Humaitá Forest Reserve (HFR) is a forest fragment in the state of Acre, Brazil. Between 2009 and 2019, this fragment has been inventoried by multiple ornithologists and birdwatchers. To provide a comprehensive list of the avifauna of HFR, we compiled all of the available data, including published reports and recent, unpublished surveys. The list includes 356 bird species belonging to 60 families and 23 orders. This species richness is the greatest recorded in those forest fragments that have been inventoried in eastern Acre. We found that HFR is an important site for the conservation of many threatened species, and migrants, as well as poorly known species with a restricted geographic distribution, such as Semi-collared Puffbird Malacoptila semicincta, Goeldi's Antbird Akletos goeldii, Rufous Twistwing Cnipodectes superrufus and Acre Tody-Tyrant Hemitriccus cohnhafti.
South-west Amazonia is one of the world's biologically richest regions in terms of birds, with more than 500 species at some localities (e.g. Terborgh et al. 1984, Parker et al. 1994, Brown & Freitas 2002, Whittaker et al. 2002). The avifauna of the Brazilian state of Acre, which borders Peru, Bolivia and the Brazilian states of Rondônia and Amazonas, is well known, with more than 700 species documented (Guilherme 2016). In addition to species richness, the region is also characterised by high endemism, with many species unique to the Inambari centre of endemism between the Solimões and Madeira Rivers (Haffer 1978, Cracraft 1985, Silva et al. 2019). In Acre, at least 23 species are confined to the Inambari centre, and 12 of these occur in Brazil only in Acre and adjacent parts of Amazonas (Guilherme 2012, 2016). Furthermore, some species are restricted to eastern Acre, including many bamboo specialists (Guilherme & Santos 2009, Guilherme 2012, 2016).
Eastern Acre is also the region most affected by anthropogenic impacts in south-west Amazonia, at the western extreme of the ‘Arc of Deforestation’ in southern Amazonia, where cattle-ranching and cash-cropping are expanding relentlessly (Fearnside 2017). Acre's capital, Rio Branco, is also in this region, which is characterised by a mosaic of many urban and rural forest fragments within an anthropogenic matrix dominated by cattle pasture (Guilherme 2016).
Fragmentation of forest not only impacts avian communities, in particular by eliminating certain ecological guilds (Stouffer & Bierregaard 1995, Bierregaard & Stouffer 1997, Stratford & Stouffer 1999), but may also affect the physiological integrity of individual birds (Hernández-Palma & Stouffer 2018). Long-term studies of bird communities in forest fragments may provide potentially valuable insights into the impacts of fragmentation on community structure vis-à-vis pristine habitats (Rutt et al. 2017).
Although the number of bird surveys has progressively increased in Amazonia, systematic long-term surveys of a given area are still rare (Rutt et al. 2017). We compiled a list of the avifauna of Humaitá Forest Reserve (HFR), a forest fragment owned by the Instituto Nacional de Colonização e Reforma Agrária (INCRA), but which has been ceded to the Universidade Federal do Acre (UFAC) for research purposes. Other inventories available for HFR include medium-sized and large mammals (Botelho et al. 2012) and palms (Pinheiro et al. 2015). In 2009, the ornithological database of the HFR was consolidated during doctoral research by EG (Guilherme 2009). Since then, further work has been conducted in HFR, including by TLS and colleagues (Silva et al. 2015), TNM & EG (Melo & Guilherme 2016), DP & EG (Pedroza & Guilherme 2019) and JL and colleagues (Lima et al. 2019). While ongoing research in HFR over the past ten years has produced an increasingly solid database on its avifauna, no comprehensive list of birds was available for the reserve, until the present study.
Study area.—Humaitá Forest Reserve (HFR) is in the municipality of Porto Acre (09°45′52″S, 67°38′02″W), Acre, Brazil (Fig. 1), and covers c.2,000 ha (Botelho et al. 2012). The fragment is surrounded by the Humaitá Settlement Project and farms, with the Acre River forming its eastern limit. Climate is tropical humid, with mean annual temperatures of 24–26°C (Alvares et al. 2013) and mean annual rainfall of 1,900 mm (Alvares et al. 2013). Vegetation is a mosaic of open forest with bamboo, and open forest with palms on terra firme and seasonally flooded (várzea) soils (Barroso et al. 2011).
Data collection.—The preliminary bird species list for HFR was based on three published inventories (Guilherme 2009, 2016, Silva et al. 2015). We added unpublished records by other observers, together with those on digital platforms such as Wikiaves and Xeno-canto. Registration numbers of records on Wikiaves (WA) and Xeno-canto are indicated in the species accounts and Appendix. Species were identified via captures in mist-nets, visual observations or their vocalisations. Specimens collected in HFR and deposited in the ornithology laboratory at UFAC, Rio Branco, and the Museu Paraense Emílio Goeldi (MPEG), Belém, were also examined. Voucher specimens and media identification numbers published online were considered as physical evidence of the species' occurrence in HFR.
Species classification.—The list was reviewed to identify migratory, endemic species, habitat specialists, cynegetic and threatened species. Migratory species were classified using Somenzari et al. (2018), while bamboo forest specialists and species associated with patches of Guadua bamboo were identified based on Kratter (1997), Guilherme & Santos (2009), Lebbin (2013) and Guilherme (2012, 2016). Species endemic to the Inambari centre of endemism (sensu Silva et al. 2005, 2019) were identified using Haffer (1978), Cracraft (1985) and Guilherme (2012, 2016). Game (cynegetic) species targeted by subsistence hunters were classified following Ojasti (1993), Sick (1993) and Sigrist (2014). Conservation status follows IUCN (2019).
Feeding guild and foraging stratum of each species was also determined, based on Wilman et al. (2014). Scientific nomenclature follows that of the Comitê Brasileiro de Registros Ornitológicos (Piacentini et al. 2015). In some cases, voucher specimens were collected under ICMBio / SISBio authorisation no. 23269-1, and deposited either at UFAC, Rio Branco, or MPEG, Belém. Some birds were banded using numbered metal rings supplied by CEMAVE (Centro Nacional de Pesquisa e Conservação de Aves Silvestres), under the scope of project 1099, coordinated by EG (senior bird bander, reg. no. 324654).
Compilation of records made in HFR between 2009 and October 2019 revealed the presence of 356 bird species in 60 families and 23 orders (Appendix). Families represented by the largest numbers of species were Thamnophilidae (n = 37 species, 10.3% of the total), Thraupidae (n = 28 species, 7.9%), Tyrannidae (n = 26 species, 7.3%), Rhynchocyclidae (n = 17 species, 4.8%) and Psittacidae (n = 14 species, 3.9%). Overall, 195 species (54.8%) are passerines and 161 (45.2%) non-passerines.
The most species-diverse foraging guilds (Appendix) were the insectivores (196 species), frugivores (56 species) and omnivores (42 species). Most birds forage in the midstorey (84 species), canopy (50 species) or alternate between the understorey and midstorey (40 species).
Thirteen bird species visit HFR on migration (Fig. 2). Slightly more than half of these (53.8%, n = 7) are austral migrants, with the remainder 23.1% (n = 3) being intra-tropical migrants and 23.1% (n = 3) Nearctic migrants. Eleven species (3.1%) are endemic to the Inambari centre of endemism. Eighteen species (5.04%) are either bamboo forest specialists or possess some degree of association with tracts of Guadua bamboo in south-west Amazonia (Fig. 3). Twenty-nine species (8.1%) are considered to be cynegetic (Appendix), including Tinamidae (n = 9 species, 2.5% of the total), Anatidae (n = 1 species, 0.3%) and Cracidae (n = 3 species, 0.8%). Sixteen (4.5%) species are included in higher categories of threat by the IUCN (2019), including nine Near Threatened (2.5%) and seven Vulnerable (2%) (Appendix). Below, we comment on aspects of the biology and distribution of selected species.
BROAD-WINGED HAWK Buteo platypterus
Nearctic migrant. Observed by DP at the edge of HFR on 9 November 2017 (WA2792378; Fig. 2A). Only the second record in Acre (Guilherme 2016). Stotz et al. (1992) reported the species' occurrence in neighbouring Rondônia between October and March. This indicates that the record at HFR was within its overwintering period in south-west Amazonia.
ASH-COLOURED CUCKOO Micrococcyx cinereus
Austral migrant. Guilherme (2009) first reported the species in HFR. A female, collected on 20 July 2007, is deposited in Belém (MPEG 63485). The date of this record corresponds to the coldest part of the austral winter in southern Brazil, where the species breeds (Payne 2019a).
YELLOW-BILLED CUCKOO Coccyzus americanus
Nearctic migrant. One observed by DPG foraging for insects in the canopy on 30 October 2017 (WA3515980; Fig. 2B). Breeds in North and Middle America, and migrates to South America in the boreal winter (Payne 2019b). The date of this record indicates that C. americanus arrives in the region shortly before the start of the boreal winter. Only the third record in Acre (GBIF 2019, Wikiaves 2019).
RUFOUS-HEADED WOODPECKER Celeus spectabilis
Bamboo forest specialist. Common in HFR, where invariably observed in bamboo. The territorial song and drumming is audible over long distances, and evidence of its feeding behaviour is often observed on bamboo stalks. A pair with two juveniles observed by TNM on 12 August 2014, in bamboo near the reserve headquarters (Fig. 3A).
BLUISH-SLATE ANTSHRIKE Thamnomanes schistogynus
Endemic. Guilherme (2009) presented the first records in HFR. Specimens have been deposited in Belém (MPEG 59967, 59968). Subsequently, in 2018, DPG monitored the species. He found that T. schistogynus is a mixed-species flock leader in HFR, and occurs in bamboo forest and terra firme forest with palms.
YELLOW-BREASTED WARBLING ANTBIRD Hypocnemis subflava
Endemic; bamboo forest specialist. Silva et al. (2015) made the first record in HFR, and DP monitored the species in 2017. In HFR, the species occurs exclusively in bamboo forest, foraging for prey in bamboo culms and leaves. Population density was estimated in 16-ha grids, with some individuals being banded, at 0.55–0.66 pairs per ha in bamboo patches (Pedroza & Guilherme 2019). In DPG's 2018 study of mixed-species flocks, H. subflava was a constant presence in flocks led by Thamnomanes schistogynus and the flock's home range coincided with bamboo patches.
RUFOUS TWISTWING Cnipodectes superrufus
Endemic; bamboo forest specialist; Vulnerable. In August–September 2014, TNM observed one in bamboo patches near the reserve headquarters; see Melo et al. (2015) (Fig. 3B). On 5 June 2018, DPG trapped and ringed (CEMAVE F55386) one in a bamboo patch, and on 1 August 2018, JML trapped and ringed a second individual (CEMAVE F63509) in a part of the forest apparently without any major concentration of Guadua bamboo, whereas the species typically occurs in patches of dense bamboo (Tobias et al. 2008). HFR is the northernmost locality at which C. superrufus has been recorded (Melo et al. 2015, Guilherme 2016).
ACRE TODY-TYRANT Hemitriccus cohnhafti
Endemic; bamboo forest specialist; Near Threatened. Recently described species for which few natural history data are available (Zimmer et al. 2013, Melo et al. 2015). One was recorded in a bamboo patch at HFR on 19 November 2018, by R. Plácido (WA2376966) (Fig. 3C). The record extends the species' known range 95 km north of the nearest previously known locality, on the Transacreana highway in Acre (Melo et al. 2015).
LARGE-HEADED FLATBILL Ramphotrigon megacephalum
Bamboo forest specialist. Silva et al. (2015) first recorded this species in HFR, and TNM subsequently studied its foraging behaviour, which is focused exclusively on bamboo leaves and branches (Melo & Guilherme 2016). Density of R. megacephalum along a 10-km transect in the study area was estimated 1.5 individuals/km2, with the species being exclusively recorded in areas of bamboo. In the 2018 study of mixed-species flocks, DPG considered R. megacephalum to be a constant in flocks led by Thamnomanes schistogynus.
DUSKY-TAILED FLATBILL Ramphotrigon fuscicauda
Species associated with bamboos. Guilherme (2009) was the first observer to record R. fuscicauda in HFR. Ecologically more flexible than R. megacephalum, it occurs in both bamboo-dominated habitats and areas without bamboo, although it is commonly found on bamboo, and is observed foraging close to R. megacephalum (Melo & Guilherme 2016). Density of R. fuscicauda along a 10-km transect in HFR was estimated at 0.8 individuals/km2. DPG considered this species to be another constant participant in mixed-species flocks led by Thamnomanes schistogynus.
Bird species richness recorded in HFR (356 species) corresponds to 50.4% of the 708 species currently documented in the state of Acre (Guilherme 2016). This is an impressive number of species, considering that the fragment covers just 2,000 ha. The number of bird species recorded in HFR has progressively increased since 2009, when just 120 species had been recorded in the area based solely on specimens in museums (Guilherme 2009). The increase is due to constant ornithological field work in this forest, together with sporadic visits by amateur birdwatchers in the last ten years. Surveys in HFR prior to 2019 indicate that the site has a similar bird species richness to that in areas of continuous forest inventoried in Acre during shorter term studies, including Rio Acre Ecological Station (Guilherme & Aleixo 2010) and Chico Mendes Extractive Reserve (Mestre et al. 2010). Bird species richness in HFR is also considerably greater than that recorded in isolated fragments inventoried over the long term, e.g., Catuaba Experimental Farm (Rasmussen et al. 2005) (c.36 km from HFR) and the UFAC Zoobotanical Park (Guilherme 2001, 2016) (c.31 km from HFR).
Both of these sites are in eastern Acre and administered by UFAC. Prior to 2001, 150 bird species had been recorded in the Zoobotanical Park (Guilherme 2001), an area of c.100 ha (Meneses-Filho 1995), although this total increased to 196 species over the next 15 years (Guilherme 2016). In the Catuaba Experimental Farm fragment of 1,200 ha (Medeiros et al. 2013), 257 bird species were recorded by Rasmussen et al. (2005), and this number rose to 275 over the next 11 years (Guilherme 2016). Despite the increasing inventory, total richness at both sites is still lower than at HFR. The Zoobotanical Park is a small fragment within an urban matrix and has virtually no connectivity to other forested areas (Guilherme 2001), whereas Catuaba Experimental Farm is much larger, located within a rural matrix, and surrounded by properties with private reserves of forest (as mandated under current Brazilian environmental legislation). In contrast to these sites, HFR is a much larger area of forest, relatively distant from populated areas, and lies within a matrix of pasture and numerous private forest reserves that together with HFR form a single fragment. Although these areas are not directly comparable due to differences in the size and configuration of the fragments, their history of isolation and characteristics of the matrix (Ferraz et al. 2007), the progressive increase in number of species recorded at each site over time indicates that additional species will be recorded in HFR by further surveys.
Approximately 5% of bird species in HFR are associated with bamboo forests of south-west Amazonia (Kratter 1997, Guilherme & Santos 2009, Guilherme 2012, 2016). These species include two of the rarest birds at HFR, Rufous Twistwing and Acre Tody-Tyrant (Tobias et al. 2008, Zimmer et al. 2013, Harvey et al. 2014, Melo et al. 2015). The presence of ecological guilds most sensitive to fragmentation, such as mixed-species flocks of understorey insectivores, terrestrial insectivores and army ant followers, reflects the conservation potential of HFR for birds. The presence of several gamebirds, especially Razor-billed Curassow Pauxi tuberosa, Spix's Guan Penelope jacquacu and large tinamids such as Grey Tinamus tao and Great Tinamous T. major, indicates the viability of their local populations, despite hunting (DP & TNM pers. obs.). These findings are similar to those of Botelho et al. (2012) for medium and large mammals in HFR. Although they tend to become rarer, large cracids appear to be able to persist in areas with moderate hunting pressure (Barrio 2011, Kattan et al. 2016). The presence of Crested Morphnus guianensis and Harpy Eagles Harpia harpyja, which are also targeted by hunters (Trinca et al. 2007, Muñiz-López 2017) is a further indication of the favourable conditions. HFR is almost completely surrounded by cattle pastures, which environment lacks resources for the majority of migratory birds (Saab & Petit 1992), making HFR an important site for migratory species from different regions of the Americas during the year.
HFR is a potentially important area for bird conservation in eastern Acre, given that it has the highest bird species richness recorded anywhere in the state. In addition, it harbours important endemics and habitat specialists, and serves as a strategic stopover for migratory species. Birdwatching, which was initiated in 2013 at HFR by TNM, has attracted people from elsewhere in Brazil and other countries. This type of sustainable tourism has the potential to yield important economic benefits for the region. The proximity to the capital, Rio Branco, and the presence of rare birds such as Ash-throated Gnateater Conopophaga peruviana, Cnipodectes superrufus and Hemitriccus cohnhafti, should attract growing numbers of birders, who in turn can continue to monitor bird populations and add new species to the site list. Some rare species, such as Morphnus guianensis, were already found at HFR by hobby birders. Supervision by competent authorities (e.g., Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renováveis - IBAMA) of this important reserve and continued monitoring of its avifauna should guarantee its role as a safe haven for the biodiversity of a region under increasing anthropogenic pressure.
We thank the Universidade Federal do Acre via the graduate faculty and Programa de Pós-Graduação em Ecologia e Manejo de Recursos Naturais (MECO) for logistical support during our surveys. We also thank Ricardo Plácido for providing the photo of H. cohnhafti. DP, TNM & JML were funded by scholarships from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and DPG & TLS by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). EG is grateful to the Centro Nacional de Pesquisa e Conservação de Aves Silvestres (CEMAVE / ICMBio), for providing the bird bands used in project 1099.
Bird species recorded in the Humaitá Forest Reserve between 2009 and 2019, in Acre, Brazil. Guilds: FR = frugivore; INS = insectivore; INV = invertebrates; NEC = nectarivore; O = omnivore; PS = granivore; VS = vertebrate scavenger. Strata: AE = aerial; W = water; C = canopy; G = ground; G/C = ground/canopy; G/ UND/MID = ground/understorey/mid-high; G/UND = ground/understorey; MID = mid-high; MID/C = mid-high/canopy; MID/C/AE = mid-high/canopy/aerial; UND = understorey; UND/AE = understorey/aerial; UND/MID = understorey/mid-high; UND/MID/C = understorey/mid-high/canopy. Conservation status: * = Near Threatened, ** = Vulnerable. Ecological characteristics (see first column): B = Bamboo forest specialist or associated with bamboo, NM = Nearctic migrant; AM = austral migrant; IM = intra-tropical migrant; E = endemic; C = cynegetic (gamebird). Voucher: MPEG = Museu Paraense Emílio Goeldi, Belém; AC = ornithology laboratory at Universidade Federal do Acre; WA = Wikiaves; XC = Xeno-canto; CEMAVE = ringed.