Written By: Leslie Hubert, Biology 487, Autumn 2009
STATUS (IUCN v3.1)
The Yellow-Eyed Penguin population is in decline because their breeding habitat (forest and scrub) is declining in quality due to habitat degradation by human-induced factors such as development and deforestation. Historically, the forest and scrub type habitat is limited in its geographic range throughout New Zealand, amplifying the effects of any habitat degradation on the resident species.
Human: Threats include the introduction of predators, habitat destruction by development and agricultural grazing by livestock, drowning in fishing nets, and accidental fires at or near breeding locations.2, 6, 11, 18
Increased ecotourism can also have behavioral effects on Yellow-Eyed Penguins. For example, penguins are less likely to come ashore when groups of tourists are present, which may cause a decrease in food brought back to chicks during chick rearing. Chick survival is then affected in terms of decreased weight during fledging and increases in nest desertion by mates waiting for the other to return and relieve nest guard duties.9, 14, 15
The recent range expansion of Yellow-Eyed Penguins after the extinction of their sister species, Megadyptes waitaha, suggest that this species has the ability to colonize new areas. However, human-induced threats are preventing any future ability for range expansion.3
Climate variation (past and current): Currently, seasonal climate variations due to El Nino/La Nina events and long term climactic changes are impacting populations. Seasons characterized by increased rainfall and cooler temperatures have shown an increase in populations, while seasons with dry, warm conditions have led to decreases by affecting the breeding success of individuals. The warm, dry seasons correspond to El Nino years, which negatively affect the Yellow-Eyed Penguin’s food supply in the waters off the coast of New Zealand. Over the past few decades, the climate along the southeastern coastline of New Zealand has become progressively warmer and drier. Changes in climate coupled with habitat destruction have led to less forest coverage, which the penguins use as shade during warm conditions. El Nino conditions can cause further stress to penguin populations, which are coping with decreased vegetation coverage leading to breeding failure.
During climate and population studies in the 1930s and 1940s, the reverse situation was found: forest coverage was abundant and populations showed increases during warm, dry conditions, while cold, wet seasons showed decreases in populations. Since vegetation coverage was readily available during warm conditions, there was less stress from the environment on penguin populations. Environmental stressors were then shifted in the opposite direction, during cold, wet seasons leading to decreases in breeding success relative to warm, dry conditions. In addition, due to converging water currents, specifically the north flowing Southland Current, and nutrient rich terrestrial runoff, the waters off of Otago Peninsula are important spawning areas for many fish species in which yellow-eyed penguins feed upon. Seasonal and long term climate changes can affect survival of many of these prey species, in turn affecting penguin populations.12, 13
MITIGATION OF THREATS
What is being done: All New Zealand sub-Antarctic islands were named World Heritage Sites in 1998, allowing for more funding for conservation efforts11. On the Campbell Islands sheep and other livestock grazers are being removed to mitigate habitat destruction from grazing activities11. On Otago Peninsula there are several extensive re-vegetation projects in areas in and around the breeding grounds. Also researchers are providing nest boxes. Trapping of introduced predators is helping to decrease the number of attacks on yellow-eyed penguins. Ecotourism practices are also changing. Tourists now view penguins from areas hidden from the breeding sites. The Yellow-Eyed Penguin Trust in Dunedin, New Zealand, is an essential organization helping to conserve yellow-eyed penguins and their habitat through public education, predator control, habitat restoration (including a plant nursery for re-vegetation source), and various research and census projects.15
What should or could be done: The Yellow-Eyed Penguin’s life at sea is less well known. Areas of future research should include effects of climate change on oceanic productivity off the coast of New Zealand, as well as which predatory species prey on Yellow-Eyed Penguin at sea, in order to better determine the impacts on penguin populations and conservation needs.
Adults: Pale yellow feathers on head, with a distinctive brighter yellow eye band encircling the head, slate grey back and side, white belly.
Juveniles: Back, sides and belly are same as adults. Head plumage different in that the yellow band encircling the head is absent, and the yellow head feathers are paler in color or absent. The throat and chin are mostly white in color. Adult plumage is gained at 14-16 months.
Chicks: Chicks have dark brown down feathers.18
On average, males have a larger bill depth (males: 1.92-2.27 cm, females: 1.80-2.08 cm), and longer head and foot lengths than females.16, 18
Weight: 4.5-6.0 kg
Height: 56-79 cm
Beak: 5.10-5.88 cm
Flipper: 20.7-22.3 cm
Foot: 13.1 cm +/-2.8 cm
Weight: 4.3-5.8 kg
Height: 56.0-79.0 cm
Beak: 4.93-5.78 cm
Flipper: 19.7-21.5 cm
Foot: 12.6 cm +/-2.95 cm
Vocalizations are important for locating mates and offspring because Yellow-Eyed Penguins nest under dense vegetation out of visual range from one another. Vocalizations are also social stimuli and increase nesting synchrony within a colony
Yellow-Eyed Penguins have three types of vocalization: ecstatic, mutual and contact calls. Ecstatic calls are a series of high pitched phrases lasting approximately 25 seconds, and are primarily used by males during courtship and territorial displays. Mutual calls are duets by pairs when locating each other after one mate returns from foraging, and consist of a series of high pitched short syllables lasting approximately 25 seconds. Contact calls are given by individuals on land or at sea and consist of short monosyllables and function in locating each other and in individual recognition.
There are no subspecies, but mainland and island populations are genetically distinct from one another. Recent findings suggest that sub-Antarctic populations colonized the New Zealand mainland within the last few hundred years, following the extinction of a newly described sister species, Megadyptes waitaha, due to hunting by early Polynesian settlers. M. waitaha is genetically and morphologically different from sub-Antarctic fossil specimens and modern M. antipodes.
Distributed along the southeast coast of New Zealand, the sub-Antarctic Campbell and Auckland Islands, and Foveaux Strait, including: Stewart and Codfish Islands. The largest concentration of Yellow-Eyed Penguins occurs on the Otago Peninsula, on the New Zealand mainland.
Migration patterns: Adults remain at or near their breeding grounds year round. Juveniles will migrate as far as the Cook Strait in their first year after fledging.12, 18
BREEDING BIOLOGY4, 7, 9, 14, 18
From various colonies on Otago Peninsula, the same general patterns are observed throughout the entire range.
Average arrival date: Mid August
Nest and nest materials: Nests are built against a solid structure such as a tree or rock and are composed of sticks, twigs, and grasses.
Nest density: 1-5 per hectare. 12-32 meters apart depending on vegetation type.
Egg laying average date: September 30
Incubation: 35-54 days
Egg weight: 111-158 g
Egg length: 7.69-7.70 cm
Egg breadth: 5.74-5.76 cm
Egg laying intervals and dimorphism: Eggs are laid 3-5 days apart, but hatch synchronously. Both eggs are of similar size.
Laying eggs again: one clutch of eggs per season
Chick period: 40-50 days
Fledgling period: approximately day 106, late February-mid March
Average weight at fledging: 5.66 kg
Reproductive success on Otago Peninsula: An average of 1.0 chicks/nest. First time breeders tend to have decreased reproductive success.
Chick crèches: Typically, chicks do not form crèches. However, occasionally small crèches (3-7 chicks) are observed on Campbell Island due to lower nest densities.
Age at first breeding: 2-3 years
Max lifespan: 22 years
Average lifespan: 20 years
Molt: Typically molt begins about 22 days after chick fledging, late February to late March. After chicks fledge, the adults will put on about 2-3 kg of weight in preparation of molt. Molt lasts for about 3-4 weeks. Yellow-Eyed Penguins molt only once per year, and thus molt all of their feathers at once. Because of this, they are unable to forage at sea for food and will lose about 3-4kg in weight.
Description of general breeding patterns: Yellow-Eyed Penguins form monogamous pair bonds that may last for several breeding seasons. They also exhibit high site fidelity, returning to the same breeding colonies consistently year after year. A large percentage of pairs remain together for 2-6 seasons. From studies on Otago peninsula, some individuals may skip one or two consecutive breeding seasons due to the loss of a mate.
PREDATORS AND PREY
PREY8, 12, 18
Benthic species such as Arrow Squid (Nototodarus sloaniii), Red Cod (Pseudophycis bachus), Blue Cod (Parapercis colias), Sliversides (Menidia menidia), Opal fish (Hemerocoetes monopteryguis), Sprat (Spratus antipodium), and Aruhu (Auchenoceros punctatus).
Yellow-Eyed Penguins primarily feed on benthic species due to more predictability of food availability in these areas than pelagic species which can vary seasonally due to variations in currents and sea surface temperatures. The Blue cod (Parapercis colias) is primarily found closer to shore but is of little nutritional value and thus composes a lower proportion of their diet. Other benthic species that are higher in nutritional value are found in further offshore waters.
PREDATORS2, 5 , 6, 14, 18
Introduced predators on land include stoats (Mustelia erminea), ferrets (Mustelia furo), cats and dogs, all which prey upon adults, juveniles and chicks. Rats (Rattus spp.), wekas (Gallirallus australis), and bushtail possums (Trichosurus vulpecula) also prey upon eggs and chicks.
At sea, Hooker’s Sea Lions (Phocarctos hookeri), barracouta (Thyrsites atun), and various shark species prey upon adults, juveniles and fledglings.
Unnatural predators are being introduced by humans (e.g. cats, dogs, stoats, and ferrets) and Hooker’s Sea Lions (Phocarctos hookeri), which are also a threatened species, have begun attacking Yellow-Eyed Penguins at a greater rate. Although attacks are currently being carried out by a few individual female sea lions, whom are significant breeders within the sea lion population, any increase in attacks may not be sustainable for penguin populations to withstand. Also, the fact that both of these species are threatened presents a conservation dilemma.