Half in One Sanctuary
Mexico's overwintering region includes 12 traditional wintering sites. Half of this year's butterflies are residing in only one site, the El Rosario sanctuary.

This means that half of our continent's migratory monarchs in Mexico are clustered together in an area the size of 1.5 football fields. The fact that the monarchs are so concentrated puts them at increased risk.

Compare Years
How does this year compare to previous years? These pie charts shows monarch distribution over 6 years. This column chart compares the number of monarchs per site per year. Notice how few sites the monarchs used: 80% of the monarchs were concentrated in only 1-4 sites.

Site Selection and Survival
Scientists don't fully understand what drives site selection. Some habitat variables include:

• forest quality
• available space
• access to water
• exposure to sun, moisture, wind
• level of human disturbance

High quality habitat in Mexico is critical for monarch survival. Site selection comparisons guide conservation strategies and priorities.