It is estimated that one species colonized the Hawaiian Islands every 30-35 thousand years prior to discovery by humans according to A. Ziegler in his book Hawaiian Natural History, Ecology, and Evolution (2002).
The Hawaiʻi Biological Survey (HBS) is an ongoing natural history inventory of the Hawaiian archipelago. It was created to locate, identify, and evaluate all native and non-native fauna and flora within the state, and to maintain the reference collections of that biota for a wide range of uses. It is available here: http://hbs.bishopmuseum.org/. The page does have a link for endangered species but those pages are long out of date as of a May 2020 check.
Below is a summary table of species numbers modified (see footnotes of table) from A. Allison, 2002, ‘Biological surveys – new perspectives in the Pacific’ in the journal Org. Divers. Evol: https://www.sciencedirect.com/science/article/pii/S1439609204700616?via%3Dihub.
The most recent published tally, both by Allison (2002) and Eldredge and Evenhuis (2003), lists 23,680 terrestrial species of which 9,307 are endemic. However, there apparently are marine species included in the fish and mammal categories (see table and footnotes), and with these removed (and algae and protists) the numbers are 20,238 terrestrial species, of which 9,164 are endemic. Although the original numbers for plants in the tables of the two sources have been retained for purposes of the table below, those numbers have been revised based on new data that have published and they are summarized on the flora page.
New records are added to the HBS data annually and are available here: http://hbs.bishopmuseum.org/hbspubs.html and the latest index, published in 2015, is available at: http://hbs.bishopmuseum.org/pubs-online/pdf/op117.pdf.
Hawaiʻi is known for its endemic flora and fauna. Endemism for Hawaiian vascular plants and insects are especially high at 90 and 94%, respectively (see table below).
A list of endemic plants and animals by category is on Wikipedia, although the list is far from complete: https://en.wikipedia.org/wiki/Endemism_in_the_Hawaiian_Islands. Another Wikipedia list of endemic fauna, is here: https://en.wikipedia.org/wiki/Category:Endemic_fauna_of_Hawaii. Yet another page lists the 71 known taxa of birds endemic to the Hawaiian Islands: https://en.wikipedia.org/wiki/Endemic_birds_of_Hawaii. Subgroups and individual species listed on all those pages have links to their pages.
It is interesting that even within the islands of Hawaiʻi, many of the endemic species are not found on all the main islands and often are present on only one of the islands. In the case of endemic flowering plants fewer than half of those taxa have multi-island distributions.
A comparison of the flora of different Polynesian and Micronesian islands (Micronesia, Marquesas, Society Island, Fiji, Samoa, Tonga), that includes Hawaiʻi, from data in the paper by Costion and Lorence (2012) in The Endemic Plants of Micronesia: A Geographical Checklist and Commentary (http://www.micronesica.org/sites/default/files/3_costion.lorence_micronesica_431.pdf) shows that Hawaiʻi has by far the greatest percentage of endemism of any island group in the comparison (88%), however the lowest number of native species per area (native species richness) of the islands compared and lower than all the areas except Tonga for endemic species richness.
Species of Greatest Conservation Need
Hawaiʻi has a Statewide Wildlife Action Plan (SWAP) dated 2015 in which are designated Species of Greatest Conservation Need (SGCN; under a federal program for all states). The complete plan is at https://dlnr.hawaii.gov/wildlife/files/2016/12/HI-SWAP-2015.pdf.
The 2015 SWAP provides a status of Hawaiʻi’s native terrestrial species. The document designates the following terrestrial and freshwater SGCN and associated numbers: terrestrial mammal (1), birds (78), terrestrial invertebrates (~5,000), freshwater fishes (5), freshwater invertebrates (12), anchialine pond-associated fauna (20), and flora (over 756). Individual fact sheets are provided to summarize information for the more well-known species and fact sheets for lesser known groups (e.g. fauna orders) are provided for the remainder for a total of 200 terrestrial and freshwater fauna fact sheets. The fact sheets are here: https://dlnr.hawaii.gov/wildlife/hswap/fact-sheets/. Links to specific groups are below.
- Stylommatophora, Archaeogastropoda (land snails)
- Acari (mites and ticks)
- Araneae (spiders)
- Archaeognatha (bristlethighs)
- Coleoptera (beetles)
- Collembola (springtails)
- Dermaptera (earwigs)
- Diptera (true flies)
- Heteroptera (true bugs)
- Homoptera (aphids, plant/leaf hoppers, psyllids, mealybugs, etc.)
- Hymenoptera (bees and wasps)
- Lepidoptera (moths and butterflies)
- Neuroptera (lacewings, antlions)
- Odonata (damselflies, dragonflies)
- Orthoptera (grasshoppers, crickets, katydids)
- Phthiraptera (lice)
- Psocoptera (bark lice, psocids)
- Siphonaptera (fleas)
- Thysanoptera (thrips)
- Isopoda (pillbugs, sowbugs)
- Geophilomorpha, Lithobimorpha (centipedes)
- Polyxenida, Spirostreptida (millipedes)
Genetic Safety Net Species are identified in the SWAP and are defined as plants with less than 50 individuals left in the wild. A more updated list and other information is provided on the Hawaiʻi Plant Extinction Prevention website here: http://www.pepphi.org/. The website (as of December 2019) indicates that there are currently 220 plant species that have have fewer than 50 wild individuals remaining.