The rhea's diet mainly consists of broad-leaved foliage, particularly seed and fruit when in season, but also insects, scorpions, small rodents, reptiles, and small birds.

Favorite food plants include native and introduced species from all sorts of dicot families, such as Amaranthaceae, Asteraceae, Bignoniaceae, Brassicaceae, Fabaceae, Lamiaceae, Myrtaceae or Solanaceae.
Magnoliidae fruit, for example of Duguetia furfuracea (Annonaceae) or avocados (Persea americana, Lauraceae) can be seasonally important.

They do not usually eat cereal grains, or monocots in general.
However, the leaves of particular grass species like Brachiaria brizantha can be eaten in large quantities, and Liliaceae (e.g. the sarsaparilla Smilax brasiliensis) have also been recorded as foodplants.
Even tough and spiny vegetable matter like tubers or thistles is eaten with relish.

Like many birds which feed on tough plant matter, the greater rhea swallows pebbles which help grind down the food for easy digestion.
It is much attracted to sparkling objects and sometimes accidentally swallows metallic or glossy objects.

In fields and plantations of plants they do not like to eat, e.g., cereals or eucalyptus, the greater rhea can be a species quite beneficial to farmers.
It will eat any large invertebrate it can catch; its food includes locusts and grasshoppers, true bugs, cockroaches, and other pest insects.
Juveniles eat more animal matter than adults.
In mixed cerrado and agricultural land in Minas Gerais (Brazil), R. a. americana was noted to be particularly fond of beetles.
It is not clear whether this applies to the species in general but for example in pampas habitat, beetle consumption is probably lower simply due to availability while Orthoptera might be more important.

The greater rhea is able to eat Hymenoptera in quantity.
These insects contain among them many who can give painful stings, though the birds do not seem to mind.
Sometimes, greater rheas will gather at carrion to feed on flies; they are also known to eat dead or dying fish in the dry season, but as vertebrate prey in general not in large quantities.
The rhea's diet mainly consists of broad-leaved foliage, particularly seed and fruit when in season, but also insects, scorpions, small rodents, reptiles, and small birds. 
Favorite food plants include native and introduced species from all sorts of dicot families, such as Amaranthaceae, Asteraceae, Bignoniaceae, Brassicaceae, Fabaceae, Lamiaceae, Myrtaceae or Solanaceae. Magnoliidae fruit, for example of Duguetia furfuracea (Annonaceae) or avocados (Persea americana, Lauraceae) can be seasonally important.
They do not usually eat cereal grains, or monocots in general. However, the leaves of particular grass species like Brachiaria brizantha can be eaten in large quantities, and Liliaceae (e.g. the sarsaparilla Smilax brasiliensis) have also been recorded as foodplants. Even tough and spiny vegetable matter like tubers or thistles is eaten with relish.
Like many birds which feed on tough plant matter, the greater rhea swallows pebbles which help grind down the food for easy digestion. It is much attracted to sparkling objects and sometimes accidentally swallows metallic or glossy objects.
In fields and plantations of plants they do not like to eat, e.g., cereals or eucalyptus, the greater rhea can be a species quite beneficial to farmers. It will eat any large invertebrate it can catch; its food includes locusts and grasshoppers, true bugs, cockroaches, and other pest insects. Juveniles eat more animal matter than adults. In mixed cerrado and agricultural land in Minas Gerais (Brazil), R. a. americana was noted to be particularly fond of beetles. It is not clear whether this applies to the species in general but for example in pampas habitat, beetle consumption is probably lower simply due to availability while Orthoptera might be more important.
The greater rhea is able to eat Hymenoptera in quantity. These insects contain among them many who can give painful stings, though the birds do not seem to mind. Sometimes, greater rheas will gather at carrion to feed on flies; they are also known to eat dead or dying fish in the dry season, but as vertebrate prey in general not in large quantities.
Greater rhea