Balearic Shearwater Diet and Size: Feeding Habits, Predators, and Measurements

Balearic Shearwater Diet and Size: Feeding Habits, Predators, and Measurements

The Balearic Shearwater, a small seabird with stiff wings, breeds on islands located in the western Mediterranean. In late summer and autumn, these birds head to offshore areas in Britain and southwest Europe. 

Though often compared to Manx Shearwaters due to their similar shape and size, the Balearic Shearwater is dark brown above and a dull pale brown below, often featuring a white belly, unlike the distinct black-and-white pattern of the Manx.

The Dietary Habits Of The Balearic Shearwater 

Let’s look at the dietary preferences of the Balearic Shearwater, including their hunting methods and feeding practices for their young.

What Does A Balearic Shearwater Eat?

Small fish such as sardines, herring, anchovy, and sprat form the staple diet of Balearic shearwaters, with additions of small crustaceans, squid, and offal from fishing boats. 

While they occasionally follow ships to feed on discards, they mainly depend on their natural ability to hunt live fish and small crustaceans. This behaviour could change based on the availability of fishing activities and location.

What To Feed A Baby Balearic Shearwater? 

In their first two weeks, Balearic shearwater chicks mainly receive anchovies from their parents as food.

Breeding Habits Of Balearic Shearwaters

Balearic Shearwater

The breeding season for Balearic shearwaters spans from February to June. Following their breeding period, they leave the Mediterranean for Atlantic waters, moulting around Portugal, Spain, and within the Bay of Biscay. 

After moulting, most shearwaters head back to the Mediterranean, often by the late autumn, though many spend the winter off the Spanish Atlantic coast.

Do Balearic Shearwaters Mate For Life?

Balearic shearwaters often stay with the same mate for a long time and come back to the same colonies they used before to breed. They sometimes take breaks from breeding, called “sabbatical years”. 

Despite showing behaviours of long-term pair bonds, such as returning to the same breeding sites, the presence of these sabbatical years suggests that their partnerships might not be lifelong.

The Size & Weight Of Balearic Shearwaters

Balearic Shearwater - Puffinus mauretanicus

Next, let’s take a look at the measurements of the Balearic Shearwater, focusing on both their weight and the span of their wings.

How Much Does A Balearic Shearwater Weigh?

A Balearic Shearwater’s weight falls between 472 grams and 565 grams, or about 16.6 to 19.9 ounces. 

These shearwaters are larger compared to their relative, the Manx shearwater. Typically, females are lighter and smaller than males, but sizes may vary, with some females being larger and some males smaller.

How Big Is A Balearic Shearwater?

A medium-sized seabird, the Balearic Shearwater, is typically found measuring between 34 and 39 cm (13.4 to 15.4 inches) long, and boasts a wingspan ranging from 78 to 90 cm (30.7 to 35.4 inches).

Are Balearic Shearwaters Under Threat?

Flying Balearic Shearwater

The Balearic shearwater was listed as Critically Endangered globally by the IUCN in 2004. This was after finding out the bird population was falling sharply, mainly from sea threats. Observations showed a decrease in important non-breeding areas, such as Western France. 

Upon being listed, the species was regarded as sensitive because it struggles with human activity, behavioural and ecological traits (for instance, its coastal habitat and habit of forming large groups), and influenced by its life history (being long-lived and reproducing slowly).

What Eats A Balearic Shearwater?

Both on land and at sea, the Balearic Shearwater faces significant threats. In some of its breeding locations, it is endangered by feral cats (which prey on chicks and adults) and by rats (which prey on eggs and chicks), thus lowering its breeding success. 

Additionally, light pollution in cities can cause young birds to become disoriented. In the past, these birds were also taken for human consumption.

Where can I see Balearic Shearwaters in the UK?

During the warmer months, specifically between July and September, you may have the chance to see Balearic Shearwaters around the southern coastlines of the UK. 

Particularly, these birds are more commonly seen along the southern English coast and the western parts of Wales. Additionally, there are a few noted sightings from the North Sea in the east.

SEE ALSO: Balearic Shearwater Life Cycle: Nest Building To Fledging (and everything in between)

Frequently Asked Questions

What are the predators of the Balearic Shearwater?

The predators of the Balearic Shearwater include feral cats and rats, which prey on chicks and eggs, significantly reducing their breeding success. Additionally, light pollution can disorient young birds, making them more vulnerable.

How big are Balearic Shearwaters?

Balearic Shearwaters are medium-sized seabirds, typically measuring between 34 and 39 cm (13.4 to 15.4 inches) in length, with a wingspan ranging from 78 to 90 cm (30.7 to 35.4 inches).

Why are Balearic Shearwaters endangered?

Balearic Shearwaters are endangered due to several factors, including predation by feral cats and rats, light pollution, and human activities. The IUCN listed them as Critically Endangered in 2004, noting a sharp population decline influenced by their coastal habitat, tendency to form large groups, and slow reproductive rate.

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