Genetic study assesses the amount genetic mixture between both species.
Hybridization can lead to extinction. When an endangered species hybridizes with a closely related species, it might get absorbed into that species. There are several examples of rare bird species being threatened by hybridization, such as the Chinese Crested Tern (Thalasseus bernsteini) and Golden-winged Warbler (Vermivora chrysoptera). A recent study in the journal Biological Conservation assessed the situation of the endangered Milky Stork (Mycteria cinerea) in Singapore.
The Milky Stork occurs in coastal mangroves, mudflats and estuaries across Southeast Asia. There are currently about 1500 wild individuals left and the population is declining due to hunting and habitat destruction. In addition, Milky Storks might be interbreeding with their sister species, the Painted Stork (M. leucocephala). This adds another problem to the already precarious situation of this endangered species.
In the Malay Peninsula, Milky Storks have been held in captivity since the 1980s. Unintentionally, hybridization with Painted Stork occurred in these captive populations. A few hybrids escaped into the wild and have possibly interbred with wild birds. To quantify the influence of hybridization on the wild Milky Stork populations, Pratibha Baveja (National University of Singapore) and her colleagues genotyped several individuals using RADseq. The results are worrisome.
The researchers write that “the majority of sampled individuals carried a signature of different degrees of introgression from Painted Storks.” In other words, hybrids have become an integral part of the wild Milky Stork populations. The genetic analyses revealed 18 “pure” Milky Storks and 3 “pure” Painted Storks. The remaining 25 individuals had different proportions of genetic material from both species.
The genomic transition from Milky Stork to Painted Stork is mirrored by morphological traits, such as the presence of pink wing coverts (a trait of Painted Stork). These morphological cues can help detect and remove hybrid individuals from the population. And this removal has to happen quickly, because the authors conclude that “the genomic composition of the Milky Storks in Singapore is highly compromised by hybridization, and immediate conservation action is warranted.”
Baveja, P., Tang, Q., Lee, J.G.H. & Rheindt, F. (2019) Impact of genomic leakage on the conservation of endangered Milky Stork. Biological Conservation, 229:59-66.
This paper has been added to the Ciconiiformes page.