Better even than Amazon, the blue macaws are a rapid and highly mobile airmail distribution service — for palm seeds

A few months ago, I shared a study about parrots’ wasteful eating habits, which found that approximately half of the foods they handled ended up on the floor (more here). Wasting food doesn’t make much sense, especially in the wild, which raises the question: are there any practical effects of slobby eating?

A new study may provide some clues. A team of researchers studying the two all-blue macaw species has found that these parrots help spread the seeds of 18 plant species in Brazil and Bolivia (ref). They came to this conclusion by direct observations and camera traps that recorded more than 1,700 fruit and nut dispersal events by hyacinth and Lear’s macaws. Both species were found to be effective seed dispersers, despite suspicions that these parrots fully consume all seeds in the fruits or nuts they picked. This finding challenges previously held ideas that the dispersal of large seeds in South America was carried out by now-extinct Pleistocene megafauna.

There are two large all-blue macaw species alive in the wild today: the hyacinth macaw, Anodorhynchus hyacinthinus, and Lear’s macaw, Anodorhynchus leari. With a wingspan of one meter (3.3 feet), the hyacinth macaw is the largest of all the macaws, and is the largest parrot in the world. The hyacinth macaw has bright yellow skin patches around its eyes and a distinctive yellow patch at the base of its massive black beak. It is found in several discrete areas in central and eastern South America (Figure 1), and is classified as Vulnerable due to poaching for the wild bird trade (more here).

Lears macaw, also known as the indigo macaw, is slightly smaller than its darker blue cousin, and is sometimes mistaken for it. But Lear’s macaws can be distinguished from hyacinth macaws by its own specially shaped yellow skin patch at the base of its large black beak, and by the faint greenish tinge to its paler blue plumage. Rediscovered in 1978, Lear’s macaw is rare within its extremely restricted ranges in eastern Brazil (Figure 1) and is Endangered because of poaching for the illegal wild bird trade.

The two surviving Anodorhynchus macaw species have the strongest beaks amongst the parrots, capable of easily breaking open even the largest and strongest nuts produced by a variety of palm trees (ref). But are these parrots consuming all of the seeds or are they behaving as other parrots do by dropping a fair number of undamaged seeds throughout the landscape?

To better understand these two parrots’ relationships with the seeds they eat, an international team of researchers carried out dozens of expeditions and placed 35 infrared-triggered camera traps in the Caatinga, Cerrado and Pantanal biomes in Brazil and Bolivia. Whilst there, they recorded 1,722 seed dispersal events (1590 through direct observations and 132 through camera trapping), and observed the macaws flying with nuts for up to 1.6 kilometers (1 mile) from where they picked them (Figure 2).

In this study, researchers recorded that both macaw species defleshed palm fruits after picking them from the mother plant (figure 2a) and before transporting the nut to a distant perching site where it was broken open and the seeds consumed (Figure 2b,c). Nuts were mainly dispersed by carrying in a flying parrot’s bill but were sometimes carried in its feet (Figure 2d).

Most of the fruits dispersed (97.7%) were from six palm species, and almost all, if not all of them, could be considered as dependent upon megafauna for seed dispersal. In most cases, the researchers observed primary seed dispersal events (92.6%), where the macaw picked the fruit from the mother plant and moved it to another location. However, the researchers did record 121 instances of tertiary seed dispersal, where the macaws collected palm seeds that had been regurgitated by cattle and goats (Figure 2g,h). Nearly all of these (96.7%) tertiary seed dispersal events applied to just one palm species, Acrocomia totai.

After the macaws had flown away with a palm fruit, the researchers located the perches where the macaws handled and consumed the fruits and searched for both damaged and undamaged seeds to compare the proportion of those that survived (Figure 3e), and also looked for germinating seeds and sapling palms.

Seed dispersal distances varied between species

Dispersal distances varied greatly between the two Anodorhynchus macaws. Primary dispersal distances for hyacinth macaws ranged from 1-1620 meters (Figure 4a) and from 3-1000+ meters for Lear’s macaws (Figure 4b).

Additionally, dispersal distances varied between the five main palm species, too, and curiously, these distances were unrelated to fruit size.

Anodorhynchus macaws and palms evolved together

The dependence of the Anodorhynchus macaws on the seeds of palms as well as their role as dispersers of their seeds suggests this led to an evolutionary arms race between the parrots and the palms. Specifically, the palms evolved an extremely hard coat around its fruits to avoid seed predation by the macaws. The macaws evolved ever-larger and more powerful beaks to crack the palms strong nut coats so they could consume the seeds contained within. The result of this arms race may have been exploited by the palms to exclude all seed predators except the Anodorhynchus macaws, thereby ensuring that some of their seeds were dispersed over long distances by these strong and highly mobile flyers.

The evolutionary relationship between the Anodorhynchus macaws and their palms is apparently an ancient one. Multiple molecular studies have identified when parrots first originated and have found many of their lineages began speciating rapidly around 66 million years ago (i.e., ref). This coincides with an important time in palm evolution, too, where there was extensive speciation and changes in the traits of their fruits, both of which could have resulted from coevolution with parrots. In contrast, extinct mammalian megafauna arose much later than both the parrots and the palms whose seeds they presumably dispersed.

This study argues that the Anodorhynchus macaws perform an important long-distance air-delivery service that large-fruited palms rely upon to maintain gene flow between isolated groups and to regenerate palm stands. In view of the severe range contractions and extinctions that the Anodorhynchus macaw species suffered, their mutually beneficial interactions with a variety of palm species have surely disappeared from large portions of their former ranges. This recent history could be the cause of currently observed spatial and genetic arrangements of palm seedlings versus adult plants (ref).

Local and global extinctions of the Anodorhynchus macaws could provide important test cases for gaining a better understanding of the effects of disruption of seed dispersal on palms. Currently, there is one reintroduction project for Lear’s macaw (ref), and this could be used for assessing the effects of recovery of ecological functions.

Anodorhynchus macaws are globally threatened species

Both of the Anodorhynchus macaws have suffered dramatic population decreases in recent decades as well as reductions in their geographic ranges and thus, are classified as threatened by the IUCN Red List. The hyacinth macaw has a total estimated population of just 6500 individuals, distributed between three regions of the Pantanal, Cerrado, and Amazonia (Figure 1), probably with no genetic flow between them (ref).

Lear’s macaw has experienced an even more severe range contraction. Originally distributed throughout the Caatinga biome, which covers approximately 845,000 square kilometers (525,060 square miles), the entire world’s population of this species (estimated to number just 1200 individuals) is now concentrated into two breeding sites with a radius of around 50 km (30 miles) (ref) each (Figure 1).

These three biomes have been severely damaged by agriculture, cattle ranching and livestock overgrazing, which have markedly reduced the vegetation in the Cerrado and Pantanal biomes, and have contributed to the loss of Caatinga. These factors affect both macaw species but are especially worrying for Lears macaws because they prevent licuri palm stands (which produce 95% of the diet for Lear’s macaws) from regenerating.


José L. Tella, Fernando Hiraldo, Erica Pacífico, José A. Díaz-Luque, Francisco V. Dénes, Fernanda M. Fontoura, Neiva Guedes and Guillermo Blanco (2020). Conserving the Diversity of Ecological Interactions: The Role of Two Threatened Macaw Species as Legitimate Dispersers of “Megafaunal” Fruits, Diversity, 12(2):45 | doi:10.3390/d12020045