A putative hybrid between Cattle Egret and Little Egret

Observational evidence for a peculiar hybrid.

In 2012, Ali Gholamhosseini and his colleagues showed that avian hybridization occurs more often between sister species than between non-sister species, providing “support for a long-assumed but previously untested assumption”. Indeed, hybridization is more likely between closely related species that belong to the same genus. Occasionally, an intergeneric hybrid pops up. In a recent Waterbirds paper, Japanese researchers reported a peculiar cross between Cattle Egret (Bubulcus ibis) and Little Egret (Egretta garzetta). Let’s have a look at the evidence.

The putative hybrid between Cattle Egret and Little Egret. From: Komura et al. (2023)

Intermediate Morphology

In July 2020, birdwatchers came across a remarkable Egret in a paddy field near Hashima City (Japan). At first, the bird was considered a partially melanistic Little Egret. But more detailed observations raised the possibility of hybridization. Specifically, the bird showed characteristics of both Cattle Egret and Little Egret.

Because the researchers could not capture the potential hybrid, they relied on pictures to estimate several morphological traits. Tarsus length was determined by comparing the size of the bird with a stone post on which it perched. And bill morphology could be assessed by dividing the bill length and the bill depth, resulting in a “r-value” that could be compared with the putative parental species. Both the tarsus length and the r-value showed intermediate values between Cattle Egret and Little Egret.

The r-value – calculated by dividing the bill length (BL) by the bill depth (BD) – of the hybrid was intermediate between Cattle Egret and Little Egret. From: Komaru et al. (2023).

More Data

The intermediate traits definitely suggest hybridization between Cattle Egret and Little Egret. Indeed, hybrids often exhibit intermediate morphology, such as the captive crosses between Chiloé Wigeon (Mareca sibilatrix) and Philippine Duck (Anas luzonica) which I covered in this blog post.

However, more evidence – preferably based on genetic data – is needed to confirm hybridization. At the end of the paper, the researchers indicate that they plan to “collect more data, such as DNA data, for further analysis.” Hopefully, they will manage to assess the genetic make-up of this remarkable bird. I am very curious to learn whether it really is an intergeneric hybrid.

References

Komaru, K., Tanaka, S., & Moribe, J. (2023). A Natural Hybridization between a Cattle Egret (Bubulcus ibis) and a Little Egret (Egretta garzetta) in Japan. Waterbirds, 45(4), 497-501.

Featured image: The putative hybrid egret © Kanade Komaru | Waterbirds