Kakapo are herbivores whose diet spans an impressive range of native New Zealand plants, from the leaves and roots of forest-floor ferns to the fruits of towering podocarp trees. The single most important food item in their modern diet is the fruit of the rimu tree, which plays a pivotal role in triggering breeding. But the story of what kakapo eat is also a story of what they have lost: analysis of ancient droppings shows that their historical menu was far broader than what survives today, and conservationists trying to fill the gaps with supplementary food have run into unexpected biological complications.
A Plant-Based Menu with Seasonal Shifts
Kakapo are among the few parrots that eat an entirely plant-based diet. They graze on leaves, chew fibrous stems, strip bark, eat roots, and consume fruits and seeds across dozens of native species. Microscopic analysis of 52 kakapo coprolites (fossilized droppings) identified material from roughly 30 different plant groups, including podocarps, broadleaf trees, shrubs, grasses, ferns, mosses, and liverworts.1Review of Palaeobotany and Palynology. Plant microfossil analysis of coprolites of the critically endangered kakapo (Strigops habroptilus) parrot from New Zealand That study described kakapo as “versatile feeders, using a broad spectrum of foods that may only be available for short periods and intermittent years.” In practice, this means a kakapo’s diet shifts with the seasons. During leaner months, the birds rely more on leaves, roots, and rhizomes. When fruiting seasons arrive, they switch to energy-rich fruits and seeds.
Kakapo have a distinctive way of processing tough plant material. Rather than swallowing leaves whole, they often chew vegetation thoroughly, extracting the juice and nutrients while leaving behind compressed wads of fiber called “chew marks.” These discarded fiber bundles, found littering the ground beneath favored feeding trees, are one of the telltale signs researchers use to track where kakapo have been feeding. The birds also use their strong beaks to strip bark and dig up roots and rhizomes, particularly from ferns.
Rimu Fruit and the Breeding Connection
No food item matters more to kakapo reproduction than the fruit of the rimu tree (Dacrydium cupressinum), a native podocarp that dominates many lowland New Zealand forests. Kakapo breed almost exclusively in years when rimu trees produce abundant fruit, a pattern called masting. The relationship is so tight that conservation managers monitor rimu fruiting to predict when breeding seasons will occur. Research has confirmed that abundant rimu fruit in a given year is linked to whether kakapo breed at all, though it does not appear to affect clutch size.2Biological Conservation. The use of a nutritional supplement to improve egg production in the endangered kakapo At the time females actually lay their eggs, rimu fruit is still small and unripe, so the developing fruit likely serves as a signal that enough food will be available for rearing chicks later in the season, rather than a direct energy source for egg production.
What makes rimu fruit such a valuable breeding food goes beyond calories. Nutrient analysis found that rimu berries are unusually rich in calcium, at about 8.4 milligrams per gram of dry matter, which is critical for both eggshell formation and the growing skeleton of chicks. The berries also contain high levels of vitamin D2 and moderate levels of vitamin D3, making them what researchers described as potentially “the perfect food package for breeding and nesting birds.”3PubMed. Preferred natural food of breeding Kakapo is a high value source of calcium and vitamin D Vitamin D aids calcium absorption, so a food that delivers both nutrients simultaneously is especially useful during the physically demanding breeding period. This nutritional profile helps explain why kakapo have evolved such a deep dependence on rimu masting cycles, even though it means they may go several years between breeding attempts.
A Diet That Has Shrunk Over Centuries
Modern kakapo survive only on a handful of predator-free offshore islands where they were relocated by conservationists. These islands support a narrower range of vegetation than the vast mainland forests kakapo once inhabited, and the dietary consequences are dramatic. A large-scale metabarcoding study comparing over 100 ancient coprolites (dating from roughly 400 to 1900 AD) with over 100 modern frozen scats found that the historical diet included 24 plant orders, 56 families, and 67 native genera that do not appear in modern kakapo diets, representing increases of roughly 69%, 108%, and 75% respectively over what is recorded today.4Frontiers in Ecology and Evolution. Ancient and modern scats record broken ecological interactions and a decline in dietary breadth of the critically endangered kākāpō parrot (Strigops habroptilus)
Some of the most striking losses involve canopy-forming trees and parasitic plants. Southern beeches, which are major forest trees across much of New Zealand’s upland terrain, dominated kakapo diets at higher elevations historically but are not an important food today. Kakapo also frequently consumed hemiparasitic mistletoes and a remarkable plant called the wood rose (Dactylanthus taylorii), a root parasite that grows entirely underground except for its flowers. These plants are nutrient-rich, but their populations have been hammered by introduced mammals that browse the host plants and destroy the parasites themselves. The ranges of kakapo and Dactylanthus no longer overlap at all, but coprolite analysis found Dactylanthus pollen making up a notable proportion of the plant material in ancient kakapo droppings, supporting the idea that kakapo once fed directly on the plant’s flowers.5PubMed. A lost link between a flightless parrot and a parasitic plant and the potential role of coprolites in conservation paleobiology Today, the only known native pollinator of Dactylanthus is the lesser short-tailed bat, but the coprolite evidence raises the possibility that kakapo once played a role in pollinating or dispersing this threatened plant.
Fungi on the Menu
Plants are not the only thing kakapo have eaten. Analysis of prehistoric coprolites revealed that kakapo consumed ectomycorrhizal fungi, the kinds of fungi that form symbiotic relationships with tree roots and are essential to the health of New Zealand’s native forests.6PubMed Central. Coprolites reveal ecological interactions lost with the extinction of New Zealand birds This is significant because many of these fungi reproduce by producing underground fruiting bodies (similar to truffles) that depend on animals to dig them up and spread their spores. The same study found evidence of fungal consumption in the coprolites of extinct moa, suggesting that before human settlement, multiple large bird species helped maintain fungal diversity in New Zealand soils. With moa gone and kakapo confined to small islands, this fungal dispersal role has effectively been lost from the mainland ecosystem.
Whether modern kakapo on their island sanctuaries still eat fungi is less clear, but the historical evidence suggests that mycophagy (fungus-eating) was a routine part of their diet when they had access to extensive forest floors. For a ground-dwelling bird that spends its nights shuffling through leaf litter, encountering underground fungal fruiting bodies would have been a natural foraging opportunity.
How Kakapo Find Their Food
Kakapo are nocturnal, and their foraging strategy relies heavily on smell. Unlike most parrots, which are active during the day and find food largely by sight, kakapo have evolved a substantially expanded repertoire of olfactory receptor genes. Research comparing the olfactory genetics of kakapo and brown kiwi (both nocturnal, ground-dwelling New Zealand birds) with their closest day-active relatives found evidence that both nocturnal species have larger olfactory receptor gene repertoires than their relatives.7PubMed Central. Evidence for increased olfactory receptor gene repertoire size in two nocturnal bird species with well-developed olfactory ability For kakapo, the comparison was with kea and kaka, two closely related New Zealand parrots that are active during the day and forage by sight.
A strong sense of smell makes practical sense for a bird foraging in a dark forest at night. Ripe fruits, flowers, fungi, and even nutritious roots all produce volatile chemical compounds that a sensitive nose can detect. Kakapo are also known to have a distinctive musty, sweet odor themselves, which unfortunately made them easy for introduced mammalian predators like cats and stoats to track. The same olfactory sensitivity that helps kakapo find food in the dark is thought to play a role in social communication between individuals.
Digesting a Fibrous Diet
Eating large quantities of leaves, stems, and fibrous plant material is challenging for any bird, and kakapo have evolved some unusual digestive features to cope. They are known to chew food more thoroughly than most parrots, which helps break down tough cell walls before swallowing. But the real work of digestion depends partly on the community of microbes living in the gut.
Studies of the kakapo gut microbiome have found that it is relatively simple compared to those of many other herbivorous animals. Analysis of bacterial diversity across several birds revealed a community dominated by just two major bacterial groups: Firmicutes (which include lactic acid bacteria) and Gammaproteobacteria.8PubMed Central. Gut microbiome of the critically endangered New Zealand parrot, the kakapo (Strigops habroptilus) That is a low level of diversity by the standards of most herbivores. A follow-up genomic study of the microbiome found that while certain bacteria (members of the Enterobacteriaceae family) are capable of beginning the process of breaking down cellulose, none of the bacterial strains present appeared to be cellulose-digesting specialists. Other bacterial lineages could metabolize the byproducts of initial cellulose breakdown but could not tackle long-chain cellulose on their own.9Scientific Reports. Network-guided genomic and metagenomic analysis of the faecal microbiota of the critically endangered kakapo
This limited cellulose-digesting ability may help explain why kakapo chew so thoroughly and why they are selective about which plant parts they eat. Rather than gulping down large amounts of raw leaf material and relying on gut fermentation (as a cow or a horse would), kakapo seem to extract nutrients mechanically through intense chewing and then depend on their gut bacteria to finish the job on smaller, partially broken-down plant fragments. It is an approach that works, but it probably limits how much energy kakapo can extract from any given meal.
The Lowest Energy Budget of Any Wild Bird
Kakapo have solved the efficiency problem not by digesting more but by needing less. Measurements of free-living kakapo found that their daily energy expenditure averaged about 799 kilojoules per day, equivalent to roughly 1.4 times their basal metabolic rate. That is the lowest daily energy expenditure recorded for any adult wild bird.10Notornis. Energetics of free-living kakapo (Strigops habroptilus) For context, most wild birds burn energy at two to three times their basal rate during a normal day. Kakapo barely exceed their resting metabolism.
This extremely low energy budget is consistent with the kakapo’s entire lifestyle: flightless, nocturnal, slow-moving, and solitary for much of the year. Flight is the single biggest energy cost for most birds, and kakapo have eliminated it entirely. Their low metabolic needs mean they can survive on a diet that would leave a flying parrot of similar size malnourished. It also means they can afford to wait out years when food is scarce, breeding only when rimu masting years deliver a surplus. The downside is that this metabolic thriftiness contributes to their tendency to accumulate fat readily, which becomes relevant when conservationists provide supplementary food.
Supplementary Feeding and Its Unintended Consequences
With fewer than 250 kakapo alive, every breeding attempt matters enormously. Conservation managers began providing supplementary food to wild kakapo in 1989, hoping to encourage nesting more frequently than natural rimu masting cycles would allow. The supplementary diet initially included apples, sweet potato (kumara), and the kernels of almonds, brazil nuts, sunflower seeds, and walnuts, supplied each night at feeding stations.11Biological Conservation. Use of supplementary feeding to induce breeding in free-living kakapo Strigops habroptilus in New Zealand Females did nest at the feeding sites, but nesting success was low in those early years.
A more serious problem emerged as data accumulated: supplementary feeding was skewing the sex ratio of chicks heavily toward males. Because kakapo are polygynous (males compete for mates, and larger males tend to be more successful), evolutionary theory predicts that well-fed females in good body condition will produce more sons, since a large, healthy son has a higher reproductive payoff than a large daughter. That is exactly what happened. Females receiving supplementary food produced significantly more male offspring.12Biological Conservation. Effects of supplementary feeding on the offspring sex ratio of kakapo: a dilemma for the conservation of a polygynous parrot For a species where every female is precious and the population is tiny, an excess of males is a serious setback.
Researchers confirmed the pattern and demonstrated that adjusting maternal condition through changes in feeding could shift chick sex ratios back toward balance.13PubMed Central. Sex allocation theory aids species conservation The modern kakapo recovery program now carefully calibrates supplementary feeding to encourage breeding without pushing females into such high body condition that they overproduce males. It is a delicate balancing act that illustrates how deeply diet connects to every aspect of kakapo biology, from individual health to population-level demographics.
Lost Ecological Roles
When kakapo ate more broadly across mainland New Zealand, they were not just consumers. They were participants in ecological networks that have since unraveled. Their consumption of mistletoe fruits and wood rose flowers made them likely dispersers and pollinators of plants that are now critically threatened. Their habit of eating underground fungi would have spread fungal spores across the forest floor, maintaining the mycorrhizal networks that help trees absorb water and nutrients. Even their grazing on fern rhizomes and moss would have influenced the structure of the understory.
The coprolite evidence for a former kakapo-Dactylanthus feeding relationship is a good example of how dietary studies can reveal conservation opportunities. If kakapo once helped pollinate this plant, then restoring kakapo to mainland sites where Dactylanthus still grows could theoretically benefit both species. For now, the sole confirmed pollinator remains the short-tailed bat, but the historical record suggests the ecological web was once more interconnected than it appears today.5PubMed. A lost link between a flightless parrot and a parasitic plant and the potential role of coprolites in conservation paleobiology Similarly, the dramatic decline in dietary breadth documented by the comparison of ancient and modern scats is not just an academic curiosity. It quantifies how much ecological function has been lost when a species is confined to a few small islands with limited vegetation diversity.4Frontiers in Ecology and Evolution. Ancient and modern scats record broken ecological interactions and a decline in dietary breadth of the critically endangered kākāpō parrot (Strigops habroptilus) Understanding what kakapo once ate is not just about the birds themselves; it is a window into what New Zealand’s forests have lost.