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Feeding ecology of Military Macaws (Ara militaris) in a semi-arid region of central Mexico.

Article Excerpt
Military Macaws (Ara militaris) occur in Mexico and northern South America (Forshaw 1989). In Mexico, the species is currently restricted to a few isolated populations in semi-deciduous and deciduous forests (Forshaw 1989, Carreon 1997, Collar 1997, Loza 1997), making occasional seasonal altitudinal movements to pine (Pinus spp.) and pine-oak (Quercus spp.) forests (Forshaw 1989, Peterson and Chaliff 1989, Collar and Juniper 1992, Howell and Webb 1995). The species is classified under Appendix I of the Convention on International Trade in Endangered Species (CITES 1998), and considered Vulnerable in the Red List of the International Union for the Conservation of Nature (SEMARNAT 2001, Birdlife International 2003). The species is considered in danger of extinction in Mexico, principally due to habitat loss and trade pressures (Inigo-Elias 2000).

Macaws are considered to have narrow diets using only between 10 and 23% of the available resources throughout the year (Carreon 1997, Loza 1997, Inigo-Elias 1999). Adult Scarlet Macaws (Ara macao), for example, used between 12 and 15 plant species in Belize (Renton 2006). The same species used 52 plant species in the Amazonian rainforest (Gilardi 1996), while in tropical dry forest in Peru they only used 28 species for food (Marineros and Vaughan 1995). Military Macaws in a semi-deciduous forest in western Mexico used six species for food that represented 10% of the available resources (Loza 1997).

A narrow diet makes populations vulnerable to changes in food resource availability associated with fragmentation and other forms of habitat loss, while a varied opportunistic diet can allow populations to adapt to habitat changes (Saunders 1977, Renton 2006). The objectives of our study were to describe: (1) the dietary composition of Military Macaws during the year, and (2) the nutritional composition of foods eaten.

METHODS

Study Area.--Field work was conducted at two sites in the Cuicatlan Basin in the State of Oaxaca, Mexico. The first was in Sabino Canyon (17[degrees] 51' 44.60" N, 97[degrees] 2' 43.89" W) where a colony of 70-90 Military Macaws roosts and nests in the vertical walls of the canyon (Salazar 2001, Rivera-Ortiz et al. 2008). The canyon occurs at 610-885 m asl and is dominated by tropical deciduous forest with columnar cacti (Valiente-Banuet et al. 2000). The mean annual rainfall is between 304 and 432 mm, and the mean annual temperature is 32[degrees]C. The rainy season occurs from June to September, and the dry season lasts up to 8 months (Rivera-Ortiz et al. 2008).

The second site was San Juan Coyula, between 17[degrees] 54' 47.45" N and 96[degrees] 55' 42.64" W with an elevation of 1,400-1,610 m asl. The main vegetation is oak forest (Valiente-Banuet et al. 2000). The mean annual temperature is between 16.9 and 18.7[degrees] C, and mean annual rainfall is 1,114 to 1,201 nun. The foothills of this area are dominated by tropical dry forest, which was also studied at el Aguacate, La Chirimoya, and la Mulatera. These foothill sites were between 17[degrees] 55' 43.50"N and 96[degrees] 56' 11.38"W at 1,062 and 1,216 m asl. The mean annual rainfall in this area is between 650 and 890 mm, and mean annual temperature is between 19 and 23[degrees] C (Rivera-Ortiz et al. 2008).

Food Availability.--We conducted monthly phenological observations between March 2005 and March 2006. We randomly established four 50 x 20 m plots in Santa Marfa Tecomavaca, and three plots each in oak and tropical dry forest vegetation types in San Juan Coyula that were surveyed each month. Area surveyed was selected after performing a minimum area test. All trees, shrubs, and cacti >5 cm diameter at breast height (DBH) were marked in each plot and numbers of fruits were recorded for each month throughout the year. A series (5-10) of samples (i.e., branches) were counted for trees with abundant fruits, and the number of total branches was counted to calculate the total number of fruits (Chapman et al. 1992, Borchert 1994). Relative abundance of trees in plots was calculated for trees where macaws fed during the year. Relative abundance of...

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