Large study of the breeding phenology of seabirds across the North Atlantic

Successful breeding is crucial, but climate change can make timing of breeding more demanding. A new study including data from several colonies monitored throughout the SEAPOP programme has now examined how seabirds adjust their breeding phenology.

The importance of timing

Timing of breeding, an important driver of fitness in many populations, is widely studied in the context of global change, yet despite considerable efforts to identify environmental drivers of seabird nesting phenology, for most populations we lack evidence of strong drivers. In a study of multiple species, researchers adopted an alternative approach, examining the degree to which different populations positively covary in their annual phenology to infer whether phenological responses to environmental drivers are likely to be (a) shared across species at a range of spatial scales, (b) shared across populations of a species or (c) idiosyncratic to populations (no positive covariance between populations in the same region or of the same species).

Laying dates locally correlated

Combining 51 datasets on breeding phenology spanning 50 years from nine seabird species across 29 North Atlantic sites, the researchers examined the extent to which different populations share early versus late breeding seasons depending on a hierarchy of spatial scales. In about a third of the cases, it was found that laying dates of populations of different species sharing the same breeding site or small-scale breeding region were positively correlated, which is consistent with the hypothesis that the seabirds share phenological responses to the same environmental conditions. In comparison, they found no evidence for positive phenological covariation among populations across species aggregated at larger spatial scales.

Kittiwakes stand out

In general, the study gave little evidence for positive phenological covariation between populations of a single species, and in many instances the inter-year variation specific to a population was substantial, consistent with each population responding idiosyncratically to local environmental conditions. The black-legged kittiwake (Rissa tridactyla) was the exception, with populations exhibiting positive covariation in laying dates that decayed with the distance between breeding sites, suggesting that populations may be responding to a similar driver.

Improves our understanding of seabird phenology

The study sheds light on the potential factors that may drive phenology in the studied species, thus furthering our understanding of the scales at which different seabirds interact with interannual variation in their environment. The researchers also identified additional systems and phenological questions to which their inferential approach could be applied.

Read the article:

• Variation and correlation in the timing of breeding of North Atlantic seabirds across multiple scales