Working Group on Seabird Ecology (WGSE). ICES CM 2004/C:05 ...

4.2.2 Breeding success
It is a general finding in birds that early breeding is advantageous, so it is hardly surprising that several of the abovementioned
studies found that breeding success was related to the same climatic factors as phenology (Aebischer et al.,
1990; Ramos et al., 2002). Durant et al. (2003) found that breeding success in Atlantic puffins was related to SST in a
sigmoid fashion, while NAO had no effect. However, in tufted puffins there was a curvilinear relationship, with
breeding success being low at both the highest and lowest values of SST (Gjerdrum et al., 2003), and Diamond and
Devlin (2003) found no relationship between SST and breeding success. Despite low chick growth rates, horned puffin
breeding success in Alaska was high during year of ENSO-related low food availability (Harding et al., 2003). Inchausti
et al. (2003) found varying relationships between SST and breeding success for eight seabird species at the sub-
Antarctic Kerguelen and Crozet Islands: species foraging north of the Polar Front (wandering albatross, sooty albatross)
had high breeding success when SST was high, whereas those foraging south of the Polar Front (light-mantled sooty
albatross, blue petrel, thin-billed prion, white-headed petrel) showed the reverse relationship, and breeding success of
species foraging close to the islands (black-browed albatross, grey petrel) was independent of SST (Inchausti et al.,
2003). In southern fulmars, breeding success was low when sea ice concentration around the colony was low, as was
recruitment of new adults to the breeding population (Jenouvrier et al., 2003). In the closely related northern fulmar,
Thompson and Ollason (2001) found that breeding success was weakly negatively correlated with the NAO index,
indicating low breeding success following mild winters; they also found that the proportion of a birth cohort recruiting
to the breeding population depended on a global measure of summer temperatures in the northern hemisphere.
As an example of a direct effect, breeding success of Manx shearwaters on Rum was strongly affected by rainfall during
the breeding season, and was particularly low when heavy rainfall was frequent (Thompson and Furness, 1991).
4.2.3 Survival
Relating survival to climatic or oceanographic variables has proved to be considerably more challenging, or at least,
only few published studies to date have shown such correlations. In blue petrels in the southern Indian Ocean, winter
survival was strongly related to lagged variation in the Southern Oscillation Index, with survival being low during years
when SST was higher than normal (Barbraud and Weimerskirch, 2003). Climate interacted with population size so that
when a series of warm years occurred when population size was high, survival became very low and the population
crashed (Barbraud and Weimerskirch, 2003). In high-Antarctic southern fulmars, Jenouvrier et al. (2003) also found a
negative effect of winter SST on adult survival and attributed this to climatic effects on food availability. Jones et al.
(2002) found that survival of least auklets in the Pacific was related to an index of winter ocean climate throughout the
species’ range.
4.3 Scale issues
It seems reasonable to assume that the geographical scale at which seabirds are affected most directly by climate, and
thus where the strongest correlations are found, should be the one at which the birds interact with their environment.
Using climate variables measured at the “wrong” scale, or in the wrong place, is likely to lead to underestimation of the
strength of interactions between seabirds and climatic factors. Nevertheless, very few studies have explicitly considered
the issue of scale. Jones et al. (2002) found that adult survival of least auklets was correlated with climatic fluctuations
at the meso-scale, but not with a basin-wide index. Frederiksen et al. (in press) found that correlations between
phenology and climate in three North Sea seabirds depended on the species-specific non-breeding distribution. In two
dispersive species, common guillemot and black-legged kittiwake, phenology was related to the NAO index, whereas a
resident species, the European shag, bred earlier when local late-winter SST was high.
In this context, it is important to consider carefully which climate variables one tries to relate seabird performance to.
Using “standard” indices of large-scale processes, such as NAO and ENSO, may be tempting, because they are easily
available and seem to allow more general conclusions to be drawn. However, birds are more likely to react to conditions
at the time and place they actually encounter them, and the strongest correlations should therefore be expected at this
scale. Because climate variables at different scales are often intercorrelated, using the “wrong” variables may lead to
partially misleading conclusions about causal relationships. However, in pelagic seabirds, the areas used outside the
breeding season are often huge and not known in detail, and using large-scale indices is probably the best available
approach to correlating, e.g., overwinter survival of these species with climate.
4.4 Conclusions
The field of seabird-climate interactions is a very dynamic one, and this short review does not claim to provide a full
overview of all the published research; particularly, there is a bias towards very recent papers. However, it is clear that
an increasing number of researchers are both looking for and finding correlations between various aspects of seabird
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ICES WGSE Report 2004