Chromatic disorders in bats: a review of pigmentation anomalies and the misuse of terms to describe them

Chromatic disorders in bats are being reported worldwide at an increasing rate. However, there is widespread misunderstanding and misuse of the associated terminology and concepts in the scientific literature. We conducted an extensive assessment and standardisation of published and unpublished cases of chromatic disorders in bats worldwide. Chromatic disorders have been recorded in at least 609 bats belonging to 115 species and 10 families (after correction of misused terms, 152 cases of albinism, 11 of leucism, 269 of piebaldism, 20 of hypomelanism, three of partial melanism and 94 of melanism; a further 60 records remain unclassified). Of the 354 records in which a location was given, 297 bats were found in closed roost sites, mainly caves, buildings, and mines and galleries, while just three were found roosting externally. This difference could be attributed to the greater monitoring effort employed in underground areas than in forests, and to the greater detectability of bats dwelling in caves and buildings than forest- dwelling species. Although reports of chromatic disorders in bats are reasonably well spread around the globe, there are large areas from which no disorders have ever been reported: the Central Amazon, almost all of Africa, northern Europe, and almost all of Asia and Oceania. This is likely to be attributable to either the disregard for information on chromatic disorders (e.g. Central Amazon) or to the low abundance of occurring species (e.g. northern Europe). In all, 40% of the records of leucism and piebaldism were misclassified as ' partial albinism '; leucism was also often used to designate pied aberrations. We propose a standardised classification to distinguish between albinism, leucism, piebaldism, hypomelanism, melanism and partial melanism. Due to frequent confusion, we encourage scientists to follow this classification and we highlight the need to employ comprehensive terminology when describing chromatic disorders in scientific publications.