Long‐term monitoring indicates shifting fall migration timing in monarch butterflies (Danaus plexippus)

Abstract

The North American monarch butterfly (Danaus plexippus) is renowned for its annual multigenerational migration cycle. Every fall, individuals east of the Rocky Mountains travel up to 4300 km from their summer breeding range across the northern United States and southern Canada to central Mexico, where millions of butterflies aggregate at high densities in high-altitude oyamel fir (Abies religiosa) forests to overwinter (Calvert & Brower, 1986). However, declining populations observed in overwintering grounds have raised concerns for the conservation of this iconic species (Rendón-Salinas et al., 2020). Both diminishing habitat throughout the monarch's breeding range and increasing obstacles along their migratory journey have been implicated in this decline (Saunders et al., 2019;Taylor et al., 2020). Both of these conservation challenges may be further exacerbated by ongoing global climate change (Robinson et al., 2009;Wilcove & Wikelski, 2008).Previous research has indicated that climate change may threaten the migration and survival of monarchs in multiple ways, including changing microclimates in their overwintering habitat, increasing the strength and frequency of hurricanes on their migratory pathway along the Gulf of Mexico, and altering the range and toxicity of their

Opposing global change drivers counterbalance trends in breeding North American monarch butterflies

“…Meanwhile Ethier (2020) examined temporal trends in migrating monarch abundance for the southern Ontario region, and concluded there was no recent decline in the annual migratory cohort there, which is at the beginning of the migratory journey. Similarly, Culbertson et al (2021) found no evidence of declines over 30 years in the number of migrating monarchs in the Atlantic coast region. Our analysis considering NABA counts from the entire breeding population suggests that monarchs may have some ability to rebound from winter declines during the breeding season, perhaps providing some counteracting upward movement of monarch numbers despite declines in the winter.…”

“…Similarly, Culbertson et al (2021) found no evidence of declines over 30 years in the number of migrating monarchs in the Atlantic coast region. Our analysis considering NABA counts from the entire breeding population suggests that monarchs may have some ability to rebound from winter declines during the breeding season, perhaps providing some counteracting upward movement of monarch numbers despite declines in the winter.…”

The Effect of Global Warming on Migration of Butterflies

“…The fall migrations in the month of September and October are delayed by six days per decade, due to the high temperatures in these two months. This led to a decrease in the arrival of migratory numbers to winter sites in Mexico, which in turn affected the success of their migration and thus the destruction of these species (Culbertson et al, 2022). Studies indicated that the climate works in conflicting ways during the spring and summer.…”

Effects of climate on fall migration phenology of monarch butterflies departing the northeastern breeding grounds in Canada

“…Our analysis therefore explores various aspects of temperature and precipitation in the months leading up to fall migration to untangle their relative influence on several metrics of fall migration timing. Climate metrics used for phenological studies are frequently aggregated monthly to assess their effects on flight timing in butterflies (e.g., Culbertson et al, 2021;Zipf et al, 2017). We adopt this approach for comparative purposes (herein, the monthly climate average analysis).…”