Māmane woodlands are home to a wide variety of native arthropods (insects, spiders), the native Hawaiian hoary bat (Lasiurus cinereus semotus), and several native bird species, including the Palila (Loxioides bailleui), ‘Amakihi (Hemignathus virens), ‘Apapane (Himatione sanguinea), ‘Elepaio (Chasiempis sandwichensis sandwichensis), ‘Akiapola‘au (Hemignathus munroi), and ‘I‘iwi (Vestiaria coccinea). Of these species only the Palila, ‘Amakihi, ‘Apapane and ‘I‘iwi have been observed at Halepōhaku in recent times. Māmane trees are the primary food source for birds in the region, providing nectar and seeds on a seasonal basis.
Several bird species also prey on the insects that inhabit the māmane trees. Perhaps the most notable is the Federally Endangered Palila (Loxioides bailleui). Palila feed on the green seedpods of māmane trees, moth larvae, caterpillars, naio fruits, as well as other vegetation. These unique birds were once common in lowland dry forests on several of the Hawaiian Islands, but due to habitat alteration first by humans, and subsequently by grazing mammals, their range has decreased to a small band around Maunakea, in the last remaining stands of Māmane woodlands.
The alpine shrublands and desert are home to only a few animals. One Federally Endangered bird, the Hawaiian petrel or ‘Ua‘u (Pterodroma sandwichensis), has been observed in subalpine lava flows on Mauna Loa at 8,000 – 9,200 ft elevation, and occasionally in subalpine and alpine habitats on Maunakea. It has not however, been spotted near Halepōhaku or the Maunakea Science Reserve in recent times.
Much more common are arthropods, including species blown up the mountain from lower elevations and die in the cold (referred to as aeolian drift) and cold-adapted residents that feed on the dead and dying arthropods found in aeolian drift or on one-another. The arthropod community on the summit is highly unusual in that it is mostly made up of predators and scavengers, with very few species that rely on plants as their sole food source.
Through the various studies conducted at the summit of Maunakea, 21 resident species, and 14 species of undetermined origin (unknown if they are resident or aeolian) have been recorded in the alpine stone desert. Native resident species include the Wēkiu bugs (Nysius wekiuicola), a noctuid moth (Agrotis sp.), a hide beetle (Dermestes maculatus), a large wolf spider (Lycosa sp.), two sheet web spiders (Erigone species), an unidentified Linyphiid sheet web spider (Family Linyphiidae), two unknown Entomobryid springtails (Family Entomobryidae), a Collembolla springtail (Class Collembola, family and species unknown), two species of mites (Families Anystidae and Eupodidae), a bark louse (Palistreptus inconstans) and a centipede (Lithobius sp.). Non-native resident species include a book louse (Liposcelisdivinatorius), big-eyed bug (Geocoris pallens), a hunting spider (Meriola arcifera), a sheet web spider (Lepthyphantes tenuis), and an unidentified jumping spider (family Salticidae).
The Wēkiu bug (Nysius wekiuicola) is the best-studied invertebrate at the summit. First recognized as a new species in 1979, the Wēkiu bug is a true bug in the family Lygaeidae (order Heteroptera), it is approximately the size of a grain of rice. The Wēkiu bug, and its sister species, the Mauna Loa bug (Nysius a'a), which resides at the high elevation areas on Mauna Loa, differ from other species in the genus Nysius in being scavengers and predators of dead and dying arthropods, while all other known species in the genus are seed and plant feeders. Wēkiu bugs reside in the cinders on the summit of Maunakea, where they use their straw like beaks to suck the hemolymph (blood) from dead and dying. They do not appear to feed on healthy or living individuals of the other resident arthropod species.
Wēkiu bugs are most abundant on cinder cones that formed nunataks (ice free areas rising above the surrounding glacier) or that lay at the glacier limit during the last glaciation, especially on the north- and east-facing slopes (and on slopes shaded from the intense sun), where seasonal snow remains the longest. They can also be found on the flanks and at the bases of the cones where cinders have accumulated to sufficient depths. Snowfields may be important to the scavenger species on the summit, as they chill and store insects in the aeolian drift for later consumption. Wēkiu bugs can often be seen foraging on the edge of snow banks. Crests of glacially overridden cones and inter-cone expanses of glacial till appear to lack suitable Wēkiu bug habitat.