Chestnut Munia

Frontiers of Taxonomy: Tricolored and Chestnut Munias.

The relationship between Tricolored and Chestnut Munias (Lonchura malacca and L. atricapilla) has been fraught with confusion and some disagreement remains over their taxonomic status.  The ornithological literature lumped them together as the Black-headed Munia (L. malacca) during most of the 1900s.  Since the mid-1990s the trend has been to recognize them as separate, following Robin Restall, who wrote the most comprehensive reference work on munias worldwide (Munias and Mannikins, 1996).  But several sources of confusion remain—most emanate from India, where both species (or forms) are native:

A portion of the Tricolored Munia population is variably intermediate in appearance.  Most of these birds show the pattern of Tricolored but the coloration of Chestnut—and in some cases field identification is difficult.  Individuals that fit this general description apparently occur to some extent throughout Tricolored’s range, but they may be more numerous in areas of potential overlap with Chestnut.  Some of these intermediate birds may be hybrids (or back-cross descendants of hybrids) but most are merely color morphs of Tricolored.

Many authoritative references in India continue to treat Tricolored and Chestnut as a single species.  Some add to the confusion by using the name Tricolored Munia to refer to the collective.  As a result, many observers there do not attempt to differentiate between them in their field observations.

Tricolored Munia has apparently expanded its range north across a broad region of the Indian subcontinent (essentially throughout the Ganges River plain), and now occupies a large area that was formerly occupied by Chestnut Munia, apparently out-competing and replacing it.  As a result, most references to the distributions of the two species do not reflect their current status.

Restall has argued for separating Tricolored and Chestnut Munias based on, among other factors, differences in vocalizations and the gape patterns of nestlings.  As both species are often kept as cage birds, sometimes together in aviaries, Restall also cites the experience of aviculturalists who report that Tricolored and Chestnut self-segregate when given the opportunity.  Assortative breeding has also been reported in the wild in both native and introduced populations.

In addition, the apparent displacement of Chestnut Munias by Tricolored along the Ganges is facial evidence that the two species do not simply blend into a common gene pool when they come into contact.  Instead, it appears that one form out-competes and eliminates the other, which is consistent with their being different species that remain genetically intact and have divergent adaptive success.

The existence of apparently intermediate individuals is the original source of confusion over the status of Tricolored and Chestnut Munias, and it causes three persistent problems.  First, it appears to be facial evidence of hybridization, which suggests that the two are a single species and therefore not reliably distinguishable, so few observers make the effort.  Second, the intrinsic variation within both species is not well depicted in field guides, so there is no adequate reference to help observers reliably identify apparently intermediate individuals.  Third, the lack of clarity leads to inconsistent field identification of those apparently intermediate individuals, so a large portion of observer reports are simply unreliable.

The field identification problem is best solved by a study of the intrinsic variation in both species.  With this knowledge, most clearly observed individuals can be reliably identified.  For an account of their variation and guidance on some consistent distinctions to differentiate them in the field, see above.