[11] This same suite of rocks can also be traced eastwards on the mainland along the northern side of the Marloes peninsula and extends almost as far east as St Ishmael's.

A NW-SE aligned fault stretches between Bull Hole and South Haven, offsetting the strata on either side.

Airborne laser scanning together with ground excavations continued in 2016 and established that human settlement dates back 5,000 years.

[17] Skomer is best known for its large breeding seabird population, including Manx shearwaters, guillemots, razorbills, great cormorants, black-legged kittiwakes, Atlantic puffins, European storm-petrels, common shags, Eurasian oystercatchers and gulls, as well as birds of prey including short-eared owls, common kestrels and peregrine falcons.

The island is also home to grey seals, common toads, slow-worms, a breeding population of glow-worms and a variety of wildflowers.

By 2004, there were numerous puffin burrows on the island and adults flying back with food run across the walkways oblivious to the tourists.

[20] Shearwaters are not easy to see as they come and go at night, but a closed-circuit television camera in one of the burrows allows subterranean nesting activity to be seen on the screen in Lockley Lodge on the mainland at Martin's Haven.

As they are ungainly and vulnerable on the land, they leave their burrows only at night to avoid predation by gulls also breeding on the island.

The lack of land-based predators on the island means that the bracken habitat is an ideal place for the vole, with the population reaching around 20,000 during the summer months.

Then the resident short-eared owls may be seen patrolling the areas close to the farmhouse in the centre of the island for voles to feed their young.

The lower littoral zone is dominated by Hydropunctaria maura and associated species, forming a black crust on wave-exposed rocks.

In areas with high levels of seabird activity, nitrogen- and phosphorus-rich guano influences the composition of lichen communities, promoting the growth of species such as Xanthoria parietina and Candelariella coralliza on bird-perching rocks.

The island's geological diversity, with acid rhyolites, basaltic lavas, and quartz conglomerates, further contributes to the variety of lichen habitats.

Monitoring programs have been established to track long-term changes in lichen populations, particularly in response to fluctuations in seabird numbers and environmental disturbances such as oil pollution.

The 1996 Sea Empress oil spill raised concerns about potential impacts on Skomer's maritime lichens, highlighting the need for ongoing conservation efforts.

Overnight guests are brought over on a separate boat trip on the morning of their stay and the hostel is open April to September.