The Sapphire-spangled Emerald Amazilia lactea complex is currently represented by three subspecies with disjunct geographical ranges. A. l. bartletti occurs over a limited portion of south-western Amazonia in Brazil, south-east Peru and northern Bolivia, and is a very little-known taxon in nature. We present data on the breeding and biometrics of this race based on six nests found between 1999 and 2019, and 58 adult individuals captured between 2010 and 2018 in eastern Acre state, Brazil. The nest of A. l. bartletti is a low cup / base type, constructed primarily of kapok wool and decorated with lichens on the outer walls. The nestling period was estimated at 18–20 days. Our data indicate that A. l. bartletti breeds from at least December until March.
Sapphire-spangled Emerald Amazilia lactea comprises three subspecies with markedly disjunct geographical distributions: A. l. lactea in south-east Brazil, from Santa Catarina north to Bahia; A. l. zimmeri in south-east Venezuela; and A. l. bartletti in south-west Amazonian Brazil, adjacent south-east Peru and northern Bolivia (Zimmer 1950, Weller et al. 2020). Based on plumage and morphometrics, the Handbook of the birds of the world currently treats bartletti at species rank, Spot-vented Emerald A. bartletti (del Hoyo & Collar 2014). However, for the purposes of this study we follow the taxonomy and nomenclature of Piacentini et al. (2015), who considered this taxon as a subspecies of A. lactea.
Sapphire-spangled Emerald inhabits the edges of primary forest, as well as secondary forest, plantations, and urban environments. Almost all of the available breeding data for this species pertain to A. l. lactea (Oniki et al. 2000, Weller et al. 2020). To augment our knowledge of reproduction and biometrics of the race A. l. bartletti, we present data on the nest, nestlings, morphometry, and mass of this race from observations made in eastern Acre state, in south-west Brazilian Amazonia.
Study area.—Nests reported here were found during non-systematic observations made between 1999 and 2019 at the Campus and Zoobotanical Park of the Universidade Federal do Acre (UFAC) (09°57′03.22″S, 67°52′30.65″W), Rio Branco, while adults were captured, measured and banded annually there in 2010–18. A description of the habitats and avifauna of the study area can be found in Guilherme (2001).
Nests.—Inactive A. l. bartletti nests were collected and deposited in the nest collection of the ornithology laboratory at UFAC (Table 1). Measurements of these nests were taken using digital callipers.
Capture, marking and biometrics.—During 2010 to 2018, 58 adults were trapped using mist-nets, 12 m long and 2.5 m high with a 36-mm mesh. Capture effort was c.4,000 net / hours / year. Birds were marked 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). We weighed adults and nestlings using a Pesola® balance with 100 g capacity and 1 g precision in 2010–14, and a digital scale (0.05 g precision) in 2015–18. We collected standard morphometric data (wing length flattened, bill length from the tip to the feathers, and total length) following the protocol outlined by Proctor & Lynch (1993). To measure wing and total length we used a ruler with a millimeter scale, while to measure bill length we used analogue callipers (0.05 mm precision) in 2010–14, and digital callipers (0.01 mm precision) in 2015–18.
Measurements (mm) of Sapphire-spangled Emerald Amazilia lactea bartletti nests held in the ornithology laboratory of the Universidade Federal do Acre (UFAC), Rio Branco, Brazil.
Nests and nestlings.—Six nests of A. l. bartletti were found between 1999 and 2019 (Table 2; Figs. 1A, 1F, 2A). Of these, four were active when discovered and two inactive (Table 2). Four of the six had the support plant identified to genus or species (Table 2). Measurements, means and standard deviation of the parameters for three of the six nests are presented in Table 1.
The nests, of the low cup / base type (sensu Simon & Pacheco 2005), were sited on horizontal branches and comprised cotton-like fluff (kapok) obtained from seeds of Ceiba sp. or Ochroma sp. The outer walls of the nests were lichen-decorated (Figs. 1A, B, F, 2A, B, E).
Nestlings hatch virtually featherless (Fig. 2C–D), with two lines of down on the dorsal spinal tract (sensu Lucas & Stettenheim 1972; Fig. 2C). They have dark skin on the dorsal and lateral surfaces, closed eyes and an orange bill (Fig. 2C–D).
Nest 2.—When it was found on 21 February 2013, this nest contained two recently hatched nestlings (Fig. 1 A–B). It was constructed on the branch of a mango tree c.2 m above ground (Table 2). The nest was monitored for 18 days until the nestlings fledged. During this period, they were fed by just one adult, presumably the female, which collected nectar from flowers of native and exotic species near the laboratory blocks and campus classrooms (Fig. 1C–E) including Costus sp., Hibiscus rosa-sinensis and Monotagma sp. (Fig. 1C–E). On 9 March 2013, the nestlings, already feathered and mass 5 g, were banded (code A07384 and A07400). On 10 March 2013 the young were seen perched on branches near the nest, but still being fed by the female. The minimum nestling period was therefore 17 days.
Nests of Sapphire-spangled Emerald Amazilia lactea bartletti found in the Campus and Zoobotanical Park of the Universidade Federal do Acre, Rio Branco, Brazil, between 1999 and 2019.
Nest 4.—This nest was found on 23 March 2017, also with two recently hatched nestlings. The nest was constructed on a branch of an exotic Tectona grandis plant, c.1.8 m above ground (Table 2; Fig. 2A, B, E). On the day of discovery, the nestlings weighed 2.2 g and 1.6 g, respectively. On 4 April 2019, 12 days later, we banded and measured the nestlings. As we approached, one of the nestlings flew to the edge of the forest and was not seen again. The other was banded (code A 62933) and weighed 4.69 g. Morphometrics taken from this nestling were: bill 11 mm; wing 33 mm and total length 65 mm. Next day, this nestling was also not present near the nest.
Morphometrics.—Fifty-eight adult A. l. bartletti were trapped and measured between 2010 and 2018. The mean and standard deviation of the measured parameters were: bill 20.7 ± 1.5 (range 17–25 mm, n = 51); wing 53.2 ± 3 (41–61 mm, n = 58); tail 29.7 ± 2.5 (25–35 mm, n = 58); total length 92.5 ± 5.8 (86–106 mm, n = 49) and mass 4.7 ± 0.6 (3–6 g, n = 58).
The first record of A. l. bartletti in Brazil involved a female collected in 1951 in the vicinity of Rio Branco, the capital of Acre (Pinto & Camargo 1954; Museu de Zoologia da Universidade de São Paulo, MZUSP 35630). In Acre, A. l. bartletti is one of the commonest hummingbirds, being present in forest fragments (mainly at their edges), farms, and squares and gardens in cities (Guilherme 2016).
There is just one reference to an A. l. bartletti nest found in Bolivia (del Hoyo et al. 2019), whereas all other known breeding information for Amazilia lactea refers to the south-eastern South American race A. l. lactea (Ihering 1900, Ruschi 1986, Oniki et al. 2000, Weller et al. 2020). Thus the nests reported here represent the first detailed information for A. l. bartletti (del Hoyo et al. 2019).
The shallow cup-shaped nest constructed of kapok fibres is similar to that described for A. l. lactea (Ihering 1900, Oniki et al. 2000). The kapok used (Fig. 2B) probably came from the fruits of Ceiba lupuna or Ochroma pyramidale, which are common tree species in the UFAC Campus and Zoobotanical Park. As noted by Oniki et al. (2000), the presence of bark strips or thin twigs in the outer wall is low and, in some nests, practically non-existent. Mean measurements of the nests of A. l. bartletti are consistent with those of A. l. lactea reported by Ihering (1900) and Oniki et al. (2000).
Nests of A. l. bartletti are decorated with lichens like those of A. l. lactea (Oniki et al. 2000), Copper-rumped Hummingbird A. tobaci (Muir & Butler 1925), Rufous-tailed Hummingbird A. tzacatl (Skutch 1931), Glittering-throated Emerald A. fimbriata (Haverschmidt 1952) and Azure-crowned Hummingbird A. cyanocephala (Ornelas 2010). Decorating the outer walls of the nests with lichens is primarily a camouflage strategy (McCormac & Showman 2010).
We estimate the nestling period as between 18 and 20 days, based on nest 2 which contained two recently hatched nestlings and was followed until they fledged 17 days later. We believe that the nestlings hatched at least two or three days prior to the nest's discovery. According to Oniki et al. (2000), the nestling period of A. lactea may be no longer than 20 days, i.e. slightly shorter than the 22 days reported by Ruschi (1986) and Weller et al. (2020) for A. l. lactea. The literature indicates that in other species of Amazilia the nestling period varies from 18 to 23 days (Fierro-Calderón & Martin 2007). Skutch (1931) reported that young Rufous-tailed Hummingbirds left the nest when 21 days old, Glittering-throated Emerald at 20 days (Haverschmidt 1952) and young Copper-rumped Hummingbirds when 19–23 days old (Muir & Butler 1925, Baird 2017).
Nestlings of A. l. bartletti are black-skinned dorsally, and pink on the belly, while the bill and mouth-lining are yellow / orange, just as described for Glittering-throated Emerald (Haverschmidt 1952) and similar to Azure-crowned Hummingbird (Ornelas 2010). The mass at fledging is presented here for the first time, and is close to mean adult weight, indicating that young only leave the nest when they achieve adult mass. Glittering-throated Emerald young also leave the nest when they reach c.5 g (Haverschmidt 1952). However, nestlings fledge when their bill is slightly smaller than that of the adult, as also observed in Glittering-throated Emerald (Haverschmidt 1952).
Foraging data for A. l. bartletti is virtually non-existent (del Hoyo et al. 2019). Our observations indicate that like A. l. lactea (Oniki et al. 2000), A. l. bartletti feeds its nestlings with nectar from native and exotic plants growing in open areas and gardens near the nest. From the dates of the active nests we found (Table 1) it appears that A. l. bartletti breeds in south-western Amazonia from at least December until March.
We are grateful to CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and UFAC for providing JML and EAS with an undergraduate research stipend. We are grateful to all the members of the research team of the UFAC ornithology laboratory for their support during field work and to the Centro Nacional de Pesquisa e Conservação de Aves Silvestres (CEMAVE / ICMBio), for providing the bands used in project 1099. We also thank the anonymous reviewers for their comments and suggestions.