Balearic Shearwater Puffinus mauretanicus


Justification of Red List category
This species has a small breeding range and a relatively small population which is undergoing an extremely rapid decline, largely related to low adult (and immature) survival rates. Main threats are fisheries by-catch at sea and predation at breeding colonies by introduced mammals. Population models predict over 90% decline in three generations with an average extinction time of about 60 years, hence qualifying the species as Critically Endangered.

Population justification
Estimates for the breeding population size in the last two decades ranged from about 2,000 to 4,500 pairs (Ruiz and Martí 2004, Arcos et al. 2011), with the current official figure being 3,142 pairs (ACAP 2012). This includes: Mallorca 900, Menorca 405, Cabrera 475, Ibiza 650, Formentera 712. However, these figures should only be taken as indicative, as breeding sites are often inaccessible, and therefore their census relies on indirect methods (e.g. counts of rafts, vocalisations, etc.) that are subject to strong biases and inaccuracy. This calls for particular caution in inferring population trends from such data, as estimates from one year to another might simply vary because of changes in methodological assumptions, people involved, environmental conditions during counts, or simply subjective perceptions. In fact, recent research at sea using two approaches (boat-based surveys and coastal counts at the Gibraltar Strait migration bottleneck) point to a global population of about 25,000 individuals, suggesting that the breeding population could be larger than previously assumed (Arcos et al. 2012b, Arroyo et al. 2014). Starting from these global figures, and assuming that the population structure was at equilibrium, Genovart et al. (2016) inferred a breeding population size of about 7,200 pairs, although this optimistic figure should also be taken with caution.

Trend justification
Using a population estimate of 2,000-2,400 breeding pairs, Oro et al. (2004) estimated a mean decline of 7.4% per year and a mean extinction time, as estimated by population viability analysis, of just over 40 years. This equates to an ongoing population decline of more than 80% in three generations (54 years). A new modelling assessment was conducted recently, using new demographic data and improved capture-recapture modelling procedures (Genovart et al. 2016). Furthermore, the new modelling used as a departure point a global population estimate of 23,780 birds, consistent with the recent estimates at sea (Arroyo et al. 2014). Despite these improvements in both the analysis and the background information, the trend was still severely declining, with a population decline of 14% per year, and an average extinction time of 61 years if the current trend is maintained over time. Note that this analysis was conducted assuming a population at equilibrium, estimated at 7,200 breeding pairs, which still needs to be confirmed on the ground. If the breeding population is found to be lower, the time to extinction would be shorter. Moreover, the analyses were based on data from an important colony free of predators, meaning that the average survival rate of whole population could be even lower.

Distribution and population

The species breeds exclusively in the Balearic Islands, Spain, occupying the five major island groups: Menorca, Mallorca, Cabrera, Ibiza and Formentera. During the breeding period (late February - early July) the main foraging areas are located along the Mediterranean shelf of the Iberian Peninsula, mainly around the central Catalan coast, the Ebro Delta-Columbretes area and the Cape Nao (Arcos and Oro 2002, Louzao et al. 2006a, Arcos et al. 2012a, Meier et al. 2015), with individuals potentially exploiting the closest productive areas to their breeding colonies (Louzao et al. 2011a). Some birds also exploit foraging grounds at the extreme of their distribution in the continental shelf off Algeria and Morocco as well as in the Gulf of Lion (Ruiz and Martí 2004, Louzao et al. 2012, Meier et al. 2015, Afán 2016), in addition to the waters around the Balearic archipelago (Ruiz and Martí 2004, Louzao et al. 2011b). The bulk of the population leaves the Mediterranean after breeding, and concentrates off the Atlantic coasts of SW Europe in summer-autumn, mainly in Spain, Portugal and France, and also southwestern UK and northwestern Morocco (Le Mao and Yésou 1993, Ruiz and Martí 2004, Ramírez et al. 2008, Arcos et al. 2009, Guilford et al. 2012, Pérez-Roda 2015). Birds return to the western Mediterranean in autumn (mainly October), and spend the winter months roughly in the same foraging areas used during the breeding period (Le Mao and Yésou 1993, Ruiz and Martí 2004, Guilford et al. 2012).

At one population, on Menorca, which shows evidence of past hybridisation with the closely related Yelkouan shearwater (Puffinus yelkouan), migratory behaviour and breeding phenologies appear to be intermediate with Yelkouan’s, with a majority of birds apparently remaining in the western Mediterranean post-breeding (Meier 2015). 


The Balearic Shearwater breeds in caves, burrows and crevices on islets and coastal cliffs in the Balearic Islands. Breeding colonies are relatively small, from isolated nests to loose aggregations of 10s or even a few 100s of breeding pairs (Ruiz and Martí 2004). The species is very philopatric, as is the rule with Procellariiformes. Adults do not commence breeding until their third year at the earliest, although most breeding recruitment tends to occur between 4 and 6 years (Oro et al. 2004, Genovart et al. 2016). Birds lay eggs in early-mid March (exceptionally late February); hatching occurs in late April-early May; and adults leave the colonies around late June, a few days before the chicks fledge (early July) (Ruiz and Martí 2004, Tan 2016). 

The species has been recorded diving to more than 35m (Meier 2015). Pelagic prey (especially small pelagic fish) seem to be the main food source for the species. It can also feed on planktonic organisms, and makes extensive use of discards both in the Mediterranean and when in the Atlantic (Le Mao and Yésou 1993, Arcos et al. 2000, Arcos and Oro 2002, Navarro et al. 2009, Louzao et al. 2011b, 2015, Bonnin 2016, Meier et al. in press). Fishing discards do though influence aspects of their ecology such as trophic (Navarro et al. 2009; Käkelä et al. 2010) and movement ecology (Bartumeus et al. 2010), as well as potentially impacting life history traits (e.g. Louzao et al. 2006b, Genovart et al. 2016). 

At sea, it has a rather coastal distribution, and tends to select productive shelf areas most often related to oceanographic frontal systems (Louzao et al. 2006, Louzao et al. 2012, Oppel et al. 2012, Pérez-Roda 2015, Afán 2016). During breeding, birds tend to forage over the closest productive grounds to their breeding colony (Louzao et al. 2011a, Meier et al. 2015) coinciding with favourable winds during the outward stages of foraging trips (Afán 2016). Some individuals also head to productive areas at the extreme of their distribution, assisted by optimal winds during short time windows (Afán 2016). These productive waters are rich in small pelagic fishes (e.g. Palomera et al. 2007), where different types of fishing activity also co-occur and can provide substantial amounts of discards to shearwaters (Arcos and Oro 2002). The species appears to be more coastal during the non-breeding period (Arcos and Oro 2002; Mouriño et al. 2003; Arcos et al. 2012a; Oppel et al. 2012), forming large aggregations that vary in location between (and within) years, presumably due to fluctuations in the availability of schools of small pelagic fish (e.g. Le Mao and Yésou 1993).


This is a long-lived species and therefore the main threats to this species identified are those causing adult mortality. Adult survival is the main conservation concern, as this is unusually low for a Procellariiform (Oro et al. 2004, Genovart et al. 2016). The greatest threat at present is incidental capture by artisanal fisheries. Bycatch affects both adults and immatures, throughout the species’ range, and has been shown to be the main driver of the decline of the species, with almost 50% of the mortality being caused by this factor (Genovart et al. 2016). Small scale vessels have been found to have an average bycatch rate almost 100 times higher than that observed on board medium-scale vessels (Tarzia et al. 2017). Demersal longlining seems to be the most problematic gear causing bycatch, although other fishing gears have been shown to also capture birds, and could have severe effects at the population level, including purse-seine, pelagic longlining and trawling (Arcos et al. 2008, Abelló and Esteban 2012, Boué et al. 2013, ICES 2013, Oliveira et al. 2015). The species' gregarious behaviour and its close association with fishing boats while seeking discards means that occasional mass mortality is likely to occur when long-line boats fish close to flocks (Arcos et al. 2008, Laneri et al. 2010, García-Barcelona et al. 2010). Hence, bycatch appears to be fairly common, but often occurs on an irregular basis, suggesting that estimates derived from observations on a limited number of trips on board fishing vessels could be largely underestimated. Increasing evidence on this has been compiled in the last few years, with events of up to a hundred or more birds caught in a single event (Louzao et al. 2011, ICES 2013, Oliveira et al. 2015).

Predation by introduced mammals is a major global concern for seabirds (Jones et al. 2008, Croxall et al. 2012), and a serious threat for this species. Black Rats Rattus rattus and Brown Rats R. norvegicus, Feral Cats Felis catus and Common Genets Genetta genetta are present in c. 25% of the colonies and affect c. 38% of the breeding population (Arcos and Oro 2004, Ruiz and Martí 2004, Arcos et al. 2012c). Cat predation is thought to drive rapid declines locally and genets are occasional visitors with less clear levels of impact. The presence of rats is more widespread but has a lower impact, putatively affecting only breeding performance (depredating eggs and chicks, but not affecting adult mortality). Permanent monitoring programmes should be implemented to facilitate early detection of alien species in reference colonies.

Due to the congregatory behaviour of the species, acute pollution events, such as oil spills, also pose a serious threat, as a large number of casualties could result from a spill occurring in a congregation area (Ruiz and Martí 2004, Gutiérrez 2011). Other threats include: the reduction of prey due to fishing overexploitation; a potential reduction in fishing discards (an alternative to the overexploited natural prey) and/or anthropogenic environmental change (Arcos 2011a) involving habitat degradation and disturbance in breeding grounds; background pollution (Oro et al. 2008); the development of marine windfarms (Arcos 2011a); light pollution which may disorientate and ground fledglings (Rodríguez et al. 2015) and plastic pollution (Codina-Garcia et al., 2013, Bonnin 2016). Predation by Peregrine Falcons Falco peregrinus in the breeding colonies has also been recently reported (García 2009, Wynn et al. 2010), though this should be considered as a factor of natural mortality that likely has little influence on the decline of the species. The gradual northward movement of the non-breeding population may be affecting immature and adult survival, and this shift may be due to climate change or alterations in fish distributions as a result of fisheries' activities (Yésou 2003, Wynn et al. 2007). The recent demographic decline has not yet decreased the species' genetic variability, and connectivity found among colonies at least does not exacerbate the species' extinction risk (Genovart et al. 2007). 

Conservation actions

Conservation Actions Underway
All breeding sites are currently protected as Special Protection Areas (SPAs) under the Natura 2000 network, with the unique exception of the colony of Punta Prima in Formentera, where new information has revealed that the prevailing colony lays right outside the SPA (and the overlapping Important Bird Area, IBA) designated for this species (Arcos 2011a). The management plans for the Balearic SPAs have not been implemented yet, and so plans are therefore limited to colonies covered by other designations, such as the National Park of Cabrera, the Natural Park of Sa Dragonera and Reserves Naturals des Vedrà, es Vedranell i els illots de Ponent, among others. Rat eradication campaigns have been conducted at several colonies, including Cabrera archipelago and Dragonera Island, where, after a programme of aerial bait drops in 2011, no rats or mice had been detected (Mayol et al. 2012). Less effort has been directed at the most concerning colonies where carnivores are present (e.g. Formentera and Menorca). 

At sea, the Spanish Government designated in 2014 a network of marine SPAs taking as a reference the inventory of marine IBAs conducted by SEO/BirdLife (Arcos et al. 2009). Portugal also designated a few SPAs on the mainland coast recently, including congregatory areas for the Balearic shearwater previously identified as IBAs by SPEA (Ramírez et al. 2008). France has also proposed a network of SPAs that include hotspots for the species. However, management plans for all the marine SPAs are still pending. Finally, evidence gathering for potential at-sea concentrations which could form SPA proposals are underway in the UK. 

Action Plans for the species have been published at local, national or international level in 1991, 1999, 2004, 2005 (Jones et al. 2008) and 2011 (Arcos 2011). A LIFE project for the species ran from 1991-2001 (Ruiz and Martí 2004), and Spain and Portugal had a joint LIFE project running from 2004-2008 aimed at identifying marine IBAs, including for this species (Ramírez et al. 2008, Arcos et al. 2009). A number of actions have been implemented through Species Guardians SEO/BirdLife and SPEA as part of BirdLife's Preventing Extinctions Programme including: coordinated coastal and boat-based counts, gathering information to assess the impact of bycatch on the species, communicating and disseminating information on the species and contributing to the updated Species Action Plan published in 2011 (SEO/Birdlife and SPEA 2013). 

For demersal longlines, the most alarming fishery in the Mediterranean, significant work has been conducted in recent years at assessing the problem (García-Barcelona et al. 2010, Laneri et al. 2010, Cortés et al. in prep) and testing potential mitigation measures (Cortés and Gonzalez-Solís in prep), with nocturnal setting being a good candidate to minimize bycatch. However, work by BirdLife’s Seabird Task Force (STF) is studying the feasibility of implementing such measures, as well as other alternatives, with the aim of pushing for the adoption of an agreed solution in the near future, and has instead found that vertical longlines may be the best approach (Tarzia et al. 2017). The STF has also conducted engagement work with the fishing sector, conducting observations on board vessels and providing self-reporting logbooks (Tarzia et al. 2017).

Despite the above advances, there is an overall lack of proper monitoring and conservation action by the relevant administrations. Most research, conservation and monitoring at present are conducted thanks to the initiative of a few research centres and NGOs (particularly BirdLife partners). This work includes bycatch assessment (questionnaires, onboard observers) and evaluation of mitigation measures, the identification of hotspots at sea through boat surveys, coastal counts and tracking studies (breeding and non-breeding grounds), and breeding monitoring and population demography assessment.

Conservation Actions Proposed
Create a working group for the conservation plan, involving local and national bodies including representatives of the fishing industry. Thoroughly study the problem of bycatch by fisheries, plus implement appropriate mitigation measures throughout the whole distribution range of the species in order to mitigate this threat (i.e. implementation of the EU Seabird Action Plan to reduce bycatch). Control and eradicate introduced predators (with particular emphasis on carnivores) in breeding colonies identified to be at risk. Implement biosecurity measures to prevent introduced predators from re-establishing. Ensure effective protection for nesting sites and marine hotspots, and the implementation of monitoring schemes and management plans, including the monitoring of breeding colonies to estimate demographic parameters. Develop a rapid response plan for a potential oil spill close to main feeding and breeding areas. Continue to raise awareness among the fishing sector, and conduct further engagement with stakeholders. Study small pelagic fish populations in the western Mediterranean and in North East Atlantic (from the NW of Morocco to the English Channel) to assess extent of over-exploitation and how this affects the species. Assess the impact of pollutants and heavy metals on this species. Increase awareness of the negative impacts of light pollution near breeding colonies. Improve understanding of at-sea distribution, including during the non-breeding season. Conduct research to better understand the reasons for the discrepancies between breeding and non-breeding population estimates.


33 cm. Medium-sized, rather dark shearwater. Upperparts dark brown contrasting slightly with the dirty, variably marked brown-whitish underparts. Most individuals show dusky undertail coverts and armpits. Similar spp. Easily told from Manx Shearwater P. puffinus by lack of strong contrast between upperparts and underparts. Dark individuals could be mistaken for Sooty Shearwater P. griseus but always show a white belly patch and lack the scythe-like wings and heavier flight of that species.


Text account compilers
Martin, R., Moreno, R., O'Brien, A., Peet, N., Symes, A., Westrip, J., Hermes, C., Ashpole, J, Calvert, R., Benstead, P., Derhé, M., Fjagesund, T., Bird, J., Harding, M., Lascelles, B.

Guilford, S., Arcos, J.M., Tanner, K., Blasco, J., Oro, D., Andrews, D., McMinn, M., Genovart, M., Porter, R., Louzao, M.

Recommended citation
BirdLife International (2023) Species factsheet: Puffinus mauretanicus. Downloaded from on 03/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from on 03/12/2023.