Monarchs Reared in Winter in California Are Not Large Enough to Be Migrants. Comment on James et al. First Population Study on Winter Breeding Monarch Butterflies, Danaus plexippus (Lepidoptera: Nymphalidae) in the Urban South Bay of San Francisco, California. Insects 2021, 12, 946
Davis AK. Insects, January 2022.
Read the paper Free to read · doi:10.3390/insects13010063
What this paper is about
A published comment on the San Francisco winter breeding study, also in this list.
The argument is about body size: the author holds that monarchs reared through a Californian winter do not grow large enough to be migrants, so winter breeding is not a shift in overwintering strategy. Europe PMC holds only the opening line of the abstract.
Summarised here from the abstract below. Not the authors’ words.
Abstract
A recent study in this journal aimed to understand certain changes in the wintering behavior of monarch butterflies, specifically in the western subpopulation of North America [...].
Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.
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Milkweed USA. (2026). Monarchs Reared in Winter in California Are Not Large Enough to Be Migrants. Comment on James et al. First Population Study on Winter Breeding Monarch Butterflies, Danaus plexippus (Lepidoptera: Nymphalidae) in the Urban South Bay of San Francisco, California. Insects 2021, 12, 946 (listing). Retrieved DATE, from https://milkweedusa.com/research/monarchs-reared-in-winter-in-california-are-not-large-2022/
"Monarchs Reared in Winter in California Are Not Large Enough to Be Migrants. Comment on James et al. First Population Study on Winter Breeding Monarch Butterflies, Danaus plexippus (Lepidoptera: Nymphalidae) in the Urban South Bay of San Francisco, California. Insects 2021, 12, 946 (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/monarchs-reared-in-winter-in-california-are-not-large-2022/. Accessed DATE.
Milkweed USA. "Monarchs Reared in Winter in California Are Not Large Enough to Be Migrants. Comment on James et al. First Population Study on Winter Breeding Monarch Butterflies, Danaus plexippus (Lepidoptera: Nymphalidae) in the Urban South Bay of San Francisco, California. Insects 2021, 12, 946 (listing)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/research/monarchs-reared-in-winter-in-california-are-not-large-2022/.
@misc{milkweedusa_researchmonarchsrearedinwint,
title = {Monarchs Reared in Winter in California Are Not Large Enough to Be Migrants. Comment on James et al. First Population Study on Winter Breeding Monarch Butterflies, Danaus plexippus (Lepidoptera: Nymphalidae) in the Urban South Bay of San Francisco, California. Insects 2021, 12, 946 (listing)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/research/monarchs-reared-in-winter-in-california-are-not-large-2022/},
note = {Accessed DATE}
}