Saturday, 1 February 2014

Dishing the dirt on Peru’s parrots

Posted by Alan Lee and Stuart Marsden

Alan Lee finished his PhD in the group three years ago. His PhD, supervised by Stu, along with Martin Jones (MMU), and Donald Brightsmith of Texas A&M University, focused on the ecology of the rich parrot community of southeastern Peru, and in particular examined how and why the various species consume clay at colpas (claylicks). Geophagy is the intentional consumption of ‘dirt’ – something which a surprising variety of animals do. Chimpanzees and a range of new world monkeys have been recorded eating dirt (often from termitaria). Herbivorous mammals such as tapir, peccary, deer, agoutis and bats have been recorded drinking salty water and eating dirt at claylicks in South America, while several publications have examined geophagy in elephants in Africa and Asia. Markets in West Africa sell small bags of special clay for pregnant women. 


Red-and-green Macaws at the Blanquillo claylick in Manu

Geophagy and consumption of mineral-rich water is common in the tropics especially among frugivorous birds such as parrots and pigeons. This said, we still do not know how common and widespread geophagy is in birds – largely because it is difficult to observe in the vast and little-known tropical forests. Previous work by Dr Craig Symes, another South African who worked in our group, recorded fourteen pigeon species and six parrot species practising geophagy, or drinking salt water in a forest in Papua New Guinea (61% of the sites parrots and 30% of parrots). Cassowary was recorded eating blue soil rich in iron and the conclusion from this study is that different birds in the area were using different dirt for different reasons (Symes et al. 2006).

Alan and Red-tailed Boa Constrictor




Before his PhD, Alan had spent a couple of years working for an NGO ostensibly to investigate the impacts of tourism on Amazonian wildlife, and volunteered on the Tambopata Macaw Project under Donald Brightsmith. He learnt a lot about the wildlife of the region but was most fascinated by the geophagy sites along the rivers of SE Peru, where parrots would flock together in the early morning, fly around noisily, look spectacularly beautiful and then some of them would descend to the river banks to munch on soil. But not always, and not evenly, and not everywhere. It was Alan’s task to figure out if there was a pattern to this spectacle – a spectacle so impressive that several successful tourist enterprises had been built on the back of this raucous feathered firework show. 

 








Together with a handful of volunteers from all walks of life, we spent hundreds of hours at many parrot geophagy sites across the Peruvian Amazon. We braved jaguars, herds of peccary, floods, rabid bats, terrorist attacks, flesh eating diseases, and a host of other difficulties to try and understand parrots and their ways. The first job was to map out across the entire continent where the claylicks were found, and to use MaxEnt, a presence-only species (or in this case, claylick) distribution model to determine where claylicks were and perhaps why they were in some areas and not others. We realised that they were only found in the western sections of the Amazon, where sodium deficits are the greatest (Lee et al. 2010).



The next job was to put the numbers of parrots which regularly use the region’s riverbank claylicks into perspective of the numbers of parrots in the areas – do all parrots visit claylicks everyday? We made many counts of parrots at various claylicks but a more difficult job was trying to survey parrots in the tall and complex Amazonian forest. This problem led us to propose a variant of Distance Sampling based on call counts which may be a useful line transect method in tall forests (Lee & Marsden 2012). In respect to geophagy, our results suggested that only a small proportion of the parrots in the area visit claylicks on a given day – the consumption of clay seems to be more of a ‘topping up’ habit than a daily necessity.



This is important in terms of our understanding of why parrots eat dirt. While several researchers have posited that the soil was being consumed for the sodium contained therein, a PhD conducted by Jamie Gilardi during the nineties had convinced much of the world that the soil was consumed in order to neutralise the natural toxins found in the seeds and unripe fruit. This is a fascinating possibility – Jared Diamond and team in a publication on geophagy and birds from Papua New Guinea highlighted the behaviour in the light of the toxin-arms race between plants and parrots who predate rather than disperse their seeds (Diamond et al. 1999). 

Dusky-headed Parakeets and Blue-headed Macaws

That claylicks are concentrated in a small portion of South America where sodium deficits are likely to be highest, and that parrots tend to visit claylicks periodically and not continuously may suggest that the reason for parrot geophagy is mineral- rather than toxin-related. A final strand of enquiry, which we are about to publish, looked at the diets of different parrot species and their tendency to visit claylicks. Again, we were unable to link geophagy to toxin neutralization - in fact, it was flower-eating successional-forest parrot species that seemed to consume more soil than those large macaws that predate more toxin-rich seeds and unripe fruit. We will detail these findings in an upcoming post.


Alan now has a postdoctoral research position at the University of Cape Town investigating how the endemic birds of South Africa's endemic biome (the Fynbos) will fare under climate change scenarios. The work is almost as exciting as it was in the Amazon – you can read all about it at http://bluehillescape.blogspot.com/

Alan's PhD research was done in association with the Tambopata Macaw Project

 macaw logo


References


Diamond, J., Bishop, K.D. & Gilardi, J.D. (1999). Geophagy in New Guinea birds. Ibis 141: 181-193.


Lee, A.T., Kumar, S., Brightsmith, D. & Marsden, S.J. (2010) Distribution of claylicks and their use by parrots across South America: Do patterns of where help answer the question why? Ecography 33: 503-513.


Lee, A.K.T. & Marden, S.J. (2012). The influence of habitat, season and detectability on abundance estimates across an Amazonian parrot assemblage. Biotropica 44: 537-544.


Symes, C. T., Hughes, J. C., Mack, A. L. & Marsden, S. J. (2006). Avian geophagy in the Crater Mountain Wildlife Management Area, Papua New Guinea. Journal of Zoology 268: 87-96.

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