Introduction

Throughout their tropical and subtropical range of distribution, primates occupy a wide variety of different habitats (Fleagle 1999). Few primate species seem to be confined to a single habitat type, e.g., Theropithecus gelada to montane grasslands (Kawai 1979). Some others may require the presence of a specific habitat type in at least part of their home range, e.g., bamboo forest in Callimico goeldii (Porter and Garber 2004). However, supposed habitat specialization may actually be the result of limited knowledge of a species that can be specified once additional information becomes available (Defler 1994), and may also be the result of incorrect inference and ignorance of relevant literature.

Uakaris (Cacajao), and particularly the Peruvian red uakari (Cacajao calvus ucayalii, previously included within Cacajao calvus rubicundus: Hershkovitz 1987), represent an example of the latter case. In a survey in the Rio Tapiche area in eastern Peru, Fontaine (1978, 1990) encountered Cacajao calvus ucayalii on 3 occasions: 1) in swamp forest or aguajal (swamps dominated by the aguaje palm Mauritia flexuosa); 2) on a restinga (strip of high-ground forest within a low-ground matrix) from where the uakaris fled into an aguajal; and 3) on the edge of an aguajal. Based on these observations only, Fontaine (1981. p. 446), in the first review of Cacajao, claimed that “uakaris prefer and may even be restricted to flooded forests.” This perception of Cacajao calvus ucayalii and of uakaris in general dominates in the primatological literature, despite accumulating evidence to the contrary. In many primatological textbooks and overview articles, uakaris in general are referred to as “flooded-forest specialists” (Table I), with very few exceptions (Sussman 2000). The fact that the first detailed field study on any uakari species reported the closely related white uakari (Cacajao calvus calvus) to be confined to várzea (forest seasonally flooded by white-water rivers; Ayres 1986, 1989; cf. Peres 1997) may have contributed to cementing this incorrect perception of red uakaris as a flooded-forest specialist. Published evidence for the occurrence of Cacajao calvus ucayalii in nonflooded forests seems to be largely ignored. To correct this bias, we reviewed the available information, both published and unpublished, about habitats where Cacajao calvus calvus has been observed. We hope that this review will correct the perception of this taxon as a flooded-forest specialist. Such a correction is necessary both for scientific reasons, e.g., for the interpretation of its morphological and behavioral adaptations, and for the sake of appropriate considerations on the conservation of Peruvian red uakaris.

Table I Examples for statements on Cacajao calvus ucayalii (or Cacajao in general) as flooded-forest specialists
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Methods

We studied the available literature and unpublished reports, and compiled personal observations or personal communications on the habitat of Cacajao calvus ucayalii. For each area, we extracted information on the habitats where Cacajao calvus ucayalii had been observed and categorized these as 1) terra firme forest, 2) flooded forest, and 3) aguajales. We also compiled the available data on population densities and encounter rates to determine whether habitat influences these variables.

Results

The majority of sites where Cacajao calvus ucayalii has been recorded represent terra firme forest (Table II). This holds true even if 1) Quebrada Blanco and the Estación Biológica Quebrada Blanco, which are located on opposite banks of the same river only about 2 km apart, and the nearby sites at Quebradas Cuchara, Palmichal, Tahuaillo, Tangarana, and Tunchío; and 2) Agua Negra and Lago Preto on the Río Yavarí are considered as nonindependent counts, perhaps harboring the same populations of Cacajao calvus ucayalii.

Table II Localities and habitats in Peruvian Amazonia where Cacajao calvus ucayalii has been recorded
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The highest encounter rates for Cacajao calvus ucayalii stem from the Sierras de Contamana (Table II), a site that is not only a terra firme forest, but also has a much higher altitude (600–700 m a.s.l.) than any of the other sites.

Discussion

We here provide clear evidence that Cacajao calvus ucayalii occurs not only in flooded forests, but also in terra firme forests and in areas with a mixture of forest types. The terra firme forests (or bosques de altura in the terminology of Encarnación 1985) include a variety of vegetation types like high terrace forest (bosque de terraza), low hill forest (bosque de colina baja), high hill forest (bosque de colina alta), premontane forest, and aguajales de altura (see also Malleux 1982, for terminology of Peruvian forests) that are all nonflooded. Therefore, one cannot consider Cacajao calvus ucayalii as a flooded-forest specialist, as is commonly reported in the literature. The highest encounter rate and thus probably the highest population density is found at a relatively high altitude (Sierras de Contamana), untypical for the major part of the Amazon lowlands, suggesting that this habitat might be favorable to Cacajao calvus ucayalii. However, because the Sierras de Contamana is an area with very little human disturbance (Aquino et al. 2005), we cannot distinguish whether this factor or favorable habitat accounts for the high encounter rate.

Cacajao calvus ucayalii have large daily ranging distances (>6 km: Bowler 2007; 7.3 km: Leonard and Bennett 1996) and they may migrate seasonally between different habitats, including flooded forests (Bowler 2007). In the Quebrada Blanco area, the nearest seasonally flooded forest is ca. 8–10 km away along the Río Tahuayo and the lower parts of Quebrada Blanco. Given the daily ranging distances quoted above, this forest is in the reach of Cacajao calvus ucayalii. Nevertheless, neither researchers and their field assistants nor local settlers have ever seen these animals in flooded forest along the Río Tahuayo and lower Quebrada Blanco in the last 25 yr.

Aguajales, swamps dominated by aguaje palms (Mauritia flexuosa), occur both in forests subject to inundation and in areas of terra firme (where they are called aguajales de altura; Encarnación 1985). Though Mauritia flexuosa may represent an important food resource for Cacajao calvus ucayalii in some areas (Aquino and Encarnación 1999; Bowler 2007), it is probably not essential for the existence of these uakaris, as indicated by their rarity in the Sierras de Contamana (Aquino et al. 2005).

Altogether, we can reasonably conclude that Cacajao calvus ucayalii is not a habitat specialist restricted to flooded forests. Together with the report by Peres (1997) of Cacajao calvus calvus at a terra firme site, this indicates that habitat requirements and utilization in bald-headed uakaris are much more variable than previously appreciated.

Incorrect perceptions of or misconceptions on aspects of the biology of a primate taxon may have several implications. First, they may lead to erroneous interpretations of the behavioural, ecological, morphological, and physiological adaptations and the evolution of these adaptations. Second, they may lead to bad conservation strategies, particularly when habitat preferences are concerned. Though the first implication is mainly academic, the second one is of strong practical relevance. In a world, where primate habitats are constantly shrinking and an increasing number of primate taxa is getting closer to extinction, accurate knowledge of habitat requirements are amongst the most basic information needed for conservation efforts.