Science1 publisher2 min readPublished
Iowa State radio-tags 100 monarchs to test whether indoor rearing helps or hurts migration
Iowa State researchers released 100 Bluetooth-tagged monarch butterflies in September: 75 reared under three conditions and 25 caught in the wild. Tracking each route lets the team test whether indoor rearing helps or hurts the trip to Mexico.
The Scientist · Science desk
What happened
- Earlier tagging with small wing decals could show only whether a monarch reached Mexico, not the route it took to get there.
- The reared butterflies were raised entirely indoors, entirely outdoors, or indoors only during their final larval stages.
- The team will compare survival and whether each butterfly keeps the correct southwest heading during a migration of roughly eight weeks.
- The Iowa State study is one part of a larger project run with researchers at the University of Guelph in Ontario.
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Why it matters
- decision Conservation groups that encourage people to raise monarchs at home could get field evidence on whether indoor rearing costs a butterfly its survival or its sense of direction.
- capability Routes logged alongside weather would show where migrants stall or veer off course, information that a decal recovered in Mexico cannot record.
- constraint With an average of 25 butterflies per rearing condition in one season's release, only a large difference between methods is likely to stand out.
The wild-caught monarchs are the control. They make up a quarter of the 100 tagged butterflies [1]. They let the team measure each rearing method against animals that grew up without human help [6]. The article does not say how the 75 reared butterflies were divided among the three rearing groups [5].
The tracking is the new part. According to the article, the BluMorpho tags are the lightest tracking devices available [1]. They report near-real-time locations over Bluetooth to phones, tablets and computers in their area, and the article says they remove the battery-life problem [4]. Anyone with the Project Monarch app can switch on Bluetooth, search for tagged monarchs nearby and submit an observation [13].
So a position is logged only where a receiver happens to be. A monarch crossing open farmland with no listening device in range leaves the same gap in the record as one that has died [4]. Any survival comparison has to tell a dead butterfly from an unheard one [6]. I'd expect the routes to come back densest wherever people are carrying phones with Bluetooth on and the app running.
"The availability of small radio tags is a game changer," said John Pleasants, an emeritus adjunct associate professor in Iowa State's department of ecology, evolution and organismal biology [14][16]. He also said many of the monarchs that reach the overwintering forests in central Mexico originate in the Midwest [10]. "What we do here, as far as modifying landscapes to support monarch conservation, can have a big effect," he said [11].
The Iowa Monarch Conservation Consortium brings together more than 50 groups. Through it, more than 690,000 acres of monarch habitat have been established in Iowa since 2015 [12]. The eastern North American population has declined by as much as 80 percent [9].
Checking migrants' routes against that habitat would take a different analysis from the one this season's study describes. Katherine Kral-O'Brien, who oversees the consortium with Mykayla Hagaman [15], described the question the study was built to answer. "There's been a lot of debate around the best ways to help monarchs thrive. Should you bring them inside and rear them? And does that help or hurt them?" she said [7].
What to watch
- How many of the 100 tags are actually detected along the route and near the central Mexican forests, since that count sets the real sample for any survival comparison.
- The split of the 75 reared monarchs among the three conditions, and whether any group differs from the 25 wild-caught controls on survival or heading.
- Whether the University of Guelph project pools tagged monarchs from several release sites, which would enlarge each rearing group beyond one Iowa campus.