A dietary check-up for parrots in the western Amazon

Posted by Alan Lee

In a recently published paper, Alan, Stu and others report on an intensive study of the diets of a range of parrots in Peru. Dietary data of this sort are rare – seldom are the resources/person-power available to accumulate the data, and studying diets is not always seen as a fashionable way to go about ecology. Here, Alan talks about the study, its making, and its findings.

Parrots have good manners – they don't tend to speak with their mouths full. That makes them a bit hard to find when foraging quietly in the upper canopy. Luckily, they are messy eaters, and fruit fall invariably leads the observer to something frugivorous, be it a Red-howler monkey (Alouatta seniculus), Spix's Guan (Penelope jacquacu), Curl-crested Aracari (Pteroglossus beauharnaesii) or one of the 20 odd species of parrot – if you happen to be looking for them in the lowland Amazon rainforests of Peru. Together with people from all walks of life, I registered birds eating food for over two years, amassing a data set of over 1500 encounters with foraging parrots. 

Aldo, Philip, and Percy test what the macaws have been eating (Photo A. Lee)

One of the first things we noticed was that these birds prefer to forage from the same individual trees – usually amongst the largest tree (adults, and at least at canopy level). For the sake of independent samples, many of these repeat encounters needed to be omitted – but they accounted for over 10% of all encounters. We would place foraging tape on trees marked when a foraging encounter had been recorded, and soon some of the more frequently walked trails were decorated with registrations. 

A foraging event, the left over breakfast: macaws cracked open and at the seeds from this noxious vine (Photo A. Lee)

To account for the fact that we may be missing birds foraging on smaller items, like small fruit and flowers, we also watched birds from canopy towers, as well as when floating down the river by boat to town from our study sites along the Tambopata River. Rather unsurprisingly given the difference in sizes of the parrots involved, we found that different parrots fed on different plant species and reproductive parts. For example, while all parrots fed on Brazil nut trees, large macaws with their powerful beaks went for the developing seed pods, while the smaller parrots fed on the flowers. All parrots loved the fruits and seeds of the Wasai palm.

While the colourful or endangered macaws
are most frequently photographed at
claylicks, its the little and common
Dusky-headed parakeets that
visit in greatest numbers.
(Photo A. Lee)

One of the main reasons we were recording foraging events was to document what plant parts were being consumed (e.g. fruit pulp or seeds) and whether the fruit were ripe or unripe. We were expecting that our records of surveys of the geophagy sites in the area (claylicks where birds would eat soil) should indicate those birds that eat more seeds and unripe food items should be those that eat more soil, if the theory held that the clay binds dietary toxins. This is because unripe fruit and seeds tend to have higher quantities of tannins and other things that make the unripe fruit taste unpleasant – at least to us. This is because the plants don't want to have their reproductive bits eaten after all.

Red-and-Green Macaws at a claylick
on the Los Amigos River (Photo A. Lee)

In addition to the fun task of watching parrots feasting, we also undertook the more onerous task of recording the fruiting status of 1800 individually marked trees every month. We did this to understand phenology patterns – to identify if there were any periods with little food availability that could perhaps drive the parrots to consume soil in the absence of food. Although there was a clear pattern of peak flowering and fruiting seasons, there was something fruiting of flowering throughout the year, especially if we concentrated only on the plant species the parrots preferred to forage on. So there is no evidence that these parrots eat soil due to bottlenecks in food availability.









We had previously worked out bird densities for the region by conducting line transects at multiple sites in the area (http://onlinelibrary.wiley.com/doi/10.1111/j.1744-7429.2011.00847.x/abstract), so we could calculate an estimate for the population of birds that were in the vicinity of a claylick i.e. the audience. What we found when we divided upper estimates of the numbers of birds feeding on the clay by the local population, was that the macaws – the parrots most famous for eating seeds and unripe fruit items – in fact did not consume more clay than expected. Surprisingly, it was the parakeets associated with secondary forests – Dusky-headed (Aratinga weddellii) and White-eyed parakeets (Psittacara leucophthalma) – that were represented on the claylicks more than expected. 

In the popular literature claylicks are associated with, and illustrated by, the large and colorful members of the parrot family - the macaws (Photo A. Lee)

Furthermore, our foraging encounters also suggested that these birds ate more flowers – specifically balsa flowers (Ochroma pyramidale) – than seeds. In addition, those species that were associated with terra-firme forests (White-bellied parrots Pionites leucogaster and Orange-cheeked parrots Pyrilia barrabandi) were observed less frequently on claylicks. 
Most publications investigating patterns of clay consumption or reasons for clay consumption from the Peruvian Amazon have concluded that they do it for the sodium. Our dietary study at least does not support the alternative hypothesis – that they do it to counter dietary toxins. 

The research has been funded by: