Rafting for Science: Surveying Monarchs on the Green River

On September 11-13th, a team of National Park Service staff, volunteers, and myself as the LHIP Science Communications and Resource Monitoring intern surveyed the Green River for Monarch butterflies at all life stages. We floated from the Gates of Lodore (River Mille 243) to Split Mountain Boat Ramp ( River Mile 200). The survey was completed with 15 instars in various stages, 15 eggs, and no adult monarchs. Monarchs in any of these life stages were last found at river mile 240. The survey began at the end of a major storm that brought winds of 50+ mph, below freezing temperatures along with snow and rain. On the 11th the weather began to clear up and temperatures rose steadily with an average of 75° until the end of the trip. Milkweed was spotted consistently from Gates of Lodore Canyon to Split Mountain; it did become patchy in areas like Echo Park, Whirlpool Canyon, and Split Mountain. However, there were not many plants in bloom with sporadic and few nectar sources along the river. The predominant nectar sources were rabbitbrush, goldenrod, and purple species of Asters. Several of the Milkweed showed signs of predation and even stem cutting that’s associated with 5th instars. As well some empty chrysalis and empty eggs were found below river mile 240.

Gates of Lodore Canyon (river mile 242-227) This is where we had the most success on various beaches with strong showy milkweed patches. The upper part of the canyon above Winnie’s Rapid is where all instars and eggs were sighted.

Whirlpool Canyon (river miles 223-214) Little to no milkweed in the upper part of the canyon but the lower areas near Jones Hole had various sites with milkweed.

Island Park/Rainbow Park area (river miles 213-208) Had very few milkweed patches or desirable habitat for breeding. However, a good area for adults due to abundant nectar sources and roosting sites.

Split Mountain Canyon (river miles 207-201) Had few milkweed patches, mostly all in direct sun and tough. Not a lot of pollinator plants.

Comparing to last year’s Green River survey they were able to catch adults and observe Monarchs in all their life stages. However, they also noted the patchiness of milkweed along the riverbanks and had more success in capturing and tagging Monarchs. Likewise, the 2019 trip faced a similar bout of bad weather that included rains and lower temperatures. Additionally, since the 2019 trip departed at a similar date one can hypothesize that our low numbers, this year, are attributed to the severe storms that came through the area. That significantly and rapidly changed the climate conditions shocking the milkweed, nectar sources, and Monarchs themselves. If there is a 2021 survey, I hope it can be done in a similar time frame and with consistent weather (No storms), to serve as a control. That will either support the hypothesis or present new questions about how Monarchs move through Dinosaur National Monument.

To look back on the trip, a lot of questions come to mind. Did we not see any adults due to the weather? Were we too early or too late? Yet, it is hard to say what influenced the lack of sightings and why they stopped at Upper Lodore Canyon. It could be caused by the severe storm that rolled through the area and left a lot of the Milkweed flattened by the strength of the winds. Coupled with a sharp drop in temperature that decimated many of the pollinator plants and their flowers. Additionally, we will see another generation born on the river from the instars found that could make their way South and be tagged.

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