Why Tired Gulls Abandon Their Colony Sooner
Recent fieldwork on three‑year‑old gulls nesting on Alaska's Middleton Island has revealed a striking pattern: individuals that expend excessive energy during a demanding breeding season tend to depart their breeding grounds earlier than their peers. This premature exodus is not merely a reaction to a failed clutch; it appears to be a strategic response to the physiological toll of raising chicks under harsh conditions.
Experimental design and energy manipulation
The international team tracked 251 gulls from 2021 to 2024, dividing them into three experimental groups. The first cohort received supplemental feed, which reduced the energetic burden of chick rearing. The second group suffered a temporary handicap: researchers trimmed three primary wing feathers and two tail feathers shortly after egg‑laying, making flight more labor‑intensive for the remainder of the breeding period. The third cohort served as a control, experiencing no intervention.
Outcomes were stark. Only 10 % of the handicapped birds successfully fledged a chick capable of independent flight, compared with 44 % in the fed group and 43 % in the control group. Moreover, the feather‑trimmed gulls left the colony roughly ten days ahead of schedule, confirming that heightened energy demands accelerate departure.
Longer journeys and mixed fortunes
Each bird carried a lightweight geolocator, allowing researchers to reconstruct post‑departure movements. Those that left early embarked on considerably longer migrations than their counterparts. The extended trek seems to provide a recovery window, boosting the probability of a successful breeding attempt the following year. However, this advantage comes at a cost: only 67 % of the early‑departing individuals returned to the colony the next season, versus 90 % of the well‑fed group and 83 % of the control group.
Energetic flexibility as a survival strategy
The authors describe the observed behavior as “energetic flexibility”—the capacity of an animal to reallocate limited energy reserves among reproduction, migration distance, and survival odds. By opting for a longer, more demanding migration, exhausted gulls may improve future reproductive success, yet they simultaneously increase their risk of mortality during the arduous journey.
Implications for a changing climate
Understanding this trade‑off is increasingly vital as climate change reshapes oceanic productivity and weather predictability. Shifts in prey availability and more erratic storm patterns could force seabirds to adjust the timing and intensity of their breeding efforts, potentially amplifying the need for flexible energy budgeting.
These findings, published in the Proceedings of the Royal Society B, underscore how events in one season can cascade into the next, influencing both the reproductive output and the long‑term viability of seabird populations.
Source: https://scientias.nl/waarom-uitgeputte-meeuwen-eerder-vertrekken-en-verder-vliegen/
