Seabirds time egg-laying to ocean plankton blooms, not just calendar dates
Siddiqi-Davies K, Gillies N, Bailey H, Bond S, Fayet A
Phenology
The timing shifts documented here hinge on phytoplankton blooms, the same microscopic ocean plants that gardeners rarely think about but that anchor the entire food web feeding the birds many of us watch along the coast.
Researchers followed a seabird colony for 16 years and found that laying eggs earlier used to mean more chicks survived, but that's less true now. The birds actually adjust their egg-laying timing based on when tiny ocean plants called phytoplankton bloom each spring, with stronger blooms pushing birds to breed earlier. It's a reminder that even for animals, plant life at the bottom of the food chain quietly sets the pace for everything above it.
Key Findings
Earlier laying no longer consistently predicts higher breeding success; later laying has become less costly in recent years
Birds adjusted lay date based on interannual variation in Celtic Sea phytoplankton bloom timing, with stronger blooms linked to stronger selection for early breeding
No long-term advancement in spring bloom onset was detected over the 16-year study, despite a slight advancement in breeding pairs' lay dates
chevron_right Technical Summary
Scientists tracking Manx shearwaters for 16 years found that laying eggs earlier doesn't always mean better breeding success anymore, and birds time their egg-laying partly around when ocean plankton blooms happen each year.
Abstract Preview
Original paper
Why don't all birds lay early? Causes and consequences of breeding timing for a long-lived migratory seabird.
The relationship between earlier laying and higher breeding success is well-established in avian species. However, a wide distribution of breeding timings is often maintained within a population, a...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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Phytoplankton are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from Ancient Greek φυτόν (phutón), meaning "plant", and πλαγκτός (planktós), meaning "drifter, wanderer, roamer", and thus, "plant drifter".