Please note: This discussion topic is one of a set about species that are endemic or nearly endemic to the European Union (EU), and whose status in the EU therefore effectively determines their global status. To ensure consistency between the 2020 global and EU Red List assessments of these species, this set of topics is being fast-tracked through BirdLife’s Globally Threatened Bird Forums to inform decisions on the EU (and global) status of relevant species, which must be finalised and communicated to the European Commission by mid-April 2020. Topics on other species will be posted on the Forums shortly, for discussion later in the spring, as per usual. The results of the 2020 global Red List update for birds will be published by IUCN and BirdLife in early December.
Audouin’s Gull Larus audouinii breeds on Mediterranean coasts, with its main breeding areas at the Ebro Delta (NE Spain) and Chafarinas Islands (off NE Morocco), and scattered colonies from Portugal, Morocco and Algeria east to the Aegean Sea, S Turkey and Cyprus; it winters south to Senegambia (Burger et al. 2020). It is currently listed as Least Concern, having been reclassified from Near Threatened in 2015, when its population was considered to be fluctuating (following a huge increase and range expansion) but not declining.
Globally, it has an extremely large extent of occurrence in both the breeding season (>2.2 million km2) and in winter (>8 million km2), and hence does not approach the thresholds for Vulnerable under the range size criteria (B and D2). Its population size is also moderately large, with 43,000–44,000 mature individuals in Europe alone (BirdLife International 2015), and hence does not approach the thresholds for Vulnerable under the population size criteria (C and D1). Therefore, the only potentially relevant criterion is A, which relates to reductions in population size. Until recently, however, its population was not thought to be declining at all, let alone sufficiently rapidly to approach the threshold for listing as Vulnerable under Criterion A (>30% decline over 10 years or three generations, whichever is longer). Consequently, it was evaluated as Least Concern.
In late 2019, all 28 EU Member States were obliged to complete their second 6-yearly report to the European Commission (EC) under Article 12 of the EU Birds Directive, including their latest information on the sizes and trends of the populations and ranges of all naturally occurring wild bird species. Under an EC contract to evaluate the EU population status of each species, BirdLife has now analysed these new data, which indicate that this species’s population has declined significantly in recent years. Specifically, the data reported by Spain (which holds >80% of the European and global population; BirdLife International 2015) suggest that the breeding population declined by 31% in just four years, from 2013 to 2017. No trend was reported by Portugal (11%), and Italy (7%) reported recent stability, but the small populations in France and Greece were also reported as declining.
Further information provided by SEO/BirdLife (J.M. Arcos in litt. 2020) confirms that the Spanish breeding population has in fact been declining since around 2010 (before which time, it fluctuated for several years, as reflected in the current global assessment). The latest version of the Spanish Government’s Marine Strategy for the Levantine coast and Balearic islands (Fig. 11, p. 44) shows that the breeding population peaked at 18,268 pairs in 2006, but had fallen to 10,231 pairs by 2017 (and has declined further since then; J.M. Arcos in litt. 2020). The equivalent Marine Strategy for the Alboran Sea (not currently available online) shows that the breeding population (which includes colonies in Spanish territory on the N African coast, such as Alhucemas, Ceuta and Melilla) also peaked in the mid-1990s at 4,384 breeding pairs, but had fallen to c. 1,900 pairs in 2017 (and has declined further since then; J.M. Arcos in litt. 2020). In total, the Spanish breeding population has declined from 21,264 pairs in 2006 to 12,131 pairs in 2017, and is still declining.
The number of birds breeding at the former main colony (Punta de la Banya) in the Ebro Delta has crashed, from 15,396 pairs in 2006 to 1,355 pairs in 2019 (Genovart et al. 2018; J.M. Arcos in litt. 2020). Some of these birds have relocated and established other colonies elsewhere within the Ebro Delta, including one of 746 pairs, as well as several smaller colonies that together hold up to 4,000 pairs (Oro et al. 2009). However, these recently formed colonies are often in suboptimal areas, such as ports. The main reason for these changes seems to be the presence of predators (e.g. fox, badger) in the Ebro Delta (Payo-Payo et al. 2018), and the lack of suitable nesting places elsewhere, aside from some artificial sites (e.g. ports, saltpans). Fishing moratoria and the reduction of fishing discards off the Ebro Delta may also be an important factor (Cama et al. 2013), although fisheries bycatch is still considered to be a significant threat to the species (Genovart et al. 2017).
The relocation of colonies may be expected in such a nomadic species, and some Spanish breeders are known to have moved to S Portugal (Calado et al. 2018), where numbers peaked at 2,934 pairs in 2018 (2,663 pairs in 2019; J.M. Arcos in litt. 2020). However, this redistribution does not compensate for declines elsewhere, and thousands of birds remain unaccounted for. At a recent meeting of the Spanish Working Group on Audouin’s Gull, attended also by Portuguese and N African experts, the possibility that some of these ‘missing’ birds may have moved to an unknown location(s) in N Africa was discussed (J.M. Arcos in litt. 2020). Morocco was thought unlikely; it was less clear for Algeria.
Notwithstanding this possible redistribution, combining the data currently available from Spain and Portugal (>90% of the global population) suggests an overall decline of around 30% since 2006. The relevant period for assessing trends in this species under Red List Criterion A is 24.3 years (based on an estimated generation length of 8.1 years; Bird et al. 2020). The current population level is about 15% lower than in the mid-1990s, so it does not approach the 30% threshold for listing as Vulnerable under A2 (past declines). However, including data from other countries, and extrapolating the trend observed since 2006 forward three generations (to 2030), implies an overall decline approaching 40%, which falls within the range for qualifying as Vulnerable under A4 (past, present and future declines). Projecting three generations farther into the future under A3 does not seem justified at present, until it is clearer whether the missing birds have relocated somewhere else, and whether the decline at least partly represents a readjustment to a lower and more natural carrying capacity, now that fishery discards have been reduced from the unsustainable levels of the early 2000s (Cama et al. 2013; Genovart et al. 2017).
Overall, this species’s global population appears to be declining at a rate approaching 40% over three generations (24 years), thereby qualifying it for reclassification from Least Concern to Vulnerable under Criterion A4b.
Relevant comments and information on this fast-track topic are welcome by 8 April 2020, please.
Please note that this forum topic is not designed to be a general discussion about the ecology of the species, but rather a discussion of the species’s Red List status. Therefore, please ensure your comments are relevant to the species’s Red List status and the information requested. By submitting a comment, you confirm that you agree to the BirdLife Forums’ Comment Policy.
Bird, J.P., Martin, R., Akçakaya, H.R., Gilroy, J., Burfield, I.J., Garnett, S., Symes, A., Taylor, J., Şekercioğlu, Ç.H. & Butchart, S.H. (2020). Generation lengths of the world’s birds and their implications for extinction risk. Conservation Biology. https://doi.org/10.1111/cobi.13486
BirdLife International (2015) European Red List of Birds: Audouin’s Gull Larus audouinii.http://datazone.birdlife.org/userfiles/file/Species/erlob/summarypdfs/22694313_larus_audouinii.pdf
Burger, J., Gochfeld, M., Garcia, E.F.J. & Sharpe, C.J. (2020). Audouin’s Gull (Larus audouinii). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. https://www.hbw.com/species/audouins-gull-larus-audouinii
Calado, J.G., Matos, D.M., Ramos, J.A., Moniz, F., Ceia, F.R., Granadeiro, J.P. and Paiva, V.H., (2018) Seasonal and annual differences in the foraging ecology of two gull species breeding in sympatry and their use of fishery discards. Journal of Avian Biology, 49(1).
Cama, A., Bort, J., Christel, I., Vieites, D.R. and Ferrer, X. (2013) Fishery management has a strong effect on the distribution of Audouin’s Gull. Marine Ecology Progress Series 484: 279-286.
Genovart, M., Doak, D.F., Igual, J.M., Sponza, S., Kralj, J. and Oro, D. (2017) Varying demographic impacts of different fisheries on three Mediterranean seabird species. Global Change Biology 23: 3012-3029.
Genovart, M., Oro, D. and Tenan, S. (2018) Immature survival, fertility and density dependence drive global population dynamics in a long‐lived species. Ecology 99: 2823-2832.
Oro, D., Pérez-Rodríguez, A., Martínez-Vilalta, A., Bertolero, A., Vidal, F. and Genovart, M. (2009) Interference competition in a threatened seabird community: a paradox for a successful conservation. Biological Conservation 142: 1830-1835.
Payo-Payo, A., Sanz-Aguilar, A., Genovart, M., Bertolero, A., Piccardo, J., Camps, D., Ruiz-Olmo, J. and Oro, D. (2018) Predator arrival elicits differential dispersal, change in age structure and reproductive performance in a prey population. Scientific Reports 8: 1-7.