Veredas and their use by birds in the Cerrado, South America: a review

Veredas e seu uso por aves no Cerrado, América do Sul: uma revisão

THEMATIC REVIEWS

Veredas and their use by birds in the Cerrado, South America: a review

Veredas e seu uso por aves no Cerrado, América do Sul: uma revisão

Dárius Pukenis Tubelis^*

Departamento de Ecologia, Instituto de Biociências, Rua do Matão, 321, Universidade de São Paulo - USP, CEP 05508-900, São Paulo, SP, Brazil

ABSTRACT

In the Cerrado, veredas are linear physiognomies that occur on hydromorphic soil usually along narrow water courses. They often growth on flat terrain or near headwaters. They are characterised by the abundance of buriti palms (Mauritia flexuosa) that growth over other trees, numerous shrubs and a dense herbaceous stratum. Despite being common landscape elements through the Cerrado's extension, the use of veredas by birds has not been examined in detail. This study aimed to review studies of birds and veredas in the Cerrado. Publications (n = 25) reported the use of veredas by 261 bird species. Only 13 of them had aspects of their biology (reproduction and feeding) studied in detail. Veredas are poorly used by Cerrado's endemic species, but are the major habitat requirement of several species. The richness of bird species found in veredas is increased by their inclusion in the home range of forest, savanna and grassland species. This study also discusses the values of veredas to the regional biodiversity, and the major threats to their conservation inside and outside the system of nature reserves. Suggestions for future research on birds and veredas in Cerrado also are provided.

Keywords: grassland, landscape, Mauritia, savanna, wetland.

RESUMO

No Cerrado, veredas são fisionomias com formato linear que ocorrem em solos hidromórficos geralmente ao longo de estreitos cursos d'água. Crescem usualmente em relevo plano ou próximo a nascentes. São marcadas pela abundância de buritis (Mauritia flexuosa), que se destacam sobre outras árvores, arbustos, e um denso estrato herbáceo. Apesar de serem comuns elementos de paisagens em toda a extensão do Cerrado, o valor de veredas às aves ainda não foi examinado em detalhe. Este trabalho teve como objetivo revisar os estudos envolvendo aves e veredas no Cerrado. Publicações (n = 25) mencionaram o uso de veredas por 261 espécies de aves no Cerrado. Somente 13 dessas espécies tiveram aspectos de sua biologia (reprodução ou alimentação) estudados em detalhe. Veredas são pouco usadas por espécies endêmicas do Cerrado, mas são o principal requerimento de hábitat de algumas espécies de aves. A riqueza de espécies de aves encontrada em veredas é em grande parte aumentada pela sua inclusão na área de vida de espécies florestais, savânicas e campestres. Este estudo também discute os valores de veredas à biodiversidade do Cerrado, e as principais ameaças à sua conservação dentro e fora do sistema de reservas naturais. Também são fornecidas sugestões para pesquisas futuras envolvendo aves e veredas no Cerrado.

Palavras-chave: área úmida, campo, Mauritia, paisagem, savana.

Introduction

Vegetation physiognomies with numerous palm trees are remarkable landscape elements in several tropical regions. Among them are palm forests in South America, forests of babaçu and buriti palms in southern Amazon and veredas in central Brazil (Eiten 1993, Stotz et al. 1996, Rizzini 1997).

Veredas are linear and common landscape elements widely distributed through the naturally patchy environment of Cerrado - the savanna ecosystem that dominates central Brazil (Eiten 1993, Oliveira & Ratter 2002). They are open vegetation physiognomies characterised by the presence of numerous buriti palms (Mauritia flexuosa), a dense herbaceous stratum and a diverse range of shrubs and trees (Ribeiro et al. 1983, Ribeiro & Walter 1998, Oliveira & Ratter 2002). They occur on hydromorphic soil usually along narrow water courses (Motta et al. 2002, Oliveira & Ratter 2002). Veredas harbor a considerable species richness of grasses, shrubs and trees (Silva & Felfili 1998, Filgueiras 2002). Also, veredas are among the habitat requirements of a diverse range of wildlife (Villalobos 1994, Marinho et al. 1998, Bonvicino et al. 2005, Gurgel-Gonçalves et al. 2006).

Birds have been investigated in detail in veredas since the 1940s. For example, Sick (1948a, b) examined the breeding biology of two swift species in Mato Grosso. In this same region, Sick (1955) examined the distribution of bird species in different vegetation physiognomies, including veredas. In his review of Cerrado's wildlife, Sick (1965) provided a list of bird species typical of veredas (buritizais). More recently, Antas & Cavalcanti (1988) elaborated the first field guide of identification of bird species commonly found in central Brazil. In this book, they provided information on the use of buriti palms and veredas by birds.

Numerous studies, encompassing a wide range of topics of research, have been conducted in more recent decades. Among them is a detailed research on the feeding ecology of birds in a vereda in the Brazilian Federal District (Villalobos 1994). The breeding biology of Ara ararauna was investigated in Goias state (Bianchi 1998). The arthropod fauna associated to the nesting of Phacellodomus ruber was examined in the Federal District (Gurgel-Gonçalves et al. 2004, 2006, Gurgel-Gonçalves & Cuba 2007). Further, some studies compared the bird species composition of veredas with those of physiognomies such as forests and savannas in northern, central and southeastern Cerrado (Silva et al. 1997, Bagno & Marinho 2001, Santos 2001, Franchin & Marçal 2004, Valadão et al. 2006). Additionally, brief information on the biology of species found in veredas has been reported in publications focusing a wide range of aspects of birds in the Cerrado (e.g., Willis & Oniki 1993, Silveira et al. 2001, Blamires et al. 2005).

Despite these numerous studies, the use of veredas has received little or no attention in major reviews about the avifauna found in Cerrado (Cavalcanti 1988, Silva 1995, 1997, Macedo 2002, Silva & Bates 2002, Silva & Santos 2005). As they emphasised the use of forests, savannas and grasslands, the use of veredas by birds has not been reviewed in detail.

This study aimed to review information on birds and veredas in the Cerrado province. First, I compiled and characterised the studies containing this information. Then, I examined the use of veredas by species, and reviewed the major results brought by these publications. The information was evaluated to identify ecological patterns and lacunes of knowledge. Also, I present a general overview considering most information on birds and studies concerning aspects of the biodiversity and conservation of veredas in the Cerrado. Finally, I provide suggestions for future research on veredas and birds in the Cerrado.

Methods

1. Cerrado

This vegetation province occupies near 2,000,000 km² in Brazil, Paraguay and Bolivia (Figure 1). It dominates the highlands of central Brazil and extends through peninsulas and isolated patches to the Atlantic Forest, the Amazon, the Chaco and Caatinga (Eiten 1972, IBGE 1993, Oliveira & Marquis 2002).

The vegetation cover of landscapes in Cerrado is usually dominated by cerrado sensu lato, a gradient of physiognomies ranging from grasslands to woodlands and forests (Eiten 1972, Coutinho 1978, Ribeiro & Walter 1998, Oliveira & Ratter 2002). Cerrado sensu lato is the matrix of uplands, where semi-deciduous forests, deciduous forests and rocky grasslands usually cover smaller areas. Gallery forests, marshes, floodplain grasslands and veredas occur in valleys (Ribeiro et al. 1983, Eiten 1993, Oliveira & Ratter 2002). Climate is tropical and strongly seasonal, with well defined dry and wet seasons (Assad 1994). The Cerrado is influenced by natural and man-made fire (Coutinho 1994, Miranda et al. 2002, 2004). Additional information on the Cerrado's environment can be found in Oliveira & Marquis (2002) and Scariot et al. (2005).

2. Veredas

Veredas are linear vegetation physiognomies (Figure 2) that occur commonly and widely through the Cerrado extension (Ribeiro et al. 1983, Eiten 1993, Ribeiro & Walter 1998). They often growth along narrow water courses on flat terrain, in the middle of topographic sequences between gallery forests and cerrado, or near headwaters (Silva & Felfili 1998, Oliveira & Ratter 2002). They grow on hydromorphic soil, where the water table reaches or almost reaches the surface during the rainy season (Motta et al. 2002, Oliveira & Ratter 2002). Veredas are open physiognomies characterised by: 1) numerous buriti palms (Mauritia flexuosa) composing most of the arboreal stratum, 2) the presence of shorter trees and shrubs forming groups or not, 3) a dense herbaceous stratum (Eiten 1993, Ribeiro & Walter 1998, Silva & Felfili 1998, Oliveira & Ratter 2002). A high diversity of plants can be found in veredas (Silva & Felfili 1998, Filgueiras 2002, Meirelles et al. 2004).

3. Literature review

All studies found that contained information on the use of veredas by birds in the Cerrado province (considering its extension in Brazil, Bolivia and Paraguay) were included in this review. The literature review included peer-reviewed articles published in scientific journals until 2007. Their search was mainly based on Oniki & Willis (2002), the Web-of-Science and Google Schoolar. PhD and Master theses, scientific books (including identification guides) and their chapters also were considered.

Results and Discussion

1. Types of study

Publications (n = 25) reviewed in this study include articles of scientific journals (n = 17), theses (n = 2), book chapters (n = 3) and books (n = 3). Both theses and five scientific articles had birds and veredas as their major focus of research (Sick 1948a, b, Villalobos 1994, Bianchi 1998, Gurgel-Gonçalves et al. 2004, 2006, Gurgel-Gonçalves & Cuba 2007). On other hand, eight publications compared the occurrence of species in different physiognomies, including veredas (e.g., Sick 1955, 1965, Negret et al. 1984, Silva et al. 1997, Bagno 1998, Santos 2001). Other reviewed publications provided only brief comments on species occurrence or aspects of bird biology in veredas. They include books and short communications (e.g., Willis & Oniki 1993, Sick 1997, Silva & Silva 2004).

2. Regional distribution of studies

Records of birds in veredas are widespread through Cerrado (Figure 1). A relatively high number of studies have been conducted in its central portion: Goias State and the Federal District (e.g., Antas & Cavalcanti 1988, Bagno 1998, Bianchi 1998, Bagno & Marinho 2001, Gurgel-Gonçalves & Cuba 2007, Curcino et al. 2007). Investigations in northern Cerrado were in the states of Amapa (Silva et al. 1997) and Piaui (Santos 2001, Silveira et al. 2001). Studies conducted in western Cerrado were in Mato Grosso (Sick 1948a, b, Sick 1955). Other studies involved records in Minas Gerais state, southeastern Cerrado (Franchin & Marçal 2004, Valadão et al. 2006, Vasconcelos et al. 2006). Other publications have not informed the regions or localities where records were obtained (e.g., Sick 1997, Silva & Silva 2004). No studies examined regional variation in the use of veredas by birds.

3. Species richness and composition

A total of 261 bird species of 18 orders and 53 families were detected in veredas in the Cerrado (^{Appendix 1}). Passeriformes, Falconiformes and Charadriiformes were orders with more species. Families with the highest species richness were Tyrannidae, Emberizidae, Psittacidae, Thraupidae and Accipitridae, with 34, 19, 17, 15 and 12 species, respectively (^{Appendix 1}).

The proportion of bird assemblages that use veredas could be assessed at three spatial scales. After discarding those studies conducted outside the Cerrado core area, an evaluation at a macro scale could be done. Of the 846 bird species found in the Cerrado core area (Silva 1995, Silva & Santos 2005), 254 (30%) were recorded in veredas (^{Appendix 1}). As this is the first study to compile records of bird species for an only physiognomy in the Cerrado, comparisons with other vegetation are not possible.

The bird species richness recorded until now in veredas in the Cerrado (^{Appendix 1}) should be considered as underestimated due to some reasons. First, several studies that greatly contributed to the knowledge of regional or local avifaunas (e.g., Willis & Oniki 1990, 1991, Bagno & Marinho 2001, Kirwan et al. 2004, Narosky & Yzurieta 2006, Silva et al. 2006, Pacheco & Olmos 2006) have not pointed out those species detected in veredas, despite having sampled these physiognomies. Second, field guides of South American birds (e.g., Ridgely 1989, 1994, Sigrist 2006) reported the occurrence of species in palm groves (including those of Mauritia trees) but have not informed if records occurred within Cerrado. Third, some books (e.g., Antas & Cavalcanti 1988) have identified species that use buritis palms, without informing the physiognomies where records were obtained. As buriti palms also occur in gallery forests, savannas and grasslands close to veredas, some of their records were not included in Appendix 1. Fourth, studies on veredas are not numerous and often involved relatively short sampling periods or a low number of sites (veredas).

The proportion of species that use veredas also could be assessed at a regional scale. Of 429 species recorded in Brazil's Federal District, 57 (13%) were noted using veredas (Negret et al. 1984). Bagno & Marinho (2001) reviewed information on birds of this same region and reported that 22% of the species use veredas. Santos (2001) has reported that 26% of species recorded in the region of Chapada das Mangabeiras were observed in veredas.

Assessments at smaller scales could be done considering the species composition of protected portions of landscapes. In the experimental campus of Embrapa, in Amapá, 37 species (14%) were found in veredas (Silva et al. 1997). At Estação Ecológica de Águas Emendadas, central Cerrado, 86 (30%) of the 287 recorded species were observed in veredas (Bagno 1998). Bird species found in veredas comprised 73% and 80% of the avifaunas of two urban parks in southeastern Cerrado (Franchin & Marçal 2004, Valadão et al. 2006).

A comparison of these assessments reveals a substantial variation in the values of representativeness (13-80%) of species that use veredas to the composition of local or regional avifaunas. Factors related to this wide range of proportions might be related to characteristics of veredas, landscapes and sampling. The number of veredas in a given landscape mosaic, variation in the structure and floristics of veredas and the juxtaposition to other physiognomies might influence the bird species composition found in veredas in different studies. Also, these assessments have not standardized the sample efforts in the different physiognomies. Thus, the contribution of bird species that use veredas to the species composition of local or regional assemblages could have been under or overestimated.

4. The use of veredas and other physiognomies

All species detected in veredas (^{Appendix 1}) also can be found in other vegetation physiognomies or water bodies in the Cerrado (Negret 1983, Silva 1995, Sick 1997, Silva et al. 1997, Bagno 1998, Melo-Junior et al. 2001, Tubelis & Cavalcanti 2000, 2001, Bagno & Marinho 2001, Sigrist 2006). The absence of species restricted to veredas might result of four reasons. First, great part of the species richness found in veredas is composed of species that inhabit other physiognomies and use veredas as additional habitat. For example, Galbula ruficauda, Picumnus albosquamatus, Cnemotriccus fuscatus, Synallaxis frontalis and Turdus spp are forest species (Negret 1983, Lins 1994, Sick 1997, Tubelis et al. 2004a) that were recorded in veredas (^{Appendix 1}). Specimens of these and other forest birds might leave gallery forests occasionally to use nearby veredas. Similarly, species that require mainly savanna woodlands (campo cerrado and cerrado sensu stricto) for survival, such as Suiriri suiriri, Cyanocorax cristatellus, Troglodytes musculus and Cariama cristata (Sick 1997, Tubelis & Cavalcanti 2001, Amaral & Macedo 2003, Lopes & Marini 2006) also might include veredas in their home ranges (^{Appendix 1}). Also, individuals of species that require mainly grasslands and savannas (Tubelis & Cavalcanti 2001), such as Rhynchotus rufescens, Ammodramus humeralis and Emberizoides herbicola also might use veredas if living close to them. Thus, part of the bird species richness found in veredas is due to the use of veredas as additional habitat by individuals living in forests, savannas and grasslands close or adjacent to veredas.

Second, some bird species found in veredas also have other elements of Cerrado's landscapes as their major habitat requirements. For example, aquatic bird species such those of the families Ardeidae, Anatidae, Rallidae, Scolopacidae and Alcedinidae also live in marshes, streams, rivers and other wet physiognomies. Similarly, species such as Orthopsittaca manilata, Ara ararauna, Phacellodomus ruber and Schisthochlamis melanopis also are found in other vegetation physiognomies, such as forests, babaçuais and savannas (Sick 1955, 1965, Ridgely 1989, 1994, Sick 1997, Erize et al. 2006, Sigrist 2006).

The third reason for the absence of species restricted to veredas is related to their linear format. As veredas are usually narrow landscape elements, birds might find difficulties in establishing long and narrow home ranges or territories within their limits, as suggested by the central place foraging theory (Pyke et al. 1977, Tubelis et al. 2004b). Related to this, is the fact that physiognomies adjacent to veredas might provide food and other resources for birds whose home ranges are centered in veredas. The seasonal occurrence of trees or shrubs with numerous flowers or fruits is common in gallery forests and savannas (pers. observ.). Also, termite swarms are frequent in grasslands and woodlands during the rainy season in the Cerrado. So, it is expected that birds occasionally leave veredas to adventure in adjacent physiognomies to search for food resources not found in veredas, as reported for forest birds in central Cerrado (Negret 1983, Lins 1994). Several aquatic species as well as Ara ararauna, Orthopsittaca manilata, Chaetura meridionalis, Tachornis squamata, Phacellodomus ruber and Berlepschia rickeri can be considered as examples of these species.

5. Vereda use by species endemic to Cerrado

Of the 36 bird species considered as endemic to the Cerrado region, most are forest species while others are species of open physiognomies of cerrado sensu lato (Silva 1995, Cavalcanti 1999, Macedo 2002, Silva & Bates 2002, Silva & Santos 2005). Only four (11%) of these species were observed using veredas (^{Appendix 1}). Two forest species (Herpsilochmus longirostris and Hylocryptus rectirostris) were observed in veredas of urban parks in southeastern Cerrado (Franchin & Marçal 2004, Valadão et al. 2006). Cyanocorax cristatellus and Saltator atricollis, two species that require mainly savanna woodlands for survival (Sick 1997, Tubelis & Cavalcanti 2001, Amaral & Macedo 2003) also were detected in veredas in central and southeastern Cerrado (^{Appendix 1}). These low numbers of species, records and studies suggest that veredas are not among the major habitat requirements of most bird species endemic to Cerrado. One exception appears to occur with Conothraupis mesoleuca, a poorly known species occasionally found in veredas at Parque Nacional das Emas (pers. com.).

6. Aspects of bird biology investigated in detail in veredas

Detailed investigations on the natural history of bird species in veredas involved their breeding and feeding activities. The breeding biology of four species has been studied in detail in veredas. In September 1946, a Tachornis squamata was observed building a nest in a vereda in the Rio das Mortes region (Sick 1948a). The nest - an elongated clump of feathers glued with mucus - was constructed in a dry buriti leaf and contained three eggs. In a vereda of this same region of Mato Grosso, three nests of Chaetura meridionalis were found in October and November (Sick 1948b). They were open cups fixed to internal walls of trunks of dead buritis and contained four or five eggs.

Five decades later, a more detailed study examined the breeding biology of Ara ararauna at Parque Nacional das Emas (Bianchi 1998). Eighteen nests found in dead buriti palms were monitored. Macaws nested near the top of trunks, where one to five eggs were found. Macaws started the courtship activities and the selection of nest cavities in the beginning of the dry season (May). Egg laying occurred in September and October, and were followed by incubation periods of about 26 days. As consequence, young macaws were able to fly in the early rainy season. About 72% of nesting attempts were successful, and factors involved in nest predation could not be clarified. This study also provided detailed information on the nest cavities used by macaws and on their behavior, courtship, nesting care and eggs (Bianchi 1998).

The nesting of Phacellodomus ruber was examined to verify its association with the occurrence of Hemiptera species in central Cerrado (Gurgel-Gonçalves et al. 2004, 2006, Gurgel-Gonçalves & Cuba 2007). It was found that larger and active nests contained more arthropods than smaller and inactive nests. Authors argued that characteristics such as several incubation cameras per nest, nest re-occupation and life in groups contriute for the abundance of arthropods in buriti palms with nests of P. ruber. Also, the hemipteras found in P. ruber nests were not infected with Tripanossoma cruzi. Gurgel-Gonçalves et al. (2004) also reported the nesting of Caracara plancus and Gnorimopsar chopi in veredas, but details were not provided.

Feeding ecology was other aspect of bird biology researched in detail. In a vereda at Brazil's Federal District, nine frugivorous bird species had their foraging activities examined during a 11-month period (Villalobos 1994). This study has shown that three parrot species (Orthopsittaca manilata, Ara ararauna and Amazona aestiva) are key species in the ecology of trophic guilds of bird and mammal species associated with buriti fruits in veredas. Although these three species tended to exploit fruits in the buriti canopies, they also had a major role in seed dispersion and fruit dropping. As result of their feeding activities, open fruits became available in canopies and were eaten by four bird species (Thraupis sayaca, Schisthochlamis melanopis, Gnorimopsar chopi and Cyanocorax cristatellus). Fruits open by parrots also had parts eaten while on the ground. One specimen of Porzana albicollis collected with a trap had its stomach full of buriti pulp. Caracara plancus was seen with whole fruits in adjacent woodlands, and then considered as a species able to gather fruits from buritis (Villalobos 1994). This was the only study to examine vereda use by birds in different periods of the day. Buritis were visited with similar frequencies in mornings and afternoons by Orthopsittaca manilata and A. ararauna, while A. aestiva was detected only in mornings (Villalobos 1994).

As consequence of these studies, 13 species had their biology investigated in detail in veredas. This number corresponds to only 5% of the bird species richness found in this physiognomy (^{Appendix 1}). With the exception of P. albicollis, these species are land birds. Thus, although numerous aquatic bird species occur in veredas (^{Appendix 1}), research on them is lacking.

7. Overview and conservation issues.

This review highlighted some roles that veredas play for bird assemblages in the Cerrado. First, they are used by a high number of bird species - 28% of the species richness found in the Cerrado core area. Second, veredas function as additional habitat for part of the populations of numerous species that have forests, savannas and grasslands as their core habitats. This could be considered as one more component of the biodiversity found in Cerrado, as home ranges with and without veredas migth be ecologicaly or evolutionary distinct. Third, the compiled information indicates that veredas are poorly used by Cerrado's endemic species. Fourth, no bird species are restricted to veredas. This fact does not imply in absence of habitat specialization. Knowlegement brought in the last two decades suggests that habitat specilization in the Cerrado region should not be though considering a unique physiognomy. Instead, the existence of a core habitat and the use of adjacent physiognomies should be considered, as shown for forest and savanna birds (Cavalcanti 1992, Lins 1994, Silva 1995, Tubelis et al. 2004a). Thus, veredas are the main habitat requirements of several bird species, as argued by scientists with long experience in the Cerrado (e.g., Sick 1955, 1965, 1997).

Besides birds, a wide range of fauna and flora elements can be found in veredas (Villalobos 1994, Marinho et al. 1998, Silva & Felfili 1998, Meirelles et al. 2004). Further, veredas play an important role in the protection of watersheds (Filgueiras 2002). To exemplify this fact, the Estação Ecológica de Águas Emendadas was created with the purpose of protecting the headwaters of two major hydrographic basins in central Brazil (Marinho et al. 1998). Veredas also give an outstanding contribution to the beauty of landscapes in the Cerrado region (pers. observ.). Further, veredas are potential sites for recreation and leisure in protected and non-protected landscapes. This because they provide suitable conditions for pleasant walkings and excellent opportunities for swimming or drinking. Veredas also have the potential for the sustainable exploitation of parts of buriti palms, that are widely used in some Cerrado regions. More importantly, veredas are a unique ecosystem in the Cerrado province, harboring particular species, interactions and ecological processes. Further, veredas are traditionally considered as sites of great importance by rural populations inhabiting Cerrado's landscapes (Rosa 2006). Therefore, numerous aspects of the biotic and abiotic environment of veredas, including their biodiversity and ecosystem services, make them major targets for conservation actions inside and outside the system of nature reserves in the Cerrado.

Despite their values, veredas have been severely modified by human activities. For example, the establishment of agribusiness is a major threat to the Cerrado's biodiversity (Ratter et al. 1997, Klink & Moreira 2002). Only veredas with few meters in width are usually immersed in agricultural landscapes (pers. observ.). Besides being narrow, these vereda remnants might be substantially contaminated with agrochemicals used in exotic plantations, such as those of soyabean and cottom.

Other potential conservation problem concerning veredas is the intense and unsustainable exploitation of buriti resources in some regions, such as Piaui and Maranhão. Buritis have a great economical value, as their parts can have a wide range of use (Almeida et al. 1998, Felfili et al. 2004). For example, in Teresina and other municipalities of northern Cerrado, markets often sell numerous products made with dead and alive parts of buritis (pers. observ.). Although buriti palms are abundant and widely distributed through the Cerrado extension, overexploitation might lead to dramatic negative impacts on wildlife in some regions or localities. Dams are other threat to veredas outside nature reserves. Hydroelectric dams can occasion the complete inundation of veredas. On other hand, small dams made by rural people to store water for drinking or planting (e.g., rice fields) often interrupts the water flow and cover part of the grass layer in veredas (pers. observ.).

Other major threat to the health of veredas is burning by local population. Negative impacts of burning and cattle trampling on the grass layer have been shown by a study in a non-protected landscape in central Cerrado (Meirelles et al. 2004). Unfortunately, burning of veredas has been occurring for decades within the Cerrado's reserve system. Between 2005 and 2007, I visited some nature reserves in northern Cerrado (Maranhão and Piaui states) and found numerous veredas modified by man-made fire. For example, numerous inhabitants of Parque Nacional da Chapada das Mesas and Estação Ecológica Uruçuí-Una burn the grass layer of veredas located in the proximities of their houses. Some of them informed that numerous veredas are drying, and argued that this process occurs due to the frequent burning and logging of their vegetation. At Parque Nacional das Nascentes do Rio Parnaíba, problems appear to be worse. There, great extensions of veredas have their grass layer burned during the dry season to estimulate the regrowth of grasses (Figure 3). After rebrouting, numerous cattle are illegally brought to the park by ranchers to feed on vereda grasses. Despite great effort by park managers, this invernada activity and other illegal actions involving veredas still occur in some Cerrado's reserves.

8. Suggestions for future studies

My suggestions for future research on birds and veredas in the Cerrado can be divided in two major categories. First, are those more related to the biology of birds, the environment of veredas and aspects of Cerrado's landscapes. Other suggestions comprise investigations that consider veredas and their species as indicators of the ecology of birds in naturally patchy environments. They are: (1) identification of species that have veredas as core areas of their home ranges or territories, for detailed investigation of aspects of their natural history still poorly known; (2) the study of the biology of aquatic species, including the examination of their responses and adaptations to the seasonal water availability typical of veredas. This because most detailed studies on the biology of particular species involved forest, savanna or grassland birds; (3) investigations of modification of veredas by agricultural activities (such as reduction of their cover and contamination by agrochemicals) and those involving cattle ranching (such as vegetation burning). The negative impacts of collects of dead and alive parts of buriti palms also could be evaluated; (4) examination of the natural variation in the vegetation structure and floristics of veredas on their use by birds; (5) veredas use as sites for studies of the ecology of patch-matrix movements, landscape supplementation and landscape complementation by birds (Dunning et al. 1992). These studies could include the use of veredas by birds of adjacent forests, woodlands and grasslands, as well as the use of adjacent physiognomies by species of veredas; (6) examination of how birds inhabit these linear and naturally fragmented elements of Cerrado's mosaics, considering the extensive literature on birds in landscapes modified by human activities; (7) use veredas as sites for the study of natal and reproductive dispersal of birds. This aspect of avian biology has rarely been studied in South America and might be successfully conducted in veredas. This because the linear format of veredas and their relatively simple vegetation structure might facilitate the finding of nests and banded birds in consecutive years.

Acknowledgements

I thank Universidade de São Paulo for logistic support and IBAMA for access to several nature reserves in Cerrado. Cintia Cornelius, Simone Bazarian, Carlos Cândia-Galhardo and one anonymous reviewer provided constructive suggestions to this manuscript. I received financial support from FAPESP (process no. 05/00773-3) and CNPq (471360/2006-6) during the elaboration of this manuscript.

Received 06/02/09

Revised 22/06/09

Accepted 08/08/09

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Appendix 1 

Publication Dates

• Publication in this collection
  26 Jan 2010
• Date of issue
  Sept 2009

History

• Accepted
  08 Aug 2009
• Reviewed
  22 June 2009
• Received
  06 Feb 2009