Peregrine Falcon Recovery in Alaska: What the Genes Show

Young peregrine falcon chicks. NPS / Melanie Flamme.

Background

In the mid-20th century, the pesticide DDT built up in peregrine falcons, thinning their eggshells so they couldn't reproduce. Falcons vanished from parts of North America and Europe, and some populations fell by more than 75%. Some places restored them with captive-bred birds, but falcons in Alaska recovered naturally.

The study

Scientists compared genetic diversity — using microsatellite and mitochondrial DNA — in falcons nesting along the Colville River (Arctic) and upper Yukon River (Interior) across three periods:

They measured heterozygosity, allele numbers and richness, haplotype and nucleotide diversity, private alleles and haplotypes, effective population size, inbreeding, and more. DNA came in part from eggshells.

DNA samples are taken from eggshells. NPS.

Findings

• A short crash: the decline lasted about 10–15 years. Samples from it were few but covered 17.2% (Arctic) and 18.5% (Interior) of known breeding pairs.
• Arctic: shifts in haplotype frequencies, more inbreeding, smaller effective population size, more private haplotypes, and signs of population growth. Numbers stabilized by the mid-1990s — within 10–15 years after 1968, just a few generations — showing how fast genetics can shift.
• Interior: lower haplotype diversity and signs that recovery began with only a few falcons, boosted by immigration. Year-to-year variation in breeding success was about twice the Arctic's, and numbers didn't stabilize until the early 2010s.
• How they recovered: both populations rebounded through recruitment from within and immigration. Falcons dispersing across the landscape kept gene flow going, adding breeders and preserving diversity through the decline.

Sources

Based on "What Genetics Can Tell Us About Peregrine Falcon Recovery," Yukon–Charley Rivers National Preserve, National Park Service, summarizing Sonsthagen, Swem, Ambrose, Flamme, White, Sage and Talbot (2022), "The DDT-induced decline influenced genetic diversity in naturally recovered Peregrine falcons," Ibis; a work of the United States government in the public domain.