Overwintering Site Selection


The Basics of Selecting an Overwintering Site

Each overwintering season, volunteers are asked to monitor a minimum of one monarch overwintering site during the Western Monarch Thanksgiving Count and New Year’s Count. All volunteers need to confirm their sites with a regional coordinator before monitoring. Volunteers should plan to visit their site at least once during the Thanksgiving Count and once during the New Year’s Count; although, visiting two or more times per monitoring period is highly recommended! Volunteers can monitor any number of sites so long as their resources, interest and capacity allow. In other words, the more monitoring the better.


How to Choose an Overwintering Site


Photo: Several monarch cluster trees within the San Leandro Marina Golf Course overwintering site, California, 2021-22. By Christina Garcia.

Work with your regional coordinator to choose which overwintering sites you will monitor for the upcoming Western Monarch Count (WMC). Sometimes, your regional coordinator may have special instructions for a site, so it’s always a good idea to run your monitoring plans by them first – even if you typically monitor the same site year after year.

Consider these 3 things when choosing your overwintering sites

  1. Identify priority sites with your regional coordinator. Occasionally, the Xerces Society will determine that certain sites meet a higher priority threshold and require additional monitoring attention during the overwintering season. If you have capacity to adopt an additional site, or aren’t attached to monitoring any one site in particular, please let your regional coordinator know so that they may ensure volunteer monitoring coverage of all priority sites.
  2. Think about timing and capacity. Monarch counts should occur early in the morning so that temperatures are cool and clusters remain intact from the evening before. Consider choosing a site near your home or a place you frequent often so that you can guarantee an early arrival. Or, if you prefer adopting sites in more rural locations, consider camping nearby and making an annual adventure out of it!
  3. Determine Site Access. Some overwintering sites require site access coordination and permissions before monitoring activities can occur. It is vital that WMC volunteers attain written permission from the relevant landowner or managing agency prior to entering a private site or site with limited access. The Xerces Society and WMC regional coordinators will do their best to coordinate and communicate site access details with volunteers, but ownership and access data may be limited. At times, volunteers may arrive at a site where access is denied, limited or unclear. In these situations, it is best to refer to the Code of Conduct and err on the side of caution; trespassing is never condoned.

Perks of Regular Monitoring


Although not a requirement, monitoring the same overwintering site each year can prove both fulfilling to you, the volunteer, and beneficial for the monarch butterflies. For example, developing deeper familiarity with an overwintering site may allow you or others to quickly identify site disturbances and/or potential threats to the overwintering monarchs and their habitat. You are encouraged to note any site disturbances or threats in your Monarch Count or Habitat Assessment datasheets and the Xerces Society may reach out to you for additional information or clarification. In this way, you are not only engaging in a fun community science project, but also serving as an advocate and conservationist for monarchs and their habitat. Additionally, you might notice that you’re monitoring more efficiently and effectively as you gain a better understanding of the nuances and trends within a site (e.g., when and where monarchs tend to cluster, what environmental resources they rely on, etc.). If you can commit to several years of monitoring, please let your regional coordinator know.