- Researchers in Nepal say they still don’t know what was behind a massive flock of some 7,500 woodpigeons observed in the country’s plains last December.
- A recently published study suggests a range of factors, from food availability to predator avoidance, combined to bring together the flock, which was 25 times larger than the biggest flock previously observed here.
- Climate factors may also have played a part, particularly the impact of heavy rains on the birds’ overwintering grounds in Pakistan.
- Researchers say more studies are needed to get to the bottom of the mystery, and plan to watch out for another super flock this coming winter.
Three reasearchers in Nepal, Hiru Lal Dangaura, Vikram Tiwari and Subam Chaudhary, were conducting a routine check on a vulture colony in the western plains of Nepal in December 2022. They witnessed an extraordinary spectacle here: a huge flock of pigeons. The swarm that stretched across the sky formed a dynamic canvas of gray and white. The air filled was with the rhythmic flapping of wings and the soft cooing of the birds, the researchers recall.
The discovery of the flock, estimated at some 6,500 pigeons on December 14, and 7,500 the next day, has been touted as a rare phenomenon that has puzzled local researchers and bird-watchers alike, Dangaura and his colleagues wrote in a recently published study in the Nepalese Journal of Zoology.
“We had never encountered such a large assembly of pigeons in our careers,” Dangaura, a project field officer at the NGO Bird Conservation Nepal (BCN), told Mongabay.
The observation coincided with the period when in the plains started irrigating their land for their winter wheat crop.
“When water enters the fields, bird prey such as worms and insects come to the surface. The pigeons we saw were feeding on those types of prey,” Dangaura said.
The flock was made up of the South-Central Asian subspecies of the common woodpigeon, Columba palumbus casiotis, which the study authors identified from the birds’ cinnamon-coloured neck. Woodpigeons aren’t considered a threatened species, since they occur in large numbers across a broad range, from Europe to West Asia and North Africa. In Nepal, the pigeon is a migratory species, and has routinely been spotted during the winter.
“However, we had never seen a flock this big,” said ornithologist Krishan Prasad Bhusal, who wasn’t involved in the study.
“The high count of this species observed by our team exceeds any known reports for this subspecies,” the study authors noted. The previous biggest flock observed by ornithologists in Nepal was around 300.
For this particular subspecies, the size of the flock is unprecedented across its range in this part of the world, the study said. Other significant observations of the species, which the authors obtained from the citizen-science platform eBird, showed flocks of about 500 pigeons in India and 250 in Pakistan. Smaller flocks were recorded in southern Iran (40) and northeastern Iran (100).
The European subspecies, C. p. palumbus, however, has been observed in massive flocks of around 50,000 birds, said study co-author Anand Chaudhary. He added he believes the birds they saw in Nepal’s plains were likely on the Central Asian Flyway, the migration route used by large numbers of birds to overwintering and breeding grounds throughout Eurasia, the Arctic Ocean, the Indian Ocean and the associated island chains.
Various factors such as food availability, weather conditions, predator avoidance and social attraction may have led to such a large number coming together at once as they passed through Nepal, Chaudhary said.
“We don’t know [for certain] what brought the flocks in such numbers to Nepal,” he said. “There hasn’t been much research into how these birds use the flyway.”
Dangaura said that changes in climatic and environmental variables such as wind patterns and precipitation due to warming of the planet could have been a factor.
“We also considered possibilities such as the massive floods that took place in Pakistan in the summer of 2022,” the study authors said. Although most of the flood-hit areas aren’t wintering grounds for the woodpigeon, their habitats may have been affected by heavy rainfall spread across the country, the study says.
“However, to correlate the Pakistan floods to common wood pigeon irruption in Nepal is no more than speculative,” it notes. It adds such migrations may be common for the subspecies, but may not have been recorded previously due to a limited number of bird-watchers and ornithologists in the South and Central Asian region.
Chaudhary said the results call for greater effort to monitor and conserve birds along the Central Asian Flyway and assess the potential impacts of climatic factors.
However, Bhusal said he doubts the pigeons were on the Central Asian Flyway, which he noted is frequented by waterbirds and birds of prey such as vultures. He agreed, though, that more research is needed to clear up the question.
Meanwhile, Dangaura and his team are eagerly awaiting the arrival of the coming winter to see if the pigeons return in huge numbers like last year. They tried to count them the last time around, he said, and this time plan to get a better understanding of what’s actually going on.
Dangaura, H. L., Tiwari, V., Chaudhary, S., Dangaura, K. D., & Chaudhary, A. (2023). Record numbers of common wood pigeon (Columba palumbus casiotis) observed in western Nepal during December 2022. Nepalese Journal of Zoology, 7(1), 60-64. doi:10.3126/njz.v7i1.56311
This article was first published on Mongabay.com.
Banner image: A common wood pigeon (Columba palumbus casiotis). Photo by Andrew Bazdyrev/iNaturalist (CC BY 4.0).