Marine Birds Thematic Assessment

Climate change effects on marine birds

A changing climate acts as a pressure on the marine ecosystem (including the OSPAR Maritime Area) and the human activities within it. It leads to rising sea level and temperatures, changes in the amount of rainfall and reduced sea-ice coverage, among other effects. These pressures have resulted in documented changes in marine ecosystems, see: Climate Change Thematic Assessment . 

The section below summarises the main impacts of climate change on marine birds. Information is provided separately for seabirds and waterbirds, as these two groups are likely to be differentially affected by climate change due to their different ecological characteristics.

Seabirds

• Dias et al., (2019) in a major global review of threats to seabirds, identified climate change in the top three most important threats. In the OSPAR region specifically, climate change is identified as important driver of change, for example in the United Kingdom (e.g. Pearce-Higgins et al., 2021; McDonald et al., 2015; Mitchell et al., 2020) and also in the Baltic (e.g. Meier et al., 2022).
• Hakkinen et al., (2022) summarised the main mechanisms for climate-change impacts on seabirds in western Europe and ranked their importance according to questionnaire responses gathered from seabird conservation practitioners (Table CC.1).

Table CC.1: Climate change impacts on seabirds according to conservation practitioners. Taken from Hakkinen et al., 2022)

• The main mechanism for climate-change impacts on seabirds is change to their food supply and / or availability, though there is growing evidence that severe weather events also play an important role, for example in nest survival, but also in the survival of adults trying to forage during storms during the non-breeding season (Clairbaux et al., 2021, Reiertsen et al., 2021).
• Some of the best evidence of climate-induced changes to demographic rates (adult survival, breeding success) of seabirds comes from the black-legged kittiwake, a surface-feeder. Studies show that its over-winter survival is lower following winters with increased sea-surface temperatures (SST), with reduced breeding success one year later (Frederiksen et al., 2004, 2005, 2007; Frederiksen, 2014). These patterns are likely to be mediated by the abundance of one of the kittiwake’s preferred prey, namely energy-rich sandeels Ammodytes spp. (Daunt et al., 2008; Eerkes-Medrano et al., 2017). The recruitment of sandeels is in turn influenced by climate-induced changes in plankton abundance, distribution and timing (Wanless et al., 2018). There have been northward shifts in the distribution of sandeels’ key copepod prey, caused by climate change (Reygondeau and Beaugrand, 2011). As discussed in the ( Pelagic Habitats Thematic Assessment , the indicator results for QSR 2023 reveal that increasing sea surface temperatures are linked to declining abundances of planktonic lifeforms, particularly small and large copepods, across the North-East Atlantic.
• More recent evidence suggests that other seabird species’ food supply is also affected by climate-change impacts; the proportion of sandeels in the diet of seabirds in a colony in South East Scotland has declined over the last three decades, linked to changes in Sea Surface Temperature (SST) (Howells et al., 2018; Wanless et al., 2018; Harris et al., 2022).
• In the context of climate change, there is also a need to account for natural variability over multi-decadal time scales in the marine environment of the North Atlantic, as demonstrated by the importance of SST for puffin productivity in SW Iceland over a 130-year period (Hansen et al., 2021).
• While most research has focused on SST-mediated changes, recent evidence has emerged of other mechanisms, including the effects of climate-mediated water-column stratification on kittiwake breeding success (Carroll et al., 2015).
• As well as climate-mediated changes in the abundance of seabird prey, there have also been mismatches between the timing of the occurrence of seabird prey and periods of peak energy demand (e.g. chick-rearing) (Burthe et al., 2012).

Waterbirds

• Climate change may affect waterbird populations while they are in their northern / Arctic breeding grounds, on their migration stopovers and in their wintering grounds. Waterbirds that breed in temperate parts of the OSPAR Maritime Area may also be subject to climate-change impacts, particularly so for upland and more northern species.
• Climate change may impact abundance, distribution and the timing of occurrence, particularly in migration and in wintering areas (Pavón-Jordán et al., 2019).
• Shifts in distribution, mediated by temperature changes, have been seen within the OSPAR Maritime Area and more generally within Europe, with waders and wildfowl species during the winter increasingly concentrated in north-eastern areas with, for example, fewer reaching south-western parts of their former range (so-called “short-stopping”).
• Warmer winter temperatures have been linked to the earlier departure of waterbirds for their northern breeding grounds.
• Projected rises in mean sea-level as a result of climate change are expected to impact the extent and quality of waterbird habitats.

What has changed since the last Quality Status Report

The Quality Status Report 2010 identified climate-change impacts as an increasing pressure on marine ecosystems. In relation to seabirds, the QSR 2010 made the following projection for climate-change impacts: 

"Impacts on seabirds are likely to be more important through changes in their food supply than through losses of nests due to changed weather"

The section below provides some considerations relating to the QSR 2010 projections based on the current status of marine birds in the OSPAR Maritime Area.

Did the foreseen change happen? 

It is more likely than not that the change foreseen above did happen, though there is increasing evidence that loss of nests due to extreme weather might be playing an increasingly important part. 

It is not possible to distinguish with any certainty between these two scenarios by reference to changes in the integrated assessment results or the individual indicators between QSR 2010 and QSR 2023, because both scenarios would to some degree impact both indicators, i.e., breeding abundance (B1) and breeding productivity (B3), albeit probably over different time-scales. For example, changes in food supply and accessibility might impact adult survival and therefore B1, but also impact food supply to chicks (B3). Similarly, reductions in nest survival impact directly on B3 but also, with increasing effect in later years, on B1 (fewer chicks are recruited into the breeding population). It should also be noted that marine birds have proved unable to adjust their timing of breeding optimally in response to changing climate conditions (Keogan et al., 2017). Also, effects are often species-specific and region-specific, which contributes to the difficulties in attributing coarse-scale changes in the indicators (whether integrated or not) to climate-change effects demonstrated in the literature.

Nevertheless, the State section indicates that there was no significant change in the status of species groups between 2010 and 2020 (applying the same method retrospectively to both periods); in other words, the status of all species groups (apart from grazing feeders) was not good in 2010 and was still not good in 2020, although the state of individual species may have deteriorated since the last assessment. However, even if there had been a change between these two assessments, the degree to which it might have been attributable to climate change impacts would, of course, not be known.

It should be noted that there are likely to be biases in terms of the location of evidence for climate-change effects in seabirds, particularly towards studies in the central North Sea (and in particular around the Isle of May in SE Scotland, where sandeels are the dominant prey). As the OSPAR Maritime Area is large and diverse, we recommend further examination of regional effects, a comprehensive assessment of which is beyond the scope of this section (but for example, some effects for kittiwakes are less strong in Celtic Seas (Lauria et al., 2013; Cook et al., 2014)).

A recent survey of seabird conservation practitioners in the OSPAR Maritime Area (Hakkinen et al., 2022) showed that 79% saw changes in food supply as a serious or very serious threat to the seabird populations they managed, while 45% thought that nest destruction posed the same threat.

Johnston et al., (2021), in a review of climate-change impacts on seabirds in the Celtic Sea, concluded that the strongest evidence of long term impacts of climate change in seabirds comes from studies in which impacts are mediated through changes in prey associated with changes in sea surface temperature. This has been demonstrated in systems where the predominant prey is sandeels. (Frederiksen et al., 2005), herring (Durant et al., 2003) or sprat (Österblom et al., 2006), in studies of surface-feeding and pelagic-feeding seabirds. Johnston et al., (2021) further conclude that there is also evidence for impacts of short-term extreme weather events (e.g., on nest survival) but that to date this has been less impactful on seabird population size than climate-mediated prey availability. However, they also identify that if such events become more frequent – as has been proposed in many climatic forecasts – then such impacts may become more important. 

Mitchell et al., (2020) concluded that, while the principal mechanism for climate-induced declines in seabird abundance in the United Kingdom is reductions in food supply, there is growing evidence that short term, extreme, weather events have an important effect.

How has the change happened?

There is some evidence that the observed rate of change in the abundance of “true seabirds” since 2010 has not been as negative or severe as was predicted by models that forecast changes up to 2050. However, this tendency is probably not very apparent in the Norwegian part of OSPAR Region I, which holds >50% of European ocean areas. For instance, the number of seabird species on Norway’s Red List has increased constantly from 26% in 1998, 48% in 2010 to 63% in 2021 (34 of 54 species), almost exclusively assessed from population trends over three generations. For kittiwakes, one of the listed species, some iconic colonies have gone extinct during the last five years, much sooner than the predictions made by Sandvik et al., (2014). N.B. this does not directly address the specific question regarding relative importance of food supply and extreme events.

Pearce-Higgins et al., (2021) provided the first assessment of the projected (from 2010 to 2050) impact of expected climate change on seabird populations (i.e. “true seabirds”) in the North-East Atlantic. 15 of the 19 species modelled were predicted to decline in Britain and Ireland; the most impacted species was the Arctic skua, which the authors predict will cease to breed there by 2050 (though the mechanism for this is likely to be direct physiological intolerance to heat rather than prey effects or nest loss due to extreme weather events). Steep declines of greater than 50% of abundance were predicted for fulmar, puffin, Arctic tern, little tern, Sandwich tern and storm-petrel, although the latter three species have results which are less reliable. Indeed, for all these species (except the Arctic skua) a scenario of no change in abundance falls within the spread of credible scenarios. Furthermore, for common gull, lesser black-backed gull, razorbill and puffin, the observed short term changes in abundance were more positive than the model had predicted. It should be noted that Pearce-Higgins et al., (2021) were not able to include in their study specific parameters for sea-level rise or increased storminess, which were identified by Johnston et al., (2021) as potentially important mechanisms for climate-mediated impacts on seabirds. Therefore, it is not possible to use the study of Johnston et al., to directly compare the modelled food-supply effects and those of nest loss due to extreme weather events.

What has been the impact? [strong negative / mild positive etc]

The state section indicates that there was no significant change in the status of species groups between 2010 and 2020 (applying the same method retrospectively to both periods); in other words, the status of all species groups (apart from grazing feeders) was not good already by 2010 and was still not good in 2020. It is of note that climate-change effects on seabirds had been detected before 2010 (e.g., Frederiksen et al., 2005), and it may be assumed that they contributed to the suppression of seabird demographics. There are some more subtle changes, however: the trend in the proportion of species in good status between 2010 and 2020 shows a slight improvement in surface feeders in Arctic waters, a decline in water-column feeders in Arctic waters, a decline in benthic feeders in the Greater North Sea and a decline in wading feeders in Celtic Seas. Furthermore, examination of the status of wading feeders by species reveals evidence of a greater number of species (six) showing good status for abundance (B1) in Greater North Sea and not good status in Celtic Seas, compared with only two species with good status for abundance in Celtic Seas and not good status in Greater North Sea. While this is consistent with the studies demonstrating north-easterly shift in distribution of this group of birds (Austin and Rehfisch, 2005; Maclean et al., 2008) the degree to which the patterns shown by the QSR indicators are attributable to climate change impacts is not known.