Scientific Findings
What do 18 years of tagging data reveal about fall migration?
Overview | Journal


The results of an 18-year tagging study were recently published by citizen scientist, Gayle Steffy, and provide remarkable insights about fall migration.

Based on the 11,333 monarchs she tagged in southern Pennsylvania, migratory success of monarchs east of the Appalachians is influenced by geography, year, timing, gender, and size.


Monarch Butterfly
Image by Betty Mattson

Monarch With Tag

1. Recovery rate: 1 in 200
Of the 11,333 monarchs tagged, 56 were recovered in Mexico, a recovery rate of 0.494%.

2. Early migrants more successful
More early (20 Aug–9 Sep) migrants than middle migrants (10 Sep–1 Oct) were recovered in Mexico. No late (2 Oct–20 Oct) migrants were recovered.

3. Wild more successful than captive-reared Captive-reared monarchs were significantly smaller and were much less likely to be recovered in Mexico. The recovery rate of only 0.065% (1 in 1,400 tagged) made captive-bred monarchs 7 times less successful.

Full Publication
Fall monarch butterfly migration: map showing two flyways

Steffy, Gayle. 2015. Trends Observed in Fall Migrant Monarch Butterflies (Lepidoptera: Nymphalidae) East of the Appalachian Mountains at an Inland Stopover in Southern Pennsylvania over an Eighteen Year Period. Ann. Entomol. Soc. Am. 1-11 (2015)

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