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1. Many migratory animals undergo physiological and behavioural changes to prepare for and sustain long‐distance movements. Because insect migrations are common and diverse, studies that examine how migratory insects meet the energetic demands of long‐distance movements are badly needed. 2. Monarch butterflies (Danaus plexippus) migrate up to 4000 km annually from eastern North America to wintering sites in central Mexico. Autumn generation monarchs undergo physiological and behavioural changes in response to environmental cues to initiate migration. In particular, exposure to cooler temperatures and shorter day lengths in early autumn causes monarchs to enter the hormonally induced state of reproductive diapause. 3. This study examined differences in flight‐associated metabolic rate (MR) and flight performance metrics for monarchs experimentally reared under autumn‐like conditions (typically experienced before the southward migration) relative to monarchs reared under summer‐like conditions. 4. Adult monarchs reared under autumn‐like conditions showed lower post‐flight MRs, greater flight efficiency, and lower measures of reproductive activity relative to monarchs reared under summer‐like conditions. Increases in post‐flight metabolism were associated with monarch body weight, age, and flight velocity. 5. These findings suggest that a trans‐generational shift in flight energetics is an important component of the monarch's complex migratory syndrome, and that physiological changes that accompany reproductive diapause facilitate energy conservation during flight.
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This content will become publicly available on January 1, 2026
Could bi‐axial orientation explain range expansion in a migratory songbird?
The likelihood of a new migratory route emerging is presumably a function of 1) the associated fitness payoff and 2) the probability that the route arises in the first place. It has been suggested that diametrically opposed ‘reverse' migratory trajectories might be surprisingly common and, if such routes were heritable, it follows that they could underlie the rapid evolution of divergent migratory trajectories. Here, we used Eurasian blackcap (Sylvia atricapilla; ‘blackcap') ringing recoveries and geolocator trajectories to investigate whether a recently evolved northwards autumn migratory route – and accompanying rapid northerly wintering range expansion – could be explained by the reversal of each individual's population‐specific traditional southwards migratory direction. We found that northwards autumn migrants were recovered closer to the sites specified by an axis reversal than would be expected by chance, consistent with the rapid evolution of new migratory routes via bi‐axial variation in orientation. We suggest that the surprisingly high probability of axis reversal might explain why birds expand their wintering ranges rapidly and divergently, and propose that understanding how migratory direction is encoded is crucial when characterising the genetic component underlying migration.
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- Award ID(s):
- 2143004
- PAR ID:
- 10573337
- Publisher / Repository:
- JAB
- Date Published:
- Journal Name:
- Journal of Avian Biology
- Volume:
- 2025
- Issue:
- 1
- ISSN:
- 0908-8857
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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