The Roles of Soil Characteristics and Toxin Adsorption in Avian Geophagy

Abstract

Geophagy, the intentional ingestion of soil, is a widespread phenomenon whose function is still debated. Recent studies suggest that consumed soils adsorb dietary toxins and provide sodium. However, quantification of soil choice has been absent from most studies, prohibiting the direct comparison of soil use and characteristics.To determine correlates among bird use and soil characteristics, we analyze physical structure, mineral composition, and alkaloid adsorption (14 soil characteristics in total) for 22 soil samples from a riverbank 'clay lick' used by macaws and parrots (family Psittacidae) in Amazon lowland forests in the Tambopata region of southeastern Peru. We quantified bird preferences through photographic mapping. Mineral concentrations were determined using analyses designed to approximate the mineral availability in the vertebrate stomach. The sodium levels in the soil were much higher than in food plants consumed by parrots in this region. Both adsorption of quinine, the model alkaloid used, and sodium concentration correlated significantly with bird use. Sodium explained a much higher percentage of the variation in bird use than quinine adsorption. However, the analyses were complicated by the high degree of correlation among soil variables: clay percentage and sodium concentration were highly correlated with each other and with bird use, making it impossible to determine which of these may have the greater contribution to bird preference. The results suggest that the soils consumed provide an important source of dietary sodium and adsorb alkaloid toxins.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.

Nutrients Drive Termite Nest Geophagy in Yellow-chevroned Parakeets (Brotogeris chiriri)

“…Apart from providing a safe site for nesting, the consumption of arboreal termitaria during nest excavation may supply nutrients with important physiological functions and bind toxins present on fruits consumed by B. chiriri. Further studies comparing nutrient levels in food resources versus feces versus soil, and quantifying sodium content in termite versus ground soil may help clarify the physiological advantages of termite soil consumption by B. chiriri (see Brightsmith et al 2008Brightsmith et al , 2010Dudley 2012).…”

“…All these nutrients are associated with physiological functions in vertebrates (Marshall and Hughes 1980). Unfortunately, we could not carry out a sodium content analysis due to logistical constraints, which has been suggested as one of the main drivers of geophagy in vertebrates (Brightsmith et al 2008, Powell et al 2009, Dudley et al 2012.…”

“…Most of these hypotheses remain insufficiently tested, and many studies focus on observational studies of geophagy (Wilson 2003). Field studies that combine behavioral observations with ecological and chemical analysis have provided evidence that mineral supplementation and adsorption of dietary toxins are the main drivers of geophagy in natural populations of vertebrates , Brightsmith and Muñoz-Najar 2004, Brightsmith et al 2008). …”

Geophagy in Brown Spider Monkeys (Ateles hybridus) in a Lowland Tropical Rainforest in Colombia

“…and one species of howler monkeys (Alouatta seniculus) are regular visitors at mineral licks [Ferrari et al, 2008]. Several non-exclusive hypotheses have been proposed to explain the functionality of geophagy in mammals and birds [Johns and Duquette, 1991;Krishnamani and Mahaney, 2000;Brightsmith and Muñoz-Najar, 2004;Brightsmith et al, 2008]. The most accepted hypotheses propose that soil (1) can help detoxify secondary plant metabolites and tannins [Gilardi et al, 1999;Johns and Duquette, 1991], (2) can provide supplementary minerals that might be absent or in very low concentration in an animal's diet [Oates, 1978;Brightsmith et al, 2008;Lee et al, 2009], (3) can act as an anti-diarrhoeal drug [Krishnamani and Mahaney, 2000] or (4) can be associated with the enhancement of the pharmacological properties of secondary plant compounds [Klein et al, 2008].…”

“…Several non-exclusive hypotheses have been proposed to explain the functionality of geophagy in mammals and birds [Johns and Duquette, 1991;Krishnamani and Mahaney, 2000;Brightsmith and Muñoz-Najar, 2004;Brightsmith et al, 2008]. The most accepted hypotheses propose that soil (1) can help detoxify secondary plant metabolites and tannins [Gilardi et al, 1999;Johns and Duquette, 1991], (2) can provide supplementary minerals that might be absent or in very low concentration in an animal's diet [Oates, 1978;Brightsmith et al, 2008;Lee et al, 2009], (3) can act as an anti-diarrhoeal drug [Krishnamani and Mahaney, 2000] or (4) can be associated with the enhancement of the pharmacological properties of secondary plant compounds [Klein et al, 2008]. The higher concentration of minerals such as calcium, sodium or potassium, amongst others, from the mineral lick soils when compared to control sites [Emmons and Starck, 1979;Izawa, 1993;Montenegro, 2004;Mahaney et al, 2005], combined with the frequent use of mineral licks by many bird and mammal species, suggests that it has beneficial effects on their nutrition and health.…”