[citation needed] Two small and at least temporarily brackish pools are the only source of fresh water; even these may dry up in summers with little rain.

[3] The Handbook of Selected Pacific Islands (1959), by Edwin B. Doran, observed that "Clarion has never been occupied by man for more than a few days at a time", adding that "there are no facilities of any sort at present.

The island is near the north(east)ern limit of the breeding range of several of these, but their continued presence needs confirmation: For reasons not fully known, Clarion seems to be more attractive to shorebirds and other vagrant or migrant birds than Socorro; perhaps this is due to the presence of red-tailed hawks on the latter island.

Great blue heron, snowy egret, white-faced ibis, Pacific and possibly American golden plover, spotted sandpiper, wandering tattler, ruddy turnstone, black-necked stilt, western gull and barn swallow are examples of the species that can be encountered on Clarion with some regularity; most of the shorebirds congregate in the sheltered shallows of Sulphur Bay.

If the Revillagigedos population is indeed distinct, it might be endemic of Clarión as the only other local subpopulation, on San Benedicto, was destroyed by a volcanic eruption on August 1, 1952;[2] on the other hand, mainland birds have sometimes been assigned to clarionensis also.

The Clarión population of the critically endangered Townsend's shearwater (Puffinus auricularis) was probably extirpated in 1988 due to the feral pigs' depredations on the young and nesting birds.

insularis, Cyperus duripes, Euphorbia anthonyi, Nicotiana stocktonii, Perityle socorrosensis, Spermacoce nesiotica and Zapoteca formosa ssp.