Temporal and spatial variation of richness and abundance of the community of birds in the Pantanal wetlands of Nhecolândia ( Mato Grosso do Sul , Brazil )

The Pantanal wetlands represent one of the largest flood plains in the World, with extreme climatic variations between dry and wet seasons. The area shelters a high diversity of habitats, representing the main formations found in this sub-region: grasslands, savannah, forested savannah, riparian forests, bays and salines, and Negro river itself. This habitat variability determines the structure and dynamics of the bird community, because most species are closely related to specific habitats. For this, we studied the abundance of bird species from 2001 to 2004 in a Pantanal area of Fazenda Rio Negro, Aquidauana, Brazil. The abundance was compared among those four consecutive years, seasons (dry and wet), time of the day (morning and afternoon), and also between seven different habitats, in order to determine the variation in distribution patterns and habitats used by birds. For this, we used the linear transect method in each of the seven habitats, and recorded bird abundances to obtain richness. The richness registered in the mosaic of habitats was of 201 species for the savannah, 87 in forested savannah, 116 in the riparian forest, 75 in grasslands, 120 in bays, 92 in the salines and 64 in the Negro river, accounting for 348 species in the Pantanal of Rio Negro. Overall, 98 species of migratory birds were registered. The results highlighted some important issues regarding the total abundance of birds in Nhecolândia: Psittacidae was the most abundant family in the region, with prominence in all environments. Recurvirostridae, a monospecific family, showed expressive abundance due to the dominance of Himantopus mexicanus in the salinas, followed by Ardeidae, Anatidae and Cracidae. Other families with high abundance were Tyrannidae, Columbidae, Thraupidae and Emberizidae, all in predominantly terrestrial environments. Moreover: a) The highest number of specimens was recorded in the morning period and in the dry season, regardless of the habitat; b) there were no differences in abundance in the same habitat along the years, but the abundance was different among habitats. In general, the results indicated that there is a relatively stable bird population in each habitat along the annual cycle, but there were differences in abundance among habitats. Thus, additional studies on food availability in dry and wet seasons should be better explored in the future, either in this region or in other Pantanal regions. This fact could better explain the seasonal dynamics of the richness and abundance of birds in the Pantanal area in general. Rev. Biol. Trop. 65 (4): 1358-1380. Epub 2017 December 01.

The Pantanal wetlands stand out for being one of the largest flood plain in the world, in which extreme climatic variations occur between dry (April to September) and wet seasons (October to March).During the wet season, large areas are flooded (Por, 1995).In the sub-region of Nhecolândia, the terrain, together with the rainfall conditions, is considered a predominant factor, for the formation of permanent or temporary lagoons in low terrains, with transition to grassy formations, fields, savannahs and forest formations in higher numbers when compared to other sub-regions of the Pantanal (Alho, Lacher Jr, & Gonçalves, 1988;Ratter, Pott, Pott, Cunha, & Haridasan, 1988;Rodela, 2006).
The Pantanal is a complex of phyto-physiognomies that comprises numerous types of terrestrial and aquatic formations with the most diverse characteristics.In the terrestrial habitat, seasonal deciduous or semi-deciduous forests (including forest islands known as "capão" and riparian forests), fields of "murundus" (circular or elliptical micro topographies present on drainage slopes and headwaters, that remain temporarily or permanently flooded by rainwater; they are small usually round mounds, that often present with soil and vegetation different from the surrounding level area; Resende, Araújo, Oliveira, Oliveira, & Ávila, 2004) and savannah formations with several levels of arboreal, shrub and graminoid coverings (including flooded monodominant formations) (Pott & Silva, 2015).In the aquatic habitat, rivers, fresh or salty water (salines) of different sizes and limnological conditions, permanent flooded fields, as well as the vast intermittent drainage meshwork -meanders, low levels, oxbow lakes, and "corixos" (seasonal streams) -which act as expansion and contraction shafts of the water during the flood periods (Pott & Silva, 2015).Amongst these characteristics, the number of lagoons and lakes is quite peculiar to this complex, numbering in the tens of thousands along its extension (Por, 1995).In the South-Central region of the Pantanal wetlands, two sub-sections marked by the great occurrence of fresh water (bays) and salty (saline) lagoons stand out: Paiaguás, at the North of the Taquari River, and Nhecolândia, at the South of the same river (Tomás, de Salis, Catella, Santos, & Nunes., 2007).
Aiming to broaden the knowledge of the bird community of the Southern region of Pantanal, this work registered the abundance of birds in a mosaic of habitats in the Pantanal of the Rio Negro.It is a pristine area where there is no cattle rising, unlike the other farms in the region; moreover, there is little human influence, and it has become a relevant model area and a unique reference for research.Thus, data from annual, seasonal, time of day, and habitat variation of abundance of the community of birds were collected in order to determine whether there is any variation in the patterns of distribution and use of habitats by birds in the Fazenda Rio Negro, Pantanal de Rio Negro, Nhecolândia, Aquidauana, Mato Grosso do Sul, Brazil.

Area of study:
The study was developed in the Pantanal of Nhecolândia (Fig. 1A and Fig. 1B), in the Fazenda Rio Negro, city of Aquidauana,MS (19º30'00'' S & 56º12'30'' W).The Pantanal of Nhecolândia is a region with lands higher than the surroundings areas, characterized by moderated, localized and of short duration floods, where the bays and salines are distributed in a very heterogeneous matrix (Adámoli apud Por, 1995).The Fazenda Rio Negro contains 8 004 hectares, of which 7 000 belong to RPPN (Private Natural Heritage Reserve) Fazenda Rio Negro, where the sampling plots were concentrated.
The region has a tropical semiarid climate, with an average annual rainfall of 1 180 mm and average temperature varying between 21 and 28 ºC (Marengo, Oliveira, & Alves, 2016).In the Fazenda Rio Negro, the average annual temperature is 26.6 ºC, with a defined dry season between the months of April and September.The Fazenda Rio Negro shelters seven types of habitats, representing the main formations found in the sub-region of Pantanal wetlands: riparian forests, savannah, forested savannah, grasslands, bays, salines and Negro river (Fig. 2).Riparian forests occur along watercourses throughout the drier regions of the Neotropics.These forests contain a diverse association of deciduous and semi-deciduous trees and are seldom larger than 100 m wide.Savannah is the widely used name for the non-forested vegetation that covers much of the Brazilian shield and ranges from open grasslands ("campo sujo") to dense woodlands (forested savannah, treated in this paper as a separate habitat type).Forested savannah is dense woodland consisting of trees and shrubs with thick, fireresistant bark, twisted trunks and large leaves; it contains a nearly continuous ground cover of grasses, sedges and forbs and is designated as dry forest or "cordilheiras" in the Pantanal region.Grasslands support a rich variety of herbaceous vegetation of more than 200 species of grasses and graminoid species; grasslands cover vast areas of Northern and Southeastern Bolivia and adjacent Brazil.Salines are small, rounded ponds, or typical "soda lakes" in which the predominant salt is sodium carbonate, with pH values that may reach 10, and nitrogen that occurs almost exclusively in the form of ammonia (Por, 1995).Bays are natural freshwater spots, circular or elongated shaped and isolated by small elevations on ground, covered or not by vegetation.Waters from various bays connect to each other through small passages ("corixos" and "vazantes"), forming a coalescent system during the flood.The Rio Negro is a tributary of the Paraguay river, with 30 km extension that is between 10 and 50 m wide along its course.
Bird sampling: We used the linear transect method (Bibby, Burgess, & Hill, 1992) for each of the seven habitats (riparian forest, savannah, forested savannah, grassland, bays, salines and river) from 2001 to 2004.During the 17 expeditions to the Fazenda Rio Negro, each habitat was visited twice.At each visit, we conducted two surveys (one in the morning and one in the afternoon), for two hours each period, for a total of 952 hours of linear transects performed in all habitats, (i.e., 4 hours per survey, seven habitats, two surveys per visit, 17 expeditions).Transects were distributed as follows: 2001 (January, April, June and August); 2002 (January, February, April, June, September); 2003 (January, August, November, December); 2004 (April, August, October and December).The transect methodology is widely used in bird studies in a variety of habitats and for different purposes.In general, transects are used in areas of easy access and locomotion as shown by Barrantes, Ocampo, Ramírez-Fernández and Fuchs (2016) in fragments of forest in Costa Rica.Silva and Rodrigues (2015) measured density and spatial distribution of shorebirds in the Brazilian Amazonian coast.Devault, Kubel and Rhodes (2009) monitored birding communities at small airports in the United States.Whitaker and Montevecchi (1996) surveyed breeding bird assemblages in riparian edge, nonriparian edge (clearcut or access road) and in forests in Canada.Herkert (1994) researched the influence of area and vegetation structure on breeding bird communities associated with grassland fragments in Illinois; and the transect method is also used in areas with intensive agriculture as studied by Atkinson, Fuller, Gillings and Vickery (2006).Some general patterns were followed to develop the transects: 1) Routes were selected according to accessibility and were of a fixed length (2 km each) so each could be covered in a session of fieldwork (two hours); 2) surveys were done since dawn (around 6:00) and in late afternoon (from 05:00) to sunset; 3) they were fixed so that we could have replicas of each transect effected; 4) they were performed on consecutive days for each environment twice, totaling 10 days (with two separate teams to develop the samplings); 5) Each team was composed of six to ten participants depending on the location of the transect (the transect in the river was always composed by six participants according to the places available on the boat).6) Care was taken not to record more than one contact for the same individual by monitoring location and dislocation.7) Migratory species may be summer (wet season from October to March) or winter (dry season from April to September) visitors.8) Equipment: we used 8X30, 10X40 and 12X40 binoculars from Swarovski, Nikon and Bushnell brands; Swarovski ATS-65 HD 2.6 "/ 65 mm Spotting Scope and Ecotone 16.5-75X 80 mm for bird registration in salines and bays; Sony TCM 5000 EV, and TC-D5 Prof II for recordings of vocalizations with microphones Sennheiser M66 and ME67.We used ten mist-nets ranging from 20 to 36 mm and length ranging from 8, 12 and 18 m.The mist-nets were used as a complement to the qualitative study so that we could obtain maximum richness, particularly in closed environments where it was not possible to observe/listen to certain birds.It is a complementary study to the transect method, and was carried out simultaneously with another team.Classification of the species followed the official list of Brazilian birds, ruled by the Brazilian Committee of Ornithological Records (Piacentini et al., 2015).
Repeated measures ANOVAs were used to compare total abundance of birds among years, season and times of day because we repeated the surveys each year.A total of four repeated measures two-way ANOVAs were performed: 1) to evaluate the effect of the year, the time of day (morning or afternoon) and the interaction between year and time of day in the total abundance; 2) the effect of the year, the season (dry or wet) and the interaction between the year and the season in total abundance; 3) the effect of the year, the habitat and the interaction between year and habitat in the total abundance; and 4) the effect of the year, the categorized habitat (open, i.e., areas with fewer tree cover as grasslands; and closed, i.e., areas with greater tree cover, such as riparian forests and forested savannah) and the interaction between habitat and year in the total abundance.Once a statistically significant effect was identified, we used Tukey post-hoc test (for multiple comparison of measures).All tests were two-tailed, and the differences were considered significant at P < 0.05.

Richness:
The richness registered was 201 species for the savannah, 87 in forested savannah, 116 in the riparian forest, 75 in grasslands, 92 in the salines, 120 in the bays and 64 in Rio Negro, accounting for 348 species in the Pantanal do Rio Negro (Appendix 1).About 80 % of these species occurred in one or two habitats, 7 % in three, 9 % in four, 1 % in five and less than 1 % in all of them.There were still 2 % of the species that did not belong to any specific habitat, because they generally occupied the air space (Appendix 1).The savannah showed the highest number of exclusive species (67 species), while only four exclusive species were recorded for the forested savannah.A total of 22 exclusive bird species were recorded in the grasslands, 25 in the riparian forests, 14 species in the river, nine in the salines and only two species at bays (Appendix 1).
We found significant variation on richness among years (F 3,219 = 14.757,P < 0.001), among habitats (F 6,219 = 30.886,P < 0.001), and in the interaction between different years and habitats (F 17,219 = 3.505, P < 0.001).The post-hoc Tukey test displayed clusters of habitats based on richness: one composed only by the grasslands, one composed by bays, forested savannah, salines and gallery forest, and the last one composed by savannah and river.When we examined variation between seasons, we found differences among years (F 3,221 = 3.576, P = 0.015) and on the interaction between different years and seasons (F 3,221 = 6.070,P = 0.001), but we did not find any variation between seasons (F 1,221 = 3.116, P = 0.078).Once again variation occured in 2004 (t = -3.337,P = 0.002).We found no differences on richness among years (F 3,219 = 1.200,P = 0.311), between times of day (F 1,219 = 3.752, P = 0.054) and in the interaction between different years and times of day (F 3,219 = 2.491, P = 0.061) (Fig. 3 and Table 1).
Considering all the environments sampled, the families with the highest richness were Tyrannidae and Psittacidae, with 32 and 16 species, respectively, followed by Columbidae, Picidae and Emberizidae, each with 13 species.Twenty-five families were represented by only one or two species.The highest species richness of Tyrannidae (Passeriformes) and Psittacidae (non-Passeriformes) was recorded in the savannah, forested savannah and gallery forests.In the grasslands, more species of Emberezidae were registered.Ardeidae and Threskiornithidae were dominant in number of species in salinas, in the bays and in the river.Momotidae was restricted to the gallery forest, Alcedinidae standing out in the river and bays.Some tyrannids were restricted to one  Abundance: Total abundance of birds was not different among years (F 3,219 = 1.999,P = 0.115), times of day (F 1,219 = 2.066, P = 0.152) and between times of day when it was dependent upon the years (F 3,219 = 0.252, P = 0.680).However, it showed significant variation in the interaction between years and seasons (F 3,219 = 3.685, P = 0.013) since 2004 showed significant differences in abundance between both seasons (t = -3.224,P = 0.002).Thus, it could be said that the dry season would attract more visiting birds to better exploit the resources in aquatic environments (rivers, bays, and salines) when the water level drops in these environments.On the other hand, the rain would delay this process, allowing the birds to be less concentrated in these aquatic environments.Another relevant factor in relation to the dry season is that many species of aquatic visiting birds nest on the edges of aquatic environments and food is more easily obtained with the decrease of water.
Total abundance of birds was different among years (F 3,219 = 6.549,P < 0.001), among habitats (F 6,219 = 32.798,P < 0.001) and in the interaction between different years and habitats (F 17,219 = 3.115, P < 0.001).The post-hoc Tukey test showed two major groups: one composed by habitats with low abundance, such as grasslands, forested savannah, savannah, bays and riparian forests, and another one formed by salines and river, that have higher abundance (Fig. 4 and Table 2).
Psittacidae was the most abundant family in the region, with prominence in all environments.Recurvirostridae, a monospecific family, showed expressive abundance due to the dominance of Himantopus mexicanus in the salinas, followed by Ardeidae, Anatidae and Cracidae.Other families with high abundance were Tyrannidae, Columbidae, Thraupidae and Emberizidae, all in predominantly terrestrial environments.Among the most abundant species we registered Brotogeris chiriri standing out in all the sampled environments.Other species with great abundance in the different environments were Ortalis canicollis, Amazona aestiva, Dendrocygna viduata, Cantorchilus leucotis and Pitangus sulphuratus.The 30 most  abundant species together represented 61 % of all records.Dendrocygna autumnalis was preferentially concentrated in the rivers and salines while Cairina moschata was frequently distributed in the bays.Anhinga anhinga and Nannopterum brasilianus were recorded almost exclusively in the river, except for some records of the second in the bays and salines.The Ardeidae were more frequent in the river, followed by the salines and expressively less common in the bays.Treskiornithidae were more frequent in the salinas while the Ciconiidae stood out in the river.The distribution of limnic species was heterogeneous among the three aquatic environments.Vanellus chilensis (N = 206), H. mexicanus (N = 1712), Tringa flavipes (N = 241), T. melanoleuca (N = 149) and Phaetusa simplex (N = 197) were abundant in the salines.Jacana jacana (N = 210) was abundant in bays, salines and grasslands.P. simplex was abundant in saline and common in the river, while S. superciliary and Chlidonias niger (N = 130) had ample abundance only in the river.
Migratory species: A total of 98 species of migratory birds were registered in Pantanal of Rio Negro (Appendix 1).The vast majority of migratory species were recorded between June and September.The following were exceptions: Crotophaga major, a summer migratory species recorded only during the wet season; Anhinga anhinga, normally recorded in large numbers during summer (small numbers in winter); Nannopterum brasilianus, present in summer and the early dry season (winter in the Pantanal); and Phaetusa simplex (Gmelin, 1789), another species that migrates in summer.There is also Hirundo rustica Linnaeus, 1758, seen usually in large flocks during summer (wet season).Those typical of the rainy period (summer), with more than 100 recordings were N. brasilianus, P. simplex, Tachybaptus dominicus, C. major and Mesembrinibis cayennensis (Gmelin, 1789).At some time, any of these species can be recorded in small numbers in different seasons.DISCUSSION Naumburg (1930) was one of the pioneers in describing birds of the Pantanal, followed by Mitchell (1957).Cintra and Yamashita (1990) went a step further and described the habitats, distribution, and abundance of bird species in the Northern Pantanal.Brown (1986) analyzed the distribution and biogeographic affinities of over 650 bird species in the Pantanal.Dubs (1992) presented a catalogue of birds from Southwestern Brazil and bordering regions in the Pantanal region with almost 700 species of birds.The avifauna from Pantanal wetlands has the highest species richness among the wet areas in the World, sheltering approximately 460 species (Nunes & Thomas, 2004a).Moreover, new species are added every year to the Pantanal list (Nunes et al., 2008).Figueira et al. (2006) found more bird species richness in forest areas, followed by savannahs and grasslands and floodable or aquatic fields.In terms of aquatic habitats, the diversity of bird community in the dry season varies significantly in the salines, followed by the bays and more stable in the Negro river.The Negro river, regardless of large annual amplitude of flow, is more seasonally stable since its riparian vegetation is continuous (not isolated) and constant (Donatelli et al., 2014).Our results showed the same pattern recorded by these authors in relation to aquatic habitats but this work, the first of its kind, will be a reference for further studies of birds in Pantanal, for various fields of research.
The temporal and spatial variation in the abundance of birds in the tropics has already been highlighted by several authors (Blake & Loiselle, 1991) and the fluctuations in bird abundance are already known in Pantanal (Nunes & Thomas, 2004a).Thus, as registered in the present work, in the dry season the abundance of birds was higher than in the wet period.The dry season is related to high availability of food and decrease in the volume of water in the wetland system (Por, 1995).On the other hand, Poulin, Lefebvre and McNeil (1993) registered lower abundances of birds at the beginning of the reproductive period in deciduous and dry forests in Venezuela, associating this to the low availability of food.
The spatial distribution of the animal diversity has also been explained in climate and vegetational structure (Cueto & Casenave, 1999;Veech & Crist, 2007).According to Farley, Ellis, Stuart & Scott (2004) habitat variability is a determinant part of the structure and dynamics of a community of birds, because most of the species are closely related to specific habitats.We found that there was no significant variation in the abundance of birds in the same habitat in four years of data collection, but a great significant variation between different habitats was observed; this fact was expected, considering the peculiar characteristics of each habitat.So, in a regional scale, the factors that seem to influence bird abundance are habitat type, size, and diversity of habitats existing in a specific place (Rafe, Usher, & Jefferson, 1985), being the heterogeneity of habitats a predominant factor in the determination of the number of birds' species (Rafe et al., 1985;Farley et al., 1994;Bailey et al., 2004;Blake, 2007).Figueira et al. (2006) found more bird species richness in forest areas, followed by savannahs and grasslands and floodable or aquatic fields.On the other hand, in terms of abundance, we observed that the open habitats, such as the salines and rivers had a higher abundance of birds than the other habitats (categorized as closed); a possible reason for this was a large concentration of species of shorebirds exploring food in these environments.Figueira et al. (2006) analysed bird diversity of Pantanal wetlands in Mato Grosso and found three types of habitats with similar diversity: 1) forested habitats (forested savannah and riparian forests); 2) savannah (savannah sensu strict and grasslands); and 3) aquatic habitats (rivers, bays, corixos).Species which share distinct habitats may also indicate, indirectly, the potential flow of individuals and species among the different habitats and consequently, the complexity, the interconnectivity and the flexibility of interactions in the food chain.Thus, the heterogeneity of habitats is fundamental for the maintenance of the diversity of both aquatic and terrestrial birds (Figueira et al., 2006).On the other hand, our results also indicated that it seems quite remote that Pantanal wetlands share bird species with other habitat, except in particular conditions (river and riparian forests, salines and rivers).Results of abundance showed specificity and each habitat has its own importance in the whole context, notwithstanding the sharing of habitats.
Considering migratory species, Nunes and Tomas (2004b) listed 133 species of migratory birds with occurrence in the plains of the Pantanal wetlands.In this study 98 species, approximately 74 % of all the migratory birds that occur in the plains of the Pantanal were registered.According to the reference chart from these authors, we have the following profile regarding the migratory birds in the Pantanal do Rio Negro: 1) Most of these species have aquatic habits; 2) approximately 40 % are migrant from the American continent, and 32 % from national territory; 3) approximately 15 % come from Central America, North of South America and North America and 13 % from the extreme South of South America; 4) None of them has been considered in situation that requires attention regarding conservation and 5) the vast majority has got unknown destination.
The results highlight some important issues regarding the abundance of birds in this region of Pantanal wetlands: a) The morning period and the dry season register the highest number of birds, regardless of the habitat; b) there are no significant differences in abundance in the same habitat along the years, but the habitats among themselves showed different total abundances.
In general, the results indicated that there is a relatively stable abundance in each habitat along years, but there is a clear difference in abundance among the habitats yearly, associated with their particularities.Pantanal of Rio Negro is an enormous complex of interconnected habitats on which the local community of birds depends.This diversity of habitats contributes to the high abundances recorded, as well as to the biome as a whole.Thus, additional studies on food availability in dry and wet seasons should be better explored in the future, either in this region or in other Pantanal regions.This fact could better explain the seasonal dynamics of the richness and abundance of birds in the Pantanal in general.

ACKNOWLEDGMENTS
We must acknowledge our immense debt to Earthwatch Institute for the opportunity to carry out the ornithological research Project in the Pantanal, and to the more than 300 volunteers who assisted us in the field from 2001 to 2004.Heartfelt thanks to Conservation International for logistic support at Fazenda Rio Negro.We also want to thank Alexine Keuroghlian and Don Eaton for their invaluable support in Campo Grande and at Fazenda Rio Negro; to Jeff Himmelstein for his assistance at all times and also for friendship.We are grateful to all staff at the Fazenda (Geni, Baiano, Celso, Seu Japão, Picolé, and Ico).We thank very much the reviewers of the manuscript who made valuable suggestions.
or two environments, such as Cnemotriccus fuscatus and Lessonia rufa in the forested savannah, Gubernetes yetapa, Camptostoma obsoletum and Megarynchus pitangua in the savannah, Xolmis velatus in the grasslands, Philohydor lictor in the river and Machetornis rixosa in the salinas.Pitangus sulphuratus, on the other hand, was well distributed in the all environments.

TABLE 1
Richness of birds in the Pantanal for times of day and seasons between 2001 and 2004

TABLE 2
Abundance of birds in the Pantanal for times of day and seasons between 2001 and 2004