southeastern United States. Their numbers dwindled when humans started changing the habitat (e.g., timber harvesting). The population decreased to less than 10,000 birds in 1978, after which it became one of the first species to be protected under the US Endangered Species Act. The implementation of management plans stabilized the population and eventually resulted in increasing numbers. By the early 2000s, there were approximately 14,000 woodpeckers hammering away. A recent study in the journal Ecology and Evolution reconstructed the genetic legacy of these population dynamics.
Mark Miller and his colleagues compared the genetic variation of Red-cockaded Woodpeckers from three time periods: before 1970, 1992-1995 and 2010-2014. The analyses showed that several mitochondrial variants (so-called haplotypes) have been lost over time. However, these variants did not represent distinct evolutionary lineages. It mainly concerned small offshoots of the most common variants. All in all, not much mitochondrial variation was lost.
The genetic diversity was similar in 1992-1995 and in 2010-2014, suggesting that little variation was lost between these time periods. This indicates that the management practices are bearing fruit. The population is recovering, not only in numbers but also in genetic diversity. However, the population structure did chang over time. Before 1970, the woodpecker population was panmictic; there were no identifiable subpopulations. The present study found low levels of population differentiation, suggesting that some subpopulations are relatively isolated from one another. This is probably a consequence of habitat fragmentation. Human impact has clearly left its mark in the genetic make-up of the Red-cockaded Woodpecker.
Miller, M.P., Vilstrup, J.T., Mullins, T.D., McDearman, W., Walters, J.R., & Haig, S.M. (2019). Changes in genetic diversity and differentiation in Red‐cockaded woodpeckers (Dryobates borealis) over the past century. Ecology and Evolution, 9(9):5420-5432.