After the Cats Were Gone, the Birds Returned<\/p>\n
The Ogasawara Islands, a UNESCO World Heritage Site<\/a>, have long been plagued by invasive species<\/a>. Among the most destructive: feral cats, introduced over decades of human activity. By the 2000s, the red-headed wood pigeon, which nests close to the ground and is endemic to this archipelago, was nearing extinction.<\/p>\n Between 2010 and 2013, conservation teams captured and removed 131 cats from Chichijima, one of the islands in the chain. The results were fast and clear. The number of adult pigeons soared from 111 to 966, and juveniles jumped from 9 to 189, as reported in Communications Biology<\/a>.<\/p>\n Unlike many endangered species, the pigeons didn\u2019t collapse under the weight of genetic bottlenecks or loss of diversity. Instead, they appeared to thrive.<\/p>\n Genetic Purging May Have Changed the Rules<\/p>\n In most small populations, inbreeding leads to accumulation of harmful mutations, reducing survival and reproductive success. But the red-headed wood pigeon defied that rule. Genomic sequencing by a team from Kyoto University revealed that these birds carried fewer nonsense mutations\u2014genetic defects that disrupt protein function\u2014than their more genetically diverse mainland relatives, the Japanese wood pigeon<\/a>.<\/p>\n More than 80% of the island pigeons\u2019 genome was homozygous\u2014an indicator of inbreeding usually associated with extinction risk. Yet, individuals with higher inbreeding levels in captivity often lived just as long\u2014or longer\u2014than others.<\/p>\n This suggests a phenomenon known as genetic purging. Over many generations, harmful mutations may have been systematically removed from the gene pool. The result: a population with low genetic diversity, but also a surprisingly low genetic load.<\/p>\n \u201cMost conservation models assume small populations are always vulnerable due to genetic deterioration,\u201d said Dr. Daichi Tsujimoto, lead author of the study<\/a>. \u201cBut what we found suggests that, under certain long-term conditions, small populations can actually adapt to survive.\u201d<\/p>\n Not Just a Fluke\u2014Other Island Survivors Show the Same Pattern<\/p>\n The red-headed wood pigeon isn\u2019t the only species that appears to have \u201cpurged\u201d its genetic baggage. Similar patterns have been documented in other island-endemic animals. The island fox (Urocyon littoralis)<\/a>, native to California\u2019s Channel Islands, rebounded from near extinction with minimal signs of inbreeding-related problems.<\/p>\n![\"Distribution](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2025\/12\/Distribution-and-population-history-of-the-critically-endangered-red-headed-wood-pigeon-Columba-jant.jpeg\"\/)
Distribution and population history of the critically endangered red-headed wood pigeon (Columba janthina nitens) and the widespread Japanese wood pigeon (C. j. janthina). Credit: Communications Biology<\/p>\n![\"\u6587\u7ae0\u3092\u5165\u308c\u3066\u304f\u3060\u3055\u3044\"](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2025\/11\/2508_main_isagi-c120bf294c9e23e83603755e231e65d6.jpg\"\/)
The red-headed wood pigeon, a critically endangered species endemic to the Ogasawara Islands, Japan. Credits: KyotoU \/ Daichi Tsujimoto<\/p>\n
![\"Northern](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2025\/12\/Northern-elephant-seal-population-growth.-Estimated-population-sizes-are-represented-by-the-diamonds.jpeg\"\/)
Northern elephant seal population growth. Estimated population sizes are represented by the diamonds. Credit: Journal of Heredity<\/p>\n![\"Japanese](\"https:\/\/www.newsbeep.com\/au\/wp-content\/uploads\/2025\/12\/Japanese-wood-pigeon-1200x900.jpeg\"\/)
The Japanese Wood Pigeon. Credit: Kasia & Takashi Someya<\/p>\n