Identification of Hybrid Birds and Photography

In the age of genomic screening, morphological identification via photography of bird hybrids is still relevant.

Hybridization is the interbreeding of species. Over 10% of bird species have hybridized at least once¹. Human activities can cause hybridization that does not occur in nature. One of the most common form of hybrid is the domestic chicken, Gallus gallus domesticus, with the Red Junglefowl, Gallus gallus, its ancestor. Gallus gallus is arguably the most important bird in the world, due to its role in originating a food source (eggs and meat). The Red Junglefowl Gallus gallus has been said to have been profoundly affected by introgression of the domestic chicken species so that no purely “wild” species exist². The degree of mix exists on a spectrum. The most accurate test to determine admixture between the two species is genetic screening. However, there remains a strong correlation with genetic profiles and external morphology³ (biological form of the animal). Genetic screening is costly and slower, in comparison to visual morphology checks, supported by photography. A hybrid index¹ may be used, which scores traits from one potential species to another. Both morphology and genetic markers can be used to develop the hybrid index.

Another example of the usefulness of photography is the identification of Milky Stork and Painted Stork hybrids. There are approximately 1,500 Milky Storks in the world, 7% to 10% of which are found in the state of Johor, Malaysia and the country of Singapore⁵. In the 1980’s in Singapore, both Milky Storks Mycteria cineria and the more numerous Painted Stork Mycteria leucocephala were kept in captivity in the same enclosures, which caused interbreeding⁵. Some Painted Storks (and hybrids) escaped and were not recovered. These feral storks interbred with wild Milky Storks causing the Milky Stork species to be genetically swamped⁶. The Milky Stork suffers from a risk of extinction, already exacerbated by habitat loss⁵, also caused by human activity.

The count of Milky Storks and hybrids can be facilitated through citizen science, with photography and GPS location. Characteristics of both species and hybrids can be identified through photography, see Figure 2 and 3, with clear hybrids identified in Figure 4.

The risks of hybridization can result in wild species becoming tame (in the case of the domestic chicken). It can also result in reduced biodiversity caused through reduction of species numbers and possible future extinction, as in the case of the endangered Milky Stork. Reduced biodiversity can reduce habitat resilience⁷. In the example of the Milky Stork and Painted Stork, there are subtle differences in diet and foraging⁸. These include the type of prey, including the size of fish, and foraging techniques (probing in sediment or swilling the water with a partially open bill, see video of feeding behaviour in Figure 5.). These differences, and the predominance of one species over another, can impact natural habitats.

By knowing the location and numbers of Milky, Painted and hybrid storks, steps can be taken to protect the remaining threatened species. These steps include protection and segregation⁶, to promote the continued survival of Milky Storks in the wild.

References:

[1] Lovette, I. J. (2017). Chapter 3 How Birds Evolve. In Handbook of bird biology. Section 3.4 Hybridization (pp. 88–92). Ithaca, NY: Cornell lab of ornithology.

[2] Lawler, A. (2012). In search of the wild chicken. Science, 338(6110), 1020–1024.

[6] Baveja P; Tang Q; Lee J.G.H.; Rheindt F.E., “Impact of genomic leakage on the conservation of the endangered Milky Stork” Biological Conservation Volume: 229 Pages: 59–66. DOI: 10.1016/j.biocon.2018.11.009. Published: 2018.

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