Dr. Nial Moores, Birds Korea, April 27th 2014 (edited April 29th)
An image on the Surfbirds website dated April 22nd taken by Max Berlijn shows three Baer’s Pochard Aythya baeri (two males, both with heads showing a hint of chestnut iridescence on a green background, and one female) and a Ferruginous Duck Aythya nyroca. The image was taken in Hebei Province, China, in April this year and comes with the photographer’s comment: "On 22nd and 23rd, we saw at least 26 (Baer’s) in total at this place known to in-crowd people…Some …were mated with males of the commoner Ferruginous Duck."
This is perhaps the highest count worldwide of the now Critically Endangered Baer’s for a couple of years, and will be understood by many as great news. However, seeing Baer’s there paired with Ferruginous, the observer wonders whether hybridisation is "maybe one of the reasons" for the decline of the now Critically Endangered Baer’s.
As part of the fledgling Task Force for the species, we contacted Mr. Berlijn for further information. He informed us (on April 29) that 26 is probably an undercount of birds present as "the lake has vast amounts of reed beds". However, over the two days there he "often" saw mixed pairs (of female Baer’s with male Ferruginous), and encounters in which male Baer’s tried to chase off Ferruginous.
The likely threat of hybridisation between these two species was identified a decade or more ago (at least by Birds Koreans). Since the mid-2000s, observations in the Republic of Korea of apparent hybrids have outnumbered observations of apparently pure Baer’s; and more rarely Baer’s have been seen apparently paired up with Ferruginous. Even a quick google of online images of birds identified as Baer’s in other parts of Asia reveals individuals showing a range of features that are at odds with published descriptions of Baer’s (including reduced white on the foreflank and most especially extensive chestnut on the head). Puzzlingly, despite several communications on the subject, hybridisation is still not included as a likely threat to Baer’s in the BirdLife International Factsheet for the species (at: http://www.birdlife.org/datazone/speciesfactsheet.php?id=478).
The threat of hybridisation is likely to have increased in recent decades and it does seem most likely to be contributing to a decline in "pure" Baer’s Pochard. Ferruginous Duck historically was rare in East Asia and its breeding range apparently did not overlap with Baer’s which nested to the north-east. The region’s changing climate (milder with a shift in rainfall patterns) has led to conditions that seem to favour the north-eastern spread of the globally Near-threatened Ferruginous while reducing the quality of optimal breeding habitat further north needed by Baer’s. Indeed, this single site in Hebei Province visited by Mr. Berlijn now holds the majority of the known world breeding population of Baer’s, even though it lies to the south of the mapped historical range of Baer’s. Hebei also lies toward the northern end of the present range of Ferruginous (even though this is excluded, again puzzlingly, from the map in BirdLife’s Factsheet for that species). Shandong Province (recently suspected also to have breeding Baer’s) lies even further to the south. How many of the Baer’s at these southern sites are unaffected by hybridisation with Ferruginous Duck?
Image One and Two: Encounter between male Baer’s Pochard and apparent mixed pair of female Baer’s Pochard and male Ferruginous Duck, Hebei April 2014. Copyright Max Berlijn. Even in these images, are all the birds pure or does the extent of pale on the flanks of both of the front birds indicate hybrid influence?
Gathering best-information on the species’ distribution (i.e. sharing details of all Baer’s sightings and images with the global Task Force for the species, convened under the East Asian-Australasian Flyway Partnership) and recognising the full suite of threats are of course both essential first steps in developing the most appropriate and effective conservation response.