Parrots as overlooked seed dispersers

www.frontiersinecology. org © The Ecological Society of America Parrots as overlooked seed dispersers S after our friend and colleague Gary R Bortolotti passed away in 2011, his widow Heather Trueman sent JLT ten photographs of parrots that Gary had taken in Brazil. In one of these images, we saw a flying chestnutfronted macaw (Ara severus) carrying in its beak a defleshed fruit of the motacú palm (Attalea phalerata; upper-right arrow in Figure 1); upon enlarging this picture for publication in Frontiers, we noticed another macaw transporting a smaller-sized seed (lower-left arrow in Figure 1). Gary’s photograph had captured what has been described as an unusual behavior: active seed dispersal by parrots. The unexpected nature of this observation was reinforced during discussions with colleagues who specialize in avian frugivory and seed dispersal. As they argued – and contrary to well-recognized avian seed dispersers such as frugivorous passerines, trogons, and toucans, which typically swallow whole fruits and disperse seeds after gut passage – parrots handle and destroy fruits in situ to eat the pulp or to gain access to the seeds. Although more than 400 known species of parrot inhabit the world’s tropical ecosystems, only lesser vasa parrots (Coracopsis nigra; Böhning-Gaese et al. 1999) and plain parakeets (Brotogeris tirica; Sazima 2008) have previously been reported to regularly disperse seeds transported in their bills. This has led to the general assumption that parrots are seed predators and thus do not participate in seed-dispersal mutualisms (Fleming and Kress 2013). Because only two parrot species were known to routinely carry seeds in flight, this behavior is considered to be unusual. However, these two species are among the more ancestral (Coracopsis) and more modern (Brotogeris) species within the phylogenetic tree of the Psittacidae family of parrots (Wright et al. 2008), suggesting that this behavior could be well-conserved through the evolution and diversification of this large lineage of birds, but nonetheless overlooked. Parrots often forage in the canopy of tropical forests, and their foraging behaviors are difficult to study due to remote locations and logistical constraints. Thus, the likelihood of observing a parrot in flight carrying a fruit or seed in its bill may be low, and such behaviors may go largely unreported. A new photograph (Figure 2) taken by JLT, this time of a large flock of red-fronted macaws (Ara rubrogenys) in Bolivia, led us to reconsider this second hypothesis. In this case, the transport of an ear of corn (Zea mays) by a macaw went unseen until the photograph was examined more closely. We then decided to reassess the foraging behavior of parrots, searching for indications of other dispersal events. To that end, we joined a group of parrot biologists and ecologists studying foraging behavior who, since 2012, have recorded hundreds of observations of parrots dispersing fruits or seeds using their bills or, less often, their feet (WebFigure 1). Although preliminary, our data suggest that seed dispersal by parrots is not unusual. Observations came from 28 parrot species belonging to 16 genera, ranging in body size from the smallest parakeets to the largest macaws, and involved the dispersal of fruits and seeds from 94 species of trees (including palms) and shrubs. Instances were recorded in seven countries (Argentina, Bolivia, Brazil, Chile, Ecuador, Peru, and Spain), comprising mostly neotropical parrots but also an African and an Asian species from introduced populations of parrots in Spain. They covered a wide variety of ecosystems – from the sea-level Argentinean Pampas to high-altitude Andean forests, from continents to islands, from the wettest Amazonian savannas to the driest Caatinga forests, and from pristine to urban habitats. Regarding functional interactions, parrots – regardless of their origin – dispersed both native and non-native (including cultivated) plants. We measured the distances that fruits or seeds were carried by parrots, with the aid of laser rangefinders, in 686 dispersal events. Unsurprisingly, given the long-distance flying abilities of most parrot species, the distances spanned a wide range (maximum = 1200 m, median = 27 m, mean = 44 m; WebFigure 2). This indicates that parrots may serve as efficient long-distance seed dispersers. Moreover, we observed several incidents where transported NATURAL HISTORY NOTES NATURAL HISTORY NOTES