# Es Colomer, a Unique Population of the Lilford’s Wall Lizard, Podarcis lilfordi (Squamata: Lacertidae)

## TL;DR

A unique population of melanistic Lilford’s Wall lizards on Colomer Island shows extreme traits like high density, aggression, and omnivorous diet due to harsh environmental conditions.

## Contribution

The study presents new insights into the ecology and behavior of a melanistic, high-density lizard population on a small Mediterranean islet.

## Key findings

- The Colomer population has the highest recorded density of Lilford’s Wall lizards.
- Males show higher rates of digit amputations, likely due to frequent aggressive interactions.
- The lizards have an omnivorous diet including carcasses and even conspecifics.

## Abstract

Colomer Island (northwest coast of Mallorca Island, Balearic Islands, Spain) is inhabited by an extraordinary population of the Lilford’s Wall lizard, Podarcis lilfordi, an endemic species of Balearic Islands that today is only present on the coastal islets of Mallorca, Menorca and Cabrera archipelago. The Colomer Wall lizards were discovered almost 100 years ago but have only been studied in the field since 2006. This is a population of melanistic lizards, with a marked sexual dimorphism in several characteristics such as body size, tail length and head size. The density of lizards is very high. In 2024 we recorded the highest known density of lizards in this species. This remarkable abundance promotes the existence of frequent aggressive interactions between males, a high parasite load and a foraging ecology that includes a large variety of prey, plant matter, carcasses from birds and mammals, and even conspecifics. All these traits are considered an adaptation to the extreme environmental conditions of this small Mediterranean islet.

Es Colomer Island is occupied by a melanistic population of the Lilford’s Wall lizard, Podarcis lilfordi. Adult males are larger than females, with longer tails, and higher values of body mass, pileus length, head heigh, head width, hindleg length and number of dorsal scales. Adult sex ratio is balanced or slightly skewed towards males. At the summit of the islet, body condition was found to be significantly better than in almost vertical slopes. We found a higher proportion of digit amputations in adult males, probably due to frequent male–male interactions, promoted by high lizard density. During a 2024 survey, we recorded the highest known density of the Lilford’s Wall lizard. The prevalence of mites and blood parasites was 100%. The frequent intraspecific interactions, shown by the proportion of males with digit amputations, could be the source of the higher prevalence and susceptibility to blood parasite infections. The diet of lizards from Colomer is omnivorous, including several prey groups, as well as carcass remains from birds and mammals, and even conspecifics. Lizards from Colomer are an excellent example of the effects of extreme environmental conditions, with high population densities, strong intraspecific competition, the widespread presence of external and blood parasites, the extensive use of the scarce resources, and the opportunistic use of unpredictable resources in masting years, such as the fruits of the joint pine.