# Status of the Mule Deer Population in Western Sonora, Mexico

## TL;DR

This study estimates the population and structure of mule deer in western Sonora, Mexico, finding a stable population but with low fawn numbers.

## Contribution

The first large-scale population survey of mule deer in western Sonora, revealing insights into population stability and recruitment.

## Key findings

- Aerial surveys observed 1376 mule deer with a male:female:fawn ratio of 24:100:12, indicating a stable population.
- Areas with high deer numbers coincided with Wildlife Conservation Management Units where habitat improvements are implemented.
- Low fawn proportion suggests potential recruitment limitations despite overall population stability.

## Abstract

The conservation status of mule deer in the state of Sonora, Mexico, remains unclear because no large-scale monitoring of the species’ population has yet been carried out. This study estimated the relative abundance and population structure of mule deer in western Sonora. Aerial surveys were conducted from 4 to 24 November 2019, using linear transects distributed across 62 sampling quadrants (30 × 30 km each) in western Sonora. During 82 flight hours, a total of 1376 deer were observed, with a male:female:fawn ratio of 24:100:12. This is a ratio of age and sex classes that falls within the limits of a stable population of desert mule deer, although the low proportion of fawns suggests potential limitations on recruitment. On the other hand, the quadrants with the highest numbers of deer tended to coincide with areas containing a high concentration of Wildlife Conservation Management Units, where habitat improvement actions are implemented. The findings highlight the importance of continued habitat management and monitoring to support population stability and long-term conservation.

The mule deer population in Mexico declined severely during the early 20th century but recovered due to public policies centered on sport hunting. Sonora is considered the main reference for mule deer management in Mexico; however, the conservation status of the species in the state remains unclear. This study aimed to estimate the relative abundance and population structure of mule deer in Sonora. An aerial survey was conducted from 4 to 24 November 2019 using linear transects distributed across 62 sampling quadrants (30 × 30 km each). Over 82 flight hours, a total of 1376 deer were observed, with a male:female:fawn ratio of 24:100:12. The number of sightings and deer observed per quadrant followed a normal distribution, with averages of five sightings and twenty-two deer per sampling unit. The quadrants with the lowest abundance corresponded to areas containing towns and agricultural fields, whereas the areas with the highest deer numbers coincided with those containing a high concentration of Wildlife Conservation Management Units, where habitat improvement actions were implemented. The results falls within the limits of a stable population of desert mule deer; however, the low proportion of fawns suggests that limiting factors may be exerting pressure on the population. These findings highlight the importance of continued habitat management and monitoring to promote population stability and support recruitment in Sonoran mule deer populations.