[4] The Fiordland crested penguin was described in 1845 by English zoologist George Robert Gray, its specific epithet derived from the Ancient Greek pachy-/παχυ- "thick" and rhynchos/ρύγχος "beak".

[14] Eudyptes pachyrhyncus are split into three groups based on their location in the fjord and where they hunt, dubbed the inner-fjord, mid-fjord and outer-fjord.

[15] Outer-fjord Eudyptes pachyrhynchus make long, deep dives with descent velocities reaching higher points than that of mid-fjord individuals who forage in the upper 20 meters of the water column[15].In isolated populations of the species patterns in autochthonous food sources and subsidies from allochthonous resources impact the population and locally produced resources are of great importance to each and every colony.

[18] Except for during the reproductive and incubatory periods Fiordland crested penguins tend to travel alone and are nocturnal creatures during their entire life.

[6] Considered sexually mature at around 5 to 6 years post birth Eudyptes pachyrhynchus proceed to participate in their first breeding cycle.

[22] Eudyptes pachyrhynchus nest in small scattered groups across steep slopes covered by rainforests that protect them from extreme temperatures[18] and on open coast sites such as Jackson Head.

[24] The incubation period lasts for 31–36 days and both parents take long shifts with the male guardian for three weeks while the female feeds the hatchling near daily.

[24] Heavy rainfall and frequent storms play a large role in loss of offspring while if both eggs are hatched the larger one is favoured leading to increased mortality rates of the smaller penguins due to starvation.

[22] During chick rearing the Eudyptes pachyrhynchus penguins shift to central-place foraging strategies as they depend on reliable access to prey while avoiding straying too far from suitable nesting habitats.

[29] Fiordland crested penguins are classed as near threatened by the IUCN,[1] and their status was changed from vulnerable to endangered by the Department of Conservation in 2013.