Balearic Shearwater :: Puffinus mauretanicus

Bad at Goodbyes :: Episode 085

On today’s show we learn about the Balearic Shearwater, a critically endangered migratory seabird who breeds on the Balearic Islands, a Spanish archipelago in the Mediterranean Sea, and who in the non-breeding season migrates to coastlines across Western Europe and North Africa. Its scientific name is Puffinus mauretanicus and it was first described in 1921.

For more information about conservation and protection of the Balearic Shearwater please see SEO Birdlife at https://seo.org/.

• (00:05) Intro
• (02:05) Species Information
• (26:58) Citations
• (29:08) Music
• (36:31) Pledge

Research for today’s show was compiled from:

• Arcos, J.M. (compiler) 2011. International species action plan for the Balearic shearwater, Puffinus mauretanicus. SEO/BirdLife & BirdLife International. - https://acap.aq/advisory-committee/ac6/ac6-information-papers/155-ac6-inf-04-balearic-shearwater-action-plan/file
• Arcos, J. M., & Oro, D. (2002). Significance of fisheries discards for a threatened Mediterranean seabird, the Balearic shearwater Puffinus mauretanicus. Marine Ecology Progress Series, 239, 209–220. https://doi.org/10.3354/meps239209
• BirdLife International. 2018. Puffinus mauretanicus. The IUCN Red List of Threatened Species 2018: e.T22728432A132658315. – https://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T22728432A132658315.en
• de la Cruz, A., Pereira, J. M., Arroyo, G. M., Ramos, J. A., Alonso, H., Arcos, J. M., Rodríguez, B., Bécares, J., Ramos, F., Tornero, J., Saavedra, C., Vázquez, J. A., García-Barón, I., Astarloa, A., Louzao, M., Laran, S., Dorémus, G., Waggitt, J., & Paiva, V. H. (2025). Global distribution, threats and population trends of the critically endangered Balearic shearwater Puffinus mauretanicus. Biological Conservation, 305, Article 111047. – https://doi.org/10.1016/j.biocon.2025.111047
• eloisa matheu. Sound Recording. 2020. Xeno-Canto. XC580250. – www.xeno-canto.org/580250
• Guilford, T., Wynn, R., McMinn, M., Rodríguez, A., Fayet, A., Maurice, L., Jones, A., & Meier, R. (2012). Geolocators reveal migration and pre-breeding behaviour of the critically endangered Balearic shearwater Puffinus mauretanicus. PLoS ONE, 7(3), e33753. – https://doi.org/10.1371/journal.pone.0033753
• iNaturalist – Balearic Islands threatened species
• Kirwan, G. M., J. del Hoyo, N. Collar, and T. S. David (2021). Balearic Shearwater (Puffinus mauretanicus), version 1.1. In Birds of the World (B. K. Keeney, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. – https://doi.org/10.2173/bow.balshe1.01.1
• Lewin, P. J., Wynn, J., Arcos, J. M., Austin, R. E., Blagrove, J., Bond, S., Carrasco, G., Delord, K., Fisher-Reeves, L., García, D., Gillies, N., Guilford, T., Hawkins, I., Jaggers, P., Kirk, C., Louzao, M., Maurice, L., McMinn, M., Micol, T., Padget, O. (2024). Climate change drives migratory range shift via individual plasticity in shearwaters. Proceedings of the National Academy of Sciences, 121(6), Article e2312438121. – https://doi.org/10.1073/pnas.2312438121
• Meier, R. E., Votier, S. C., Wynn, R. B., Guilford, T., McMinn Grivé, M., Rodríguez, A., Newton, J., Maurice, L., Chouvelon, T., Dessier, A., & Trueman, C. N. (2017). Tracking, feather moult and stable isotopes reveal foraging behaviour of a critically endangered seabird during the non-breeding season. Diversity and Distributions, 23(2), 130–145. – https://doi.org/10.1111/ddi.12509
• Oro, D., Aguilar, J. S., Igual, J. M., & Louzao, M. (2004). Modelling demography and extinction risk in the endangered Balearic shearwater. Biological Conservation, 116(1), 93–102. – https://doi.org/10.1016/S0006-3207(03)00180-0
• OSPAR Commission. (2022). Status assessment 2022 - Balearic shearwater. OSPAR Assessments. – https://oap.ospar.org/en/ospar-assessments/committee-assessments/biodiversity-committee/status-assesments/balearic-shearwater/
• Ramírez-Bal, M., García-Barón, I., García, D., Arcos, J. M., Carrasco, G., Lewin, P., Delord, K., & Louzao, M. (2026). Individual migratory patterns of the critically endangered Balearic shearwater: A multi-colony and multi-year study in the NE Atlantic. Global Ecology and Conservation, 65, Article e03989. – https://doi.org/10.1016/j.gecco.2025.e03989
• Rodríguez, A., D. García, B. Rodríguez, E. Cardona, L. Parpal, and P. Pons. 2015. "Artificial lights and seabirds: is light pollution a threat for the threatened Balearic petrels?" Journal of Ornithology 156 (4): 893-902. – https://doi.org/10.1007/s10336-015-1232-3
• Wikipedia – https://en.wikipedia.org/wiki/Balearic_shearwater
• Yésou, P. (2006). The Balearic shearwater Puffinus mauretanicus: A review of facts and questions. Atlantic Seabirds, 8(1/2), 73–79. – https://natuurtijdschriften.nl/pub/546216

Please find us on the web at Bad at Goodbyes and on instagram. Please subscribe and rate/review Bad at Goodbyes wherever you listen to podcasts. Please help spread the word about the show and about the species we feature. Please take care of each other, and all of our fellow travelers.

A note on accuracy: I strive for it! These episodes are well-researched and built from scholarly sources, hoping to provide an informed and accurate portrait of these species. That said, I’m a musician! I am not an academic and have limited scientific background. I may get things wrong! If you are using this podcast for scholarship of any kind, please see the cited sources and double-check all information.

Welcome to Bad at Goodbyes.

On today’s show we consider the Balearic Shearwater.

The Balearic Shearwater is a critically endangered migratory seabird who breeds on the Balearic Islands, a Spanish archipelago in the Mediterranean Sea, and who in the non-breeding season migrates to coastlines across Western Europe and North Africa. Its scientific name is Puffinus mauretanicus and it was first described in 1921.

The Balearic Shearwater is a medium-sized seabird, measuring about 14 inches in length, beak to tailfeather, weighing about a pound, with a roughly 32 inch wingspan. Their plumage is muted browns and tans, the upperparts a darker brown across the primary flight feathers and the tail. Their belly is a pale cream; the breast, flanks, and throat are tan-ish tending slightly paler on the breast. Their skinny black beak is hooked at the tip, with two tube-like nostrils, called nare on the upper ridge of the beak, used to expel excess salt.

Their legs and feet are brown-ish with webbed blackish-tipped toes and are positioned far back on their body. This is an anatomical adaptation for swimming and diving, the rearward placement of the legs aids in propulsion through the water (imagine kicking your legs behind you with your torso on a float, or a rear-mounted paddle on a boat). And so with this rearward limb arrangement, Balearic Shearwater are adept divers. Tracking studies have recorded dives as deep as 98 feet beneath the water's surface.

But this pelvic and leg placement presents a kind of compromise as the shearwater's center of gravity is shifted, they are top heavy, and so it is anatomically difficult to stand and walk. They are slow on land, shuffling a low waddle, their belly and breast almost scraping the ground.

Balearic Shearwater anatomy also presents specialized adaptations for flight, achieving air speeds of roughly 30 miles an hour, through a combination of flapping and gliding on ocean wind currents. They glide with their wings held stiff and straight out from the body, using what's called a "shearing" technique, tilting their bodies so one wingtip skims just above the water's surface while the other points skyward; a streamlined sideways weaving on updraft between the waves.

Their pectoral muscles are divided. The large, superficial pectoralis powers active flapping. And beneath, their deep pectoralis is composed of what's called "slow-tonic muscle fibers" specialized muscles used, during gliding, to lock the wings in a rigid horizontal position without experiencing muscle fatigue.

These adaptations are related to their habitats, diet, and feeding behaviors. The Balearic Shearwater is a piscivore, they eat fish. It's a diet of small shoaling ocean fish, (shoaling means gathers in schools) like anchovy, sardine, European sprat, sand smelt, as well as squid and krill.

They locate prey generally via olfactory chemoreception, via smell. But indirectly. Balearic Shearwater olfaction is particularly sensitive to dimethyl sulfide, this is a gas emitted when zooplankton feed. And the small ocean fish of the shearwater's diet feeds on zooplankton. So the dimethyl sulfide released by feeding zooplankton provides a kind of indirect target for the bird to locate the schools of its prey who congregate to eat that zooplankton.

Once located, the shearwater relies on visual tracking, and then what's called pursuit diving to capture their prey. Gliding roughly 5 feet above the surface they'll plunge into the water, diving and actively swimming downward to intercept their prey. We have great tracking data about this behavior and know that most dives average about 25 feet, but have recorded deep dives of nearly 100 feet, with a bit over a minute, 66 seconds, spent underwater.

We also have evidence that the Balearic Shearwater has adapted to rely on discards. So in commercial fishing, a discard is the portion of a catch that is unwanted and thrown back into the sea, undersized individuals, low market value species, or perhaps species that that operation is not targeting. So these fish are returned to the water, often dead or dying, and in large volume. So this is an abundant and very easily accessible food source for a seabird, like our Balearic Shearwater. So the bird will track and follow these fishing trawlers. But this is all complicated by the reliance on anthropogenic activity, human behaviors and global market fluctuations. And there's an immediate danger of the bird becoming entangled in commercial fishing nets or hooked on longlines. As well as a longer term danger of these commercial fisheries depleting the shearwater's natural prey, and moving on, no longer providing discards and having exhausted the original food source.

The Balearic Shearwater tends to feed at dawn and dusk, and practices cooperative foraging. Massive flocks will congregate peaceably, and engage in collaborative hunting, plunge and diving, synchronously in mass into schools of fish, as a way to corral the prey.

On land, the shearwater is also gregarious and sociable. They form breeding colonies ranging from a few dozen to up to hundreds of individuals, nesting in caves and crevasses on coastal cliffs. These colonies are energetic, social, active, vibrant and loud. We have a remarkable recording by Eloisa Matheu of a cave colony of Balearic Shearwater on Mallorca. Let's listen:

[sound recording]

So that recording was taken during breeding season and we're hearing courtship. Balearic Shearwater form long-term monogamous pair bonds and demonstrate very high-site fidelity returning to the same mate, and same nesting site, often the same nest, throughout their lives.

Mating season is roughly March to July. The female lays a single, relatively large egg, which is incubated for about two months with both parents sharing incubation and foraging duties. The new chick hatches in late April-early May and both parents continue to provide care, food and protection to the hatchling for another roughly two months at which points the parents begin to depart for their annual migration and the new young fledge, leaving the nest, and leaving the colony entirely independent of their parents. But will return again to their birthplace, once migration season ends.

Juveniles reach reproductive maturity at roughly 3 years old, and the species can live to about 25 years old.

We have fossil evidence of shearwater on the Balearic Island of Ibiza, from the Pleistocene Era, roughly 2 million years ago.

————

In the dream,

A charcoal sea

Lines of waves swirl and twist

This, the Atlantic in its momentous expanse

The churn is specked with tiny dots

Whirlling, streaking, convening in scattering choreographies

And then to dive

To push, to plunge, to vanish into the turbulent deep

There is nourishment in the dark unknown

If only we might risk to seek it.

In the dream.

————

The Balearic Shearwater breeds exclusively on the Balearic Islands, an archipelago in the Mediterranean Sea, governed by Spain. We find breeding colonies near the coast on the five main island groups: Cabrera, Formentera, Ibiza, Mallorca, and Menorca, though roughly half of these breeding colonies congregate on Mallorca.

This is a Mediterranean coastal scrub biome of limestone cliffs, rocky islets, and caves. These islands surfaced roughly 25 million years old when continental plates of Paleozoic rock and Mesozoic marine limestone separated from the Iberian Peninsula. The collision of the African and Eurasian tectonic plates pushed these limestone beds upward into an undersea mountain range. And the distinct islands we see today are the long weathered peaks that have remained above the water's surface.

The Balearic Islands have a typical Mediterranean climate with summer highs averaging in the mid-80s°F and winter lows in the mid-40s°F. Average precipitation is roughly 18 inches per year.

The Balearic Shearwater spends roughly 9 months of the year on the island, then migrate annually to their feeding sites from roughly July to October. They spend these late summer-early autumn months on the Atlantic, living exclusively on the open ocean. They do not come ashore to roost, instead settle directly on the water's surface forming large resting flocks called "rafts" near active feeding sites. Most of these rafts are found off the coast of southwestern Europe, Spain Portugal France, and some flocks have been documented as far north as the waters off of the UK and as far south as the waters off Morocco.

The Balearic Shearwater share their island breeding grounds with:

Yellow-legged Gull, Hermann's Tortoise, Ibiza Wall Lizard, Mediterranean Juniper, Kentish Plover, Spurge Olive, Western Swamphen, European Turtle-Dove, Osprey, Marbled Duck, European Rabbit, Egyptian Vulture, Monarch Butterfly, Ruddy Turnstone, Cirl Bunting, European Pond Turtle, Northern Lapwing, Great Capricorn Beetle, Mallorcan Midwife Toad, Green-winged Orchid, Dune Scarab, Sweet Violet, Meadow Pipit, Canary Island Palm, European Garden Dormouse, Greater Horseshoe Bat, Mediterranean Turtle, Desert Bluebells, European Stag Beetle, River Red Gum, Sweet Pea and many many more.

The Balearic Shearwater population is primarily threatened by interaction with the commercial fishing industry. As mentioned the shearwater congregates and feeds on commercial fishing discards. And roughly half of adult

Balearic Shearwater mortality is from entanglement in the nets and lines of commercial fishing vessels. Relatedly, prey species shortages from long term overfishing is a potential threat.

Human introduced mammals on the Balearic Islands affect over a third of the Balearic Shearwater's breeding population. This is predation by introduced Black Rats, feral Cats, Common Genet, and Pine Martens. Feral cats prey upon adult shearwater and Black Rats feed upon eggs and chicks.

Light pollution on the Balearic Islands is affecting young shearwater, with fledgings found stranded after being attracted to artificial light.

Human induced climate change due to the persistent over-reliance on fossil fuels, is already affecting Balearic Shearwater migratory patterns. Recent studies suggest that climate change is driving a more northward shift in migratory feeding sites. And flying longer and further increases mortality risk and delays their return, affecting breeding timing.

Fortunately, all Balearic Shearwater breeding sites are currently protected as Special Protection Areas and many colonies are located within National Parks, like the National Park of Cabrera, the Natural Park of Sa Dragonera and the Reserves Naturals des Vedrà.

International attention is also being given to the Shearwater's migration routes and feeding sites, with Spain, Portugal designating marine Special Protection Areas off their coastlines.

SEO Birdlife, la Sociedad Española de Ornitología (the Spanish Ornitology Society) is exploring education programs and collaboration with commercial fishies to develop measures to minimize Shearwater entanglement.

Information for today’s show about the Balearic Shearwater was compiled from:

iNaturalist – Balearic Islands threatened species

Wikipedia – https://en.wikipedia.org/wiki/Balearic_shearwater

For more information about conservation and protection of the Balearic Shearwater please see SEO Birdlife at https://seo.org/.

I honor the lives of all Balearic Shearwater. I will commit their name to my record. I am grateful to have shared time on our planet with this being. I lament the ways in which I and my species have harmed and diminished this species. I grieve.

And so, in the name of the Balearic Shearwater I pledge to reduce my consumption. And my carbon footprint. And curb my wastefulness. I pledge to acknowledge and attempt to address the costs of my actions and inactions. And I pledge to resist the harm of plant and animal kin and their habitat, by individuals, corporations, and governments.

I forever pledge my song to the witness and memory of all life, to a broad celebration of biodiversity, and to the total liberation of all beings.