Appendix 1: Sources and references for vulnerability assessment

1.1 Evidence for exposure (references)

1.1.1 Current impacts attributed to climate change:

No impacts recorded

1.1.2 Change in European range size between present day and 2100:

Using a species distribution model (SDM) we correlated species occurrence during the breeding season with a number of terrestrial and marine environmental variables. Species range data came from the European Breeding Bird Atlas (EBBA2) database. Present-day and 2100 terrestrial data were downloaded from the WorldClim database. We used data from the MRI-ESM2 general circulation model (GCM), which is a high-performing model over Europe. Present-day and 2100 marine data were downloaded from the Bio-Oracle database which averages predictions of marine variables from several different atmospheric-oceanic general circulation models (AOGCMS; for full details see Assis et al., 2017). For the map presented in the summary we used representative concentration pathway (RCP) 4.5, which is an “intermediate” emissions scenario. All data were at 5-minute resolution.

  • For Arctic Loon, Common Loon, Horned Grebe, and Red-necked Grebe we included the following terrestrial variables: Mean temperature of the warmest month, precipitation during breeding season, distance to sea
  • For Red-throated Loon we included the following terrestrial variables: Mean temperature of the warmest month, precipitation during breeding season, isolation of landmass, area of landmass, distance to sea
    No marine variables were included for this species group, as they are predominantly terrestrial during the breeding season.

Several other variables may strongly influence the distribution ofloons, divers and grebesand it is not possible to include all possible variables in a given model. However the following variables have previously been found to be important to predicting the distribution of loons, divers and grebes in Europe: distance to fresh water, freshwater depth, freshwater ph, freshwater chlorophyll concentration, land “roughness” index. For local assessments of climate change, we recommend these variables are strongly considered. We hope to incorporate these variables into future versions of this guidance document.

After running our model we generated a present-day map where every grid-cell is given a habitat suitability score between 0 and 1, where 1 is very suitable habitat and 0 is not at all suitable. We then compared this with a corresponding map built with 2100 data, and highlighted currently inhabitated areas where 1) suitability drops sharply (i.e. by more than 0.1) and 2) suitability drops below a probability threshold set by the model. Conversely we also highlighted areas where suitability rose sharply and above a given threshold. While a drop in habitat suitability is likely to result in population declines, it is not a certainty, and it does not mean that a population will be extinct in 2100 or that a population is doomed to extinction. With conservation action and careful management, along with changes in human behaviour, such declines may be mitigated or in some cases prevented. For a full explanation of the model see the accompanying ‘Methodology’ document.

Underlying data were downloaded from:
  • Keller, V., Herrando, S., Voríšek, P., Franch, M., Kipson, M., Milanesi, P., Martí, D., Anton, M., Klvanová, A., Kalyakin, M.V., Bauer, H.-G. & Foppen, R.P.B. (2020). European Breeding Bird Atlas 2: Distribution, Abundance and Change. European Bird Census Council & Lynx Edicions, Barcelona. Source of range data
  • Fick, S. E., & Hijmans, R. J. (2017). Worldclim 2: New 1-km spatial resolution climate surfaces for global land areas. International Journal of Climatology. http://worldclim.org/version2. Source of present-day and 2100 terrestrial data.
  • Assis, J., Tyberghein, L., Bosch, S., Verbruggen, H., Serrão, E. A., & De Clerck, O. (2018). Bio-ORACLE v2.0: Extending marine data layers for bioclimatic modelling. Global Ecology and Biogeography, 27(3), 277–284. https://doi.org/10.1111/geb.12693. Source of present-day and 2100 marine data

1.1.3 Changes in key prey species:

We first identified the key prey species for each species. This can be variable across a species range, but if available evidence suggested at least one major population is highly dependent on a particular prey species, then typically this species would be included. Lists of prey species were compiled from published sources, then verified and expanded following consultation with conservation practitioners. Afterwards we compiled current and projected maps of prey ranges to assess where key prey species may disappear in the near future. If any of the key species are predicted to vanish or drastically reduce in abundance in the current foraging range a given species, we marked this on the summary map.
We used several sources to collate range information, but for preference we used data from COPERNICUS as they include projected abundance. For species where this was not available we used habitat suitability instead. In all cases we used RCP 4.5, which is an “intermediate” emissions scenario. For species in the COPERNICUS database we used the 0.6 maximum sustainable yield parameter, which assumes international co-operation to work towards fish-stock sustainability. Our assessment is therefore relatively conservative in terms of changes in prey species.

Arctic Loon key prey species: herring (Clupea harengus), sprat (Sprattus sprattus) and cod (Gadus morhua). This species will also prey on freshwater fish, especially during the breeding season, notably salmoniids, minnows and sticklebacks. Freshwater species were not included in the key prey assessment. Prey species list was compiled from:
  • Jackson, Digger B. “Environmental correlates of lake occupancy and chick survival of black-throated divers Gavia arctica in Scotland.” Bird Study 52.3 (2005): 225-236.
  • Russell, R. W. (2020). Arctic Loon (Gavia arctica), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.arcloo.01
Common Loon key prey species: During the breeding season this species preys primarily on salmoniids. However, freshwater species are not assessed as part of the key prey assessment. Also feeds on a wide variety of marine species, however no key prey species were identified. Currently there is no key prey assessment for this species
Red-throated Loon key prey species: herring (Clupea harengus), sprat (Sprattus sprattus), sandeels (Ammodytes marinus), cod (Gadus morhua) and smelt (Osmerus eperlanus). This species also commonly preys on freshwater fish, especially during the breeding season, however these were not included in the key prey assessment. Prey species list was compiled from:
  • Rizzolo, D. J., C. E. Gray, J. A. Schmutz, J. F. Barr, C. Eberl, and J. W. McIntyre (2020). Red-throated Loon (Gavia stellata), version 2.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.retloo.02
  • Eriksson, Mats OG, and Heidi Paltto. “Vattenkemi och fiskbeståndens sammansättning i storlommens Gavia arctica häckningssjöar, samt en jämförelse med smålommens Gavia stellata fiskesjöar.” Ornis Svecica 20.1 (2010): 3-30.
Horned Grebe key prey species: three-spined sticklebacks (Gasterosteus aculeatus) and smelt (Osmerus eperlanus). This species also preys on small aquatic and airborne arthropods, particularly during the breeding season (beetles, dragonflies and damselflies, mayflies etc.). Invertebrates are not currently included in key prey assessments. While this species does prey on other fish species, none were identified as key species so were not included.. Prey species list was compiled from:
  • Stedman, S. J. (2020). Horned Grebe (Podiceps auritus), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.horgre.01
  • Piersma, Theunis. “Body size, nutrient reserves and diet of Red-necked and Slavonian Grebes Podiceps grisegena and P. auritus on Lake IJsselmeer, The Netherlands.” Bird Study 35.1 (1988): 13-24.
  • Dillon, Ian A., Mark H. Hancock, and Ron W. Summers. “Provisioning of Slavonian Grebe Podiceps auritus chicks at nests in Scotland.” Bird Study 57.4 (2010): 563-567.
  • Sonntag, Nicole, Stefan Garthe, and Sven Adler. “A freshwater species wintering in a brackish environment: Habitat selection and diet of Slavonian grebes in the southern Baltic Sea.” Estuarine, Coastal and Shelf Science 84.2 (2009): 186-194.
Red-necked Grebe key prey species: Smelt (Osmerus eperlanus), pilchard (Gasterosteus aculeatus), three-spined stickleback (Crangon crangon) and prawn (NA). This species feeds on various fish and invertebrates, including many freshwater species (dragonfly and caddis fly larvae among many others). Freshwater species were not included in the key prey assessment. Prey species list was compiled from:
  • Stout, B. E. and G. L. Nuechterlein (2020). Red-necked Grebe (Podiceps grisegena), version 1.0. In Birds of the World (S. M. Billerman, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.rengre.01
  • Piersma, Theunis. “Body size, nutrient reserves and diet of Red-necked and Slavonian Grebes Podiceps grisegena and P. auritus on Lake IJsselmeer, The Netherlands.” Bird Study 35.1 (1988): 13-24.
Prey range information for all species were compiled from:
  • COPERNICUS. (2021). Fish abundance and catch data for the Northwest European Shelf and Mediterranean Sea from 2006 to 2098 derived from climate projections. https://doi.org/10.24381/cds.39c97304
  • Kesner-Reyes, K., Kaschner, K., Kullander, S., Garilao, C., Barile, J., & Froese., R. (2019). AquaMaps: Predicted range maps for aquatic species. In R. Froese & D. Pauly (Eds.), FishBase. https://www.aquamaps.org

1.1.4 Climate change impacts outside of Europe

Common Loon
Several impacts of climate change have been noted in North American populations, including decreased brood size, changes in migration patterns, increased energetic stress due to higher temperatures, and an increase in exposure to mercury.
  • BirdLife
  • Bianchini, Kristin, et al. “Drivers of declines in Common Loon (Gavia immer) productivity in Ontario, Canada.” Science of the Total Environment 738 (2020): 139724.
Red-throated Loon
Climate warming in Arctic and sub-Arctic regions is reducing the area of suitable breeding habitat for red-throated loons. Warming increases lake depth in ice-bottomed lakes, increases the length of the ice-free season, and causes drainage of lakes, which are key loon breeding habitats. In their wintering range in California, mass mortalities have been caused by “red tides”, mass growth of red algae. It is difficult to attribute one event to climate change, but red tides have become more common and more widespread in California and globally, which has been linked to the effects of climate change.
  • BirdsoftheWorld
  • Jessup, David A., et al. “Mass stranding of marine birds caused by a surfactant-producing red tide.” PLoS One 4.2 (2009): e4550.

1.2 Sensitivity (references)

We used a list of candidate traits based on that in Foden & Young (2016) that indicate high sensitivity and identified which, if any, loons, divers and grebes possessed. In brief, we consulted published literature as well as expert knowledge and online databases such as Birdlife (http://datazone.birdlife.org/) and Birds of the World (https://birdsoftheworld.org), to assess whether loons, divers and grebes have either 1) Specialised habitat and/or microhabitat requirement 2) Environmental tolerances or thresholds (at any life stage) that are likely to be exceeded due to climate change 3) Dependence on environmental triggers that are likely to be disrupted by climate change, 4) Dependence on interspecific interactions that are likely to be disrupted by climate change or 5) High rarity.

For more detail and a full list of traits see:
  • Foden, W. B., & Young, B. E. (2016). IUCN SSC guidelines for assessing species’ vulnerability to climate change. Version 1.0 (Occasional paper of the IUCN Species Survival Commission No. 59)

1.3 Adaptive capacity (references)

We used a list of candidate traits based on that in Foden & Young (2016) that indicate adaptive capacity and identified which, if any, loons, divers and grebes possessed. In brief, we consulted published literature as well as expert knowledge and online databases such as Birdlife (http://datazone.birdlife.org/) and Birds of the World (https://birdsoftheworld.org), to assess whether loons, divers and grebes have either: 1) High phenotypic plasticity. 2) High dispersal ability or 3) High evolvability.

For more detail and a full list of traits see:
  • Foden, W. B., & Young, B. E. (2016). IUCN SSC guidelines for assessing species’ vulnerability to climate change. Version 1.0 (Occasional paper of the IUCN Species Survival Commission No. 59)