After spending a period of recovery time in France, he embarked on a ship to Tahiti, where he collected malacological and ornithological specimens.
[1] In 1858 he travelled to New Caledonia, where with botanist Eugène Vieillard, he explored little-known regions of the island.
The following year, he departed the colony with a large collection of natural history specimens — birds from the expedition were later studied by ornithologists Jules Verreaux and Marc Athanase Parfait Oeillet Des Murs.
After his return to France, he worked on "Essais sur la Nouvelle Caledonie", a book co-authored with Vieillard, and first published in 1863.
Subsequently, he returned to New Caledonia with Vieillard, where in Noumea, the pair split company, with Deplanche journeying to Lifou in the Loyalty Islands.