The research, conducted between 2011 and 2025 across three ornamental waterfowl collections in the villages of Voyvodinovo, Pancharevo and Chintulovo, Bulgaria, recorded crosses between species that would almost never encounter one another in nature. Of the five hybridisation events, four involved intergeneric crosses — pairing birds from entirely different genera — while one was an intrageneric cross within the genus Spatula. The findings confirm that when natural reproductive barriers are removed, waterfowl are capable of producing viable offspring with significant phenotypic and genetic variability.

The first documented case dates back to 2011, when a male Hottentot teal (Spatula hottentota) crossed with a female Silver teal (Spatula versicolor) in the same genus. The resulting hybrid male reached advanced developmental stages and displayed a fascinating split inheritance pattern. Its body size matched the maternal Silver teal, being significantly larger than the paternal form, yet its plumage colouration strongly favoured the Hottentot teal father. The bill lacked the yellow basal spot and the white rump plumage characteristic of the Silver teal mother, while the hybrid also differed from its father by the absence of the black triangular patch within the white facial area and by a notably darker black crown.

In 2018, a more dramatic cross occurred between a male Ferruginous duck (Aythya nyroca) and a female Mandarin duck (Aix galericulata) — two species from different genera with markedly different body structures. From a clutch of nine eggs, three individuals hatched and two survived to maturity: one male and one female. The hybrids exhibited a pronounced phenotypic resemblance to the paternal Ferruginous duck, with a clear dominance of its morphological characteristics. Both sexes inherited the elongated body structure of the Mandarin duck rather than the robust, rounded form of the Ferruginous duck, yet their plumage followed the father’s expression. The male hybrid featured the light iris consistent with the Ferruginous duck, though it displayed a slight darkening of the head and grey flank feathers atypical for the paternal species. The female hybrid mirrored the paternal colouration but lacked the white patch under the bill and the white triangles on the wing speculum.

The third case, recorded in 2020, involved a male Brazilian teal (Amazonetta brasiliensis) and a female Ringed teal (Callonetta leucophrys). A clutch of six eggs was laid between 16 and 24 June 2020, with hatching recorded on 20 July. Although six ducklings hatched, three perished at just two days old, while the remaining three — all male — reached maturity. The surviving hybrids exhibited predominantly paternal characteristics regarding size and colouration, with body and head colouration strongly resembling the Brazilian teal father. Maternal influence was evident only in the bill colouration, which was blue in two hybrids and black in the third, while the legs were pink rather than the vivid scarlet red typical of male Brazilian teals.

Two separate hybridisation events were documented in 2025. The first involved a male Chestnut teal (Anas castanea) and a female Wood duck (Aix sponsa), producing two male hybrids with intermediate characteristics, although the paternal phenotype appeared dominant. The heads of both hybrids were dark-coloured — a trait shared by both parental species — but the distinctive white facial markings characteristic of the Wood duck were absent. The bill structure resembled that of the Wood duck but was significantly darker, reflecting the paternal influence of the Chestnut teal. Two female hybrids were also identified, which phenotypically closely resembled the paternal species in head and body plumage, while the morphology of their bills and the presence of a pale patch beneath the bill were characteristic features of female Wood ducks.

The final 2025 case involved a male Baikal teal (Sibirionetta formosa) and a female Falcated duck (Mareca falcata). Two individuals hatched — one male and one female — both demonstrating traits characteristic of both parental species, consistent with an intermediate inheritance pattern. The male hybrid strongly resembled the paternal Baikal teal, except that the facial markings and colour zones were not clearly differentiated, with a blending of colours from the breast towards the flanks lacking the distinct white vertical line of the paternal species. The female hybrid inherited more traits from the male parent yet lacked the white spot at the base of the bill and exhibited a larger body size consistent with the Falcated duck.

The synthesised results demonstrate that successful mating occurred in all observed cases, with viable offspring produced in the majority of instances. Phenotypic analysis reveals that paternal traits predominated in most hybrids, though intermediate inheritance was also noted in specific pairings. This consistent paternal dominance may be attributed to specificities in genetic regulation or to asymmetry in the inheritance of certain traits, including those related to colouration and sexual dimorphism. However, the researchers caution that the interpretation of inheritance patterns is based primarily on phenotypic observations, and that trait expression may also be influenced by sex-linked inheritance, epigenetic mechanisms, incomplete dominance or environmental factors.

From a conservation perspective, the findings carry significant implications. The artificial overcoming of behavioural and ecological barriers in captivity facilitates interspecific hybridisation within the order Anatidae, underscoring the risk of genetic swamping and introgression into wild populations should such individuals escape. Uncontrolled crossing of ducks in captive collections diverts valuable resources away from scientifically managed ex-situ conservation programmes aimed at preserving genetically pure and threatened taxa. As key traits such as plumage structure and colouration in ducks are often determined by complex polygenic interactions and epistasis, relying solely on morphological assessment limits the accurate determination of parental contribution. Future studies combining phenotypic analysis with molecular markers would help validate parental dominance and clarify the underlying genetic architecture of hybrid individuals, ensuring that careful management of mixed-species collections balances scientific research objectives with long-term conservation goals.

Subject of Research: Hybridisation between different species of waterfowl

Article Title: Hybridisation between different species of waterfowl

Article References: Petrov, R., & Nikolov, S. (2026). Hybridisation between different species of waterfowl. Biodiversity Data Journal, 14, Article e197937. https://doi.org/10.3897/bdj.14.e197937

Image Credits: AI Generated

DOI: 10.3897/BDJ.14.e197937

Keywords: waterfowl, hybridisation, ducks, teals, captive breeding, genetic integrity, between, different, species, scientific research