Sooty Shearwater Life Cycle: Nest Building To Fledging (and everything in between)

Sooty Shearwaters are sooty brown seabirds that cover large distances travelling over the world’s oceans. Smaller than a Herring Gull, but large for a Shearwater, the Sooty Shearwater has a dark brown body, brown wings and a dark bill.

If you spot one up close, you may notice the pale band running underneath its wings. These fascinating seabirds do not breed in the UK but make massive clockwise rotations up the western Atlantic during spring.

They spend summer in the northern Atlantic then travel into waters off the UK coastline during late summer/early autumn on their return journey to oceans around the Antarctic to breed. To find out more interesting facts about Sooty Shearwaters, keep reading.

How Long Does A Sooty Shearwater Live?

The average lifespan of a Sooty Shearwater is around 20 years. But there have been individual birds that have lived for more than 34 years according to ring records. Their lifespan depends on a number of factors including climatic conditions, pollution, the availability of food and predation.

One of the main predators that affects the numbers of Sooty Shearwaters is man. In particular the Maori population of New Zealand. Around 250,000 Sooty Shearwaters or “Muttonbirds” as they are known, are harvested for oils and food every year by the Maori population.

How Fast Can A Sooty Shearwater Fly?

Known for their long-distance migrations, Sooty Shearwaters typically fly at speeds of around 34 mph (54 km/h) during regular flights. When migrating, Sooty Shearwaters ride on wind currents and include dynamic soaring flight patterns.

During these migratory flights, the Sooty Shearwater can reach speeds in excess of 41.5 mph (67 km/h). These high speeds allow the Sooty Shearwater to cover vast distances in a short space of time.

Are Sooty Shearwaters Aggressive?

Sooty Shearwaters are peaceful birds that feed in oceans and do not defend territories at land or at sea. They nest in large communities with some colonies having as many as 2.5 million birds rearing their chicks in burrows packed tightly next to each other.

What Is A Sooty Shearwater’s Habitat?

Sooty Shearwaters breed in the southern hemisphere close to the ocean in forested or vegetated areas on islands or coastal headlands. They nest in huge colonies in the south Pacific and Atlantic oceans and on islands off Australia, New Zealand and South America.

After the breeding season ends, Sooty Shearwaters fly out to sea where they spend several months at a time. They split their time up with half spent feeding in shallow waters off the continental shelf and the other half flying over pelagic waters. 

How Long Does It Take For A Sooty Shearwater To Build A Nest?

It can take anywhere between a few days or up to 2 weeks for a Sooty Shearwater to build a nest. It all depends on whether the breeding pair use an existing burrow or excavate a new burrow from scratch.

If the pair are creating a new burrow, it will often take 7 to 14 days to complete. Both birds use their bills and feet to dig the burrow which is typically located on a slope or in areas of soft soil. These burrows can extend for around 10 ft (3 metres) underground.

If they are reusing an old burrow, it might only take a few days until it is suitable for rearing their young. Whether they excavate a new burrow or repurpose an old burrow, the pair will line it with grass, leaves and other soft plant materials before the female lays her egg.

Eggs

Once the nest has been successfully dug out and lined with enough nesting materials, the next stage in the reproductive cycle is the egg laying phase.

When Do Sooty Shearwaters Lay Eggs?

Nesting generally takes place between October and May with eggs being laid from late November to early December with the eggs hatching sometime in January.

How Many Eggs Does A Sooty Shearwater Lay?

Sooty Shearwaters lay one egg per brood and only have one brood per season. The pair don’t reach sexual maturity until they are around 9 to 10 years of age.

What Do Sooty Shearwater Eggs Look Like?

Sooty Shearwater eggs are matt (non-glossy) white and measure around 77 x 48 mm in size. The pair only lay one egg which generally ensures that they can successfully raise their chick to the fledgling stage.

How Long Do Sooty Shearwater Eggs Take To Hatch?

Both parents share the incubation of the egg which lasts for around 52 to 56 days. The parents will spend anywhere between 4 to 9 days incubating the egg before swapping with the other parent.

Chicks

Once the egg hatches, we move onto the next stage of the Sooty Shearwater’s life cycle, the chick.

How Many Chicks Does A Sooty Shearwater Have?

As Sooty Shearwaters only lay one egg, it stands to reason that they only have one chick. The majority of chicks survive to the hatching stage and unless one or both parents meet an untimely end, that chick will reach maturity.

When Do Sooty Shearwater Chicks Open Their Eyes?

Sooty Shearwater chicks are altricial which means that when they hatch they are naked, blind and depend on their parents for everything. This includes food, warmth and protection. 

Altricial chicks typically open their eyes from around day 5 to day 7 after hatching. They are cared for by their parents for around 10 weeks and then the parents fly away leaving the chicks to fend for themselves.

When Do Sooty Shearwater Chicks Fledge?

Sooty Shearwater chicks typically fledge the nest around 97 days after hatching. Their parents tend to leave the nests around 7 to 14 days before the chicks.

The chicks then leave their burrows and fly out to sea where they will stay until they are around 5 or even 8 or 9 years old.

Only once they reach the age of sexual maturity will the Sooty Shearwater chick return to land with its partner to breed.

SEE ALSO: Manx Shearwater Vs Guillemot: Key Differences Explained

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