Studies of Endangered Species: A collection of twenty-four watercolours for W.H.Hudson and L. Gardiner, 'Rare, Vanishing and Lost British Birds' including: pelicanus onocrotalus (pelican); grus cinerea (crane); platalea leucorodia (white spoonbill); tetrao urogallus (capercaillie); recurvirostra avocetta (avocet); otis tarda (great bustard); limose belgica (black-tailed godwit); alca impennis (great auk); astur palumbarius (goshawk); locustella luscinoides (red night-reeler or savi's warbler); hydrochelidon nigra (black tern); botaurus stellaris (bittern); circus ruginosus (marsh harrier); machetes pugnax (ruff and reeve); circus cyaneus (hen harrier); circus cineraceus (montagu's harrier); pernis apivorus (honey buzzard); pandion haliatus (osprey); sterna dougalli (roseate tern); endromias morinellus (dotterel); gialitis cantiana (Kentish plover); oriolus galbula (golden oriole); and coturnix communis (common quail)

The present collection of watercolours are the artist's original drawings, that were worked up for the plates to illustrate W.H. Hudson's book Rare, vanishing and lost British birds. The collection comprises 23 of the 25 plates that were published and one unpublished watercolour, also by Grønvold.

The book was compiled by Linda Gardiner from notes written by Hudson, in anticipation of publishing an enlarged edition of the pamphlet Lost British Birds, which he wrote in 1894 for the Society (now the Royal Society) for the Protection of Birds. Gardiner writes in her preface to the book 'By the publication....he hoped to arouse public attention and public feeling in regard to the passing of the birds, birds lost to our country, birds threatened, and birds becoming scarce, seeing behind these a dim vista of yet others, and others again, growing fewer and still more few...' (p. ix).

The inscriptions such as 'same size as avocet', 'same size picture as honey buzzard' and 'with stork' offer an insight into the make-up of the book and the size and positioning of the plates in the final publication.

Grønvold was a Danish artist who moved to England and worked on a number of ornithological publications.