Vertebrate road kills in a dry forest of Jalisco, Mexico: Is the presence of a Biosphere Reserve important?
In this study we report vertebrate road-killing on a stretch of 41 km along Mexican Highway 200, a federal two-way road used by motor vehicles traveling from Barra de Navidad to Puerto Vallarta, along the coast of Jalisco, in western Mexico. We selected a section of this road so that 21 km of it cross the Chamela-Cuixmala Biosphere Reserve or is directly adjacent to it, flanked by stretches of 10 km on each end which lie outside the reserve. From January 13 to September 30, 2014, we traveled this segment of the road by vehicle two times a week. Additionally, we walked four sections of 8-km each, four times a week. We photographed and removed every vertebrate roadkill and registered several highway and vegetation characteristics in the surroundings of the corpse.
We recorded 3,850 vertebrate roadkills from 160 species of amphibians (2,090), reptiles (807), mammals (670) and birds (283). Of them, 50 species are endemic to the tropical deciduous forests of the Mexican Pacific slope, 33 are categorized as endangered by the Mexican law, 6 are in the IUCN red list, and 13 are reported in the CITES appendices I and II. The univariate statistical tests of the various factors considered against the abundance of roadkills suggest that vegetation type (the pristine forest within the reserve versus other land uses outside of it), visibility (presence of curves and differences in elevation, presence of forest and scrub immediately adjacent to the road) and vehicular traffic and speed were no significantly related to higher mortality (P > 0.05). A multivariate approach did not suggest a statistical significance either. We propose here several hypothesis to explain this lack of significant effect that need to be explored in future studies: (1) we used the vegetation type as a surrogate of the vertebrate diversity at the landscape level, however the presence of forest fragments in the vicinities of the reserve may result in animals traveling to and from the reserve and therefore leveling the abundance and diversity along the whole stretch of the road we examined, (2) the carelessness of drivers about killing animals or even killing on purpose some species as snakes and felids make the straight sections of the road as dangerous to animals as stretches with lower visibility, and (3) a need to extend the scale of the study to sections farther away from the reserve and its influence.