Why animals rely on seasonal cues—and why climate change can make them unreliable
Migrating animals time their journeys using a mix of external signals, such as temperature, wind, and pressure, and internal signals, such as day length and reproductive readiness. A useful framework describes migration as being pushed by external conditions (like deteriorating weather) and pulled by internal states (like photoperiod, the length of daylight) [1]. When climate change alters the timing or strength of those external signals, the cues can become less reliable—they may no longer point to the same conditions they once did.
In mallards, the balance between these cues shifts with the season: autumn migration is mainly pushed by declining temperatures, favorable winds, and falling barometric pressure, while spring migration is pulled more by photoperiod, which overrides weather as the primary driver [1]. This seasonal split matters because climate change may affect the reliability of weather cues differently in autumn and spring, potentially disrupting one season more than the other [1].
How timing shifts when cues change
When spring conditions become less predictable, animals that rely on weather cues may mistime their arrival. In Arctic breeding geese, the predictability of spring conditions along different migration routes influences the timing of migration, suggesting that cue reliability affects when birds move [2]. For some birds, earlier spring migration is associated with warmer temperatures and a higher North Atlantic Oscillation index, a large-scale climate pattern [5]. This link suggests that as temperatures warm, some species may migrate earlier, but the response may depend on the route and the cues used.
In mallards, weather still affects migration distances even in spring: warmer minimum temperatures in February increased distances by 62%, while strong north winds in March reduced movement by up to 213% [1]. These numbers show that even when photoperiod dominates, weather can still modulate how far birds travel, so changes in weather patterns could alter the pace of migration.
Routes may shift, but not all species respond the same way
Changes in cue reliability can also affect migration routes. For Arctic geese, different flyways experience different levels of spring predictability, and this may lead to route-specific timing adjustments [2]. In coastal sharks and large teleost fishes, temperature appears to determine the timing of immigration and the duration of residency, while photoperiod may cue immigration and emigration in adults when migrations are tied to predictable reproductive functions [3]. Rising temperatures due to climate change may therefore have variable effects on residency patterns over the course of an animal's development [3].
Not all species use the same cues, and some may be more flexible than others. In two tropical butterflies, humidity serves as a cue for seasonal wing pattern plasticity, but the two species integrate this cue in distinct ways: one responds directly to humidity, while the other responds indirectly through changes in host plant quality [4]. Although this example concerns wing patterns rather than migration, it illustrates that even closely related species can differ in how they use environmental cues, which may affect how they respond to climate-driven changes in cue reliability.
Sources used in this answer
Balancing opposing cues: seasonal shifts in push–pull drivers of migration in a temperate waterfowl species
In mallards, autumn migration is primarily driven by environmental push cues (temperature, wind, pressure), while spring migration is driven more by photoperiod, suggesting climate change may disrupt cue reliability differently across seasons.
Forecasting spring from afar? Timing of migration and predictability of phenology along different migration routes of an avian herbivore
The predictability of spring conditions along different migration routes influences the timing of migration in Arctic breeding geese.
Temporal community structure and seasonal climatic migration of coastal sharks and large teleost fishes in the northeast Gulf of Mexico
In coastal sharks and large teleost fishes, temperature may determine the timing of immigration and residency duration, while photoperiod may cue immigration and emigration in adults for predictable reproductive functions; rising temperatures may have variable effects on residency patterns over ontogeny.
Contrasting mechanisms for using humidity as cue for seasonal polyphenism in two tropical butterflies.
Two tropical butterfly species use humidity as a cue for wing pattern plasticity in distinct ways, with one responding directly and the other indirectly through host plant quality.
North Atlantic Oscillation and timing of spring migration in birds
Earlier spring migration in birds is associated with warmer temperatures and a higher North Atlantic Oscillation index, and the response may vary along different sections of migration routes.