Conservation puzzle: Endangered hyacinth macaw depends on its nest predator for reproduction

https://doi.org/10.1016/j.biocon.2007.12.023Get rights and content

Abstract

In the Pantanal wetlands of Central Brazil, the endangered hyacinth macaw (Anodorhynchus hyacinthinus), the largest psitacid in the world, makes its nest almost exclusively in natural hollows found in the manduvi tree (Sterculia apetala). The recruitment of manduvis greatly depends on the seed dispersal services provided by the toco toucan (Ramphastos toco), responsible for 83.3% of the seed dispersal. The toco toucan, however, is responsible for about 53% of the preyed eggs, resulting in a case of conflicting ecological pressures in which the reproduction of the hyacinth macaw is indirectly dependent on the seed dispersal services of its nest predator. The case illustrates the intricacies of biotic interactions in species-rich environments where species may be tied by indirect, subtle ecological links which conservationists should be aware of.

Introduction

Hyacinth macaw (Anodorhynchus hyacinthinus) is the largest psitacid in the world, currently considered endangered because the remaining small populations are undergoing very rapid reductions as a result of illegal trapping and habitat loss (Snyder et al., 2000, BirdLife International, 2004). As a large, secondary cavity nester, hyacinth macaws need large, pre-existing tree holes for nesting (Guedes and Harper, 1995). Because such nesting sites are naturally scarce, their availability is an additional conservation problem (Guedes and Harper, 1995, Snyder et al., 2000).

In the Pantanal wetlands of central South America, home of the largest population of hyacinths, manduvi trees (Sterculia apetala (Jacq.) Karst; Malvaceae) provide the bulk (95%) of nesting sites (Guedes and Harper, 1995). Competition for nest cavities with other cavity-nesting birds (approximately 17 bird species use manduvi cavities for reproduction; Guedes, 2002), mammals, and even honey bees is intense (Snyder et al., 2000). Competition among breeding hyacinth macaw pairs is exacerbated because only trees older than 60 years produce cavities large enough to be used by the macaws (Santos et al., 2006). Provisioning of nesting boxes is thus a conservation strategy that is being used for the species (Snyder et al., 2000, Guedes, 2004).

The manduvi is one of the tallest trees in the Pantanal (20–35 m height), where it grows in forest patches (semideciduous and gallery forest) that cover only 6% of the vegetation area of the Pantanal (Silva et al., 2000). From July to September manduvi trees produce large fruits that open to expose three to eight bird-dispersed seeds (23.8 mm length × 14.2 mm wide, n = 20) with an oily aril. The species is not safe from threats, because the traditional extensive cattle ranching, the main economic activity in the Pantanal, is being rapidly replaced by more intensive ranching models, leading to the degradation of the natural vegetation through deforestation and forest fragmentation (Seidl et al., 2001, Harris et al., 2005). The intensive cattle ranching represent a problem for recruitment in manduvi populations because cattle trample and eat manduvi seedlings, thus reducing seedling densities in areas with high cattle load (Johnson et al., 1997).

The surmounting importance of manduvis to a critical phase of the life cycle of hyacinth macaws stimulated us to study the seed dispersal of this tree. The results surprisingly revealed a system of conflicting ecological pressures in which the availability of nesting sites for hyacinth macaws is directly dependent on the seed dispersal services of its major nest predator, the toco toucan (Ramphastos toco).

Section snippets

Study area and observations of seed dispersers

The study took place at Fazenda Rio Negro (19°34′29″S; 56°14′37″W), located in the Nhecolândia region of the Brazilian Pantanal. The Pantanal is a UNESCO Biosphere Reserve and a Brazilian National Heritage site of international relevance according to the RAMSAR Wetlands Areas Convention. Fazenda Rio Negro is a well-preserved private ranch of 7500 ha free of cattle since 2001, with habitats that represent the main vegetation types of Pantanal (Prance and Schaller, 1982), including cerrado – the

Results

A total of 14 bird species fed on manduvi fruits (Table 1). Half these birds were psitacids that cracked and preyed on the seeds. The remaining species were either gape-limited and unable to swallow whole seeds (e.g. plush-crested jay Cyanocorax chrysops and silver-beaked tanager Ramphocelus carbo), or pulp-consumers that only picked off pieces of aril and rarely carried away a seed in the bill for further consumption (e.g., purplish jay Cyanocorax cyanomelas, and crested oropendola Psarocolius

Discussion

Among birds, habitat and feeding specializations are good predictors of the risk of extinction (Sekercioglu et al., 2004). Hyacinth macaws scores high in what concerns feeding specialization, eating exclusively the fruits of two palm species, Attalea phalerata and Acrocomia aculeata (Guedes and Harper, 1995). It also scores high in nest site specialization, selecting predominantly manduvi tree holes to set their nests. Given the current land use trends in the Pantanal (Seidl et al., 2001,

Acknowledgments

We thank Pedro Jordano, Rodolfo Dirzo, Douglas Levey, Harry Greene, and Nelson Guda for helpful comments. D.J. Brightsmith and one anonymous referee for improving the final version of this paper. Alexine Keuroghlian, Alexander V. Christianini, and Earthwatch volunteers helped in many ways during the fieldwork. Ellen Wang took the picture that illustrates Fig. 1. Renato M. Marques helped with density calculations. Financial support came from Conservação Internacional do Brasil, Earthwatch

References (16)

  • A.F. Seidl et al.

    Cattle ranching and deforestation in the Brazilian Pantanal

    Ecological Economics

    (2001)
  • BirdLife International, 2004. Anodorhynchus hyacinthinus. In: IUCN, 2007. 2007 IUCN Red List of Threatened Species....
  • S.T. Buckland et al.

    Distance Sampling, Estimating Abundance of Biological Populations

    (1993)
  • C.I. Donatti et al.

    Living in the land of ghosts: fruit traits and the importance of large mammals as seed dispersers in the Pantanal, Brazil

  • Guedes, N.M.R., 2002. El proyeto del Guacamayo jacinto Anodorhynchus hyacinthinus en el Pantanal sur, Brasil. In: V...
  • Guedes, N.M.R., 2004. Araras azuis: 15 anos de estudos no Pantanal. In: Soriano, B.M.A., Sereno, J.R.B., Sarath, E.L.,...
  • N.M.R. Guedes et al.

    Hyacinth macaw in the Pantanal

  • M.B. Harris et al.

    Safeguarding the Pantanal wetlands: threats and conservation initiatives

    Conservation Biology

    (2005)
There are more references available in the full text version of this article.

Cited by (0)

View full text