Sclerurus is a monophyletic group (Derryberry et al. 2011) comprising six to eight species according to different authorities (del Hoyo & Collar 2016, Billerman et al. 2020, Remsen et al. 2021), and at least 28 taxa (Winkler et al. 2020) of morphologically uniform, strict understorey, leaf litter specialists (Vaurie 1980). All are secretive and highly sensitive to habitat disturbance, and possess similar general behaviour and ecology (Vaurie 1980). Geographical ranges of Sclerurus species are dissected by the major biogeographical barriers in the Neotropics and encompass most forested environments from central Mexico to southern Brazil (d'Horta et al. 2012).

Ceará Leaftosser Sclerurus cearensis, until recently considered conspecific with Rufous-breasted Leaftosser S. scansor, differs in its slightly smaller size, slightly brighter back and underparts, clear white vs. dusky-scaled throat, and song (del Hoyo & Collar 2016). Genetic data support cearensis as an independent evolutionary lineage (d'Horta et al. 2011), although some authors (Billerman et al. 2020, Gill et al. 2021, Remsen et al. 2021) continue to treat it as a subspecies of S. scansor. S. cearensis is endemic to north-east Brazil, from southern Ceará to northern Bahia (del Hoyo & Collar 2016), and restricted to humid and dry forest habitats, with severely fragmented populations in ongoing decline due to deforestation caused by logging and agricultural expansion (Girão e Silva et al. 2018). It appeared (as a subspecies) in the Brazilian Red List for the first time in 2003 (MMA 2003), and is currently listed as Vulnerable (ICMBio 2018). Following recognition as a species, it was also categorised as Vulnerable on the IUCN Red List in 2016, where it remains until the present (BirdLife International 2021).

Breeding data for five of the seven Sclerurus species are available and are very similar (Vaurie 1980), but large knowledge gaps exist for both Short-billed Leaftosser S. rufigularis and S. cearensis (del Hoyo et al. 2020, Remsen 2020). Generally, Sclerurus nests in excavated cavities in banks or steep slopes (Sick 1997, Hilty 2002), occasionally in the soil around upended tree roots (del Hoyo & Collar 2016). The only breeding data for Ceará Leaftosser indicate that the species excavates burrows in banks (Girão & Albano 2008). Here, we review breeding data for the genus Sclerurus and present the first description of the nest and eggs of Ceará Leaftosser.

Methods

Nest description.—This was based on three nests found at two localities in Ceará state, Brazil. One was found in the Floresta Nacional do Araripe-Apodi (FLONA Araripe), a protected area in Barbalha municipality (07°17′10″S, 39°27′49″W), southern Ceará, mainly covered by typical Cerrado formations—carrasco, cerrado and cerradão—with wet forest on slopes (Silva et al. 2018). Climate is classified as ‘hot semi-arid’ under the Köppen-Geiger system (Peel et al. 2007) and is characterised by low and highly irregular rainfall, strong insolation, high evaporation rates and mean temperatures of c.27°C. Relative humidity is usually low, and the few rains are concentrated in November–April. Nevertheless, rainfall is extremely scarce in some years, causing more severe droughts. Elevation varies between 760 and 970 m (960 m at the nest site).

The second (active) and third (inactive) nests were found at the village of Catolé (04°21′23.628″S, 39°01′21.66″W; 820 m), Mulungu municipality, in the Serra de Baturité, an Atlantic Forest remnant within the Caatinga biome in northern Ceará. This remnant covers 32,690 ha and forms part of the Serra de Baturité Environmental Protection Area. Considered one of the most important forested areas in north-eastern Brazil, the Serra de Baturité is the richest area of Ceará in terms of biodiversity. Part of the serra is humid even during the long dry season. Local climate is classified as tropical with dry winter (Peel et al. 2007). Rainfall is concentrated in November–April with a well-defined dry season across the rest of the year. Mean temperatures vary between 19 and 22°C and mean annual rainfall is 1,500 mm.

At each location we made c.10 hours of observation with binoculars. Nests were measured using tape (accurate to 1 mm). Eggs were measured with analogue callipers (0.05 mm accuracy) and weighed using a digital scale (0.1 g accuracy). Nest type was determined by reference to Simon & Pacheco (2005).

Sclerurus breeding biology review.—We reviewed the primary and some secondary literature concerning the breeding ecology of Sclerurus (Goeldi 1896, Stone 1918, Todd & Carriker 1922, Pinto 1953, Herklots 1961, Skutch 1966, Monroe 1968, Skutch 1969, Wetmore 1972, Vaurie 1980, Rowley 1984, Skutch 1985, Hilty & Brown 1986, Stiles & Skutch 1989, Tostain et al. 1992, Haverschmidt & Mees 1994, Walters 1995, Kiff 1996, Zyskowski & Prum 1999, Denton & Blue-Smith 2000, Hilty 2002, Greeney et al. 2004). To update previous information, we provide a compilation of published data for each of the seven recognised species (following del Hoyo & Collar 2016).

Results

Nest, eggs and parental care of Ceará Leaftosser.—Three nests were found. The first active nest was found on 21 December 2019 (Fig. 1) in FLONA Araripe, when an adult was seen departing a bank in wet forest. It held two pure white eggs, which measured 25.7 × 19.8 mm and 24.3 × 19.6 mm, mass 5.1 g and 4.5 g, respectively.

The second nest was found on 1 June 2020, again in a bank, in the backyard of a residence in Catolé village. The nest was near a door in the house, where there was constant movement of people, and at the top of the bank, c.0.5 m from the nest, there was a frequently used trail (Fig. 2). Around the nest were several ornamental plants.

Figure 1.

Nest entrance (A), location (B) and egg (C) of Ceará Leaftosser Sclerurus cearensis, FLONA Araripe, Barbalha, Ceará, Brazil, December 2019 (Cicero Santos)

Figure 2.

Nest entrance (A) and partial view of the nest site (B–C) of Ceará Leaftosser Sclerurus cearensis, Catolé, Ceará, Brazil, June 2020 (Cecília Licarião)

Figure 3.

Schematic drawing of a Ceará Leaftosser Sclerurus cearensis nest. Mean measurements of the three nests are presented in cm ± standard deviation.

At the third nest, found by the owner of the same house, a fledgling had departed just a few days before CL arrived (1 June) at the site. This nest was in a ravine beside a dirt road in daily use by vehicles. Above the bank there was dense vegetation with 5–10 m-tall trees.

As exemplified by Fig. 3, the nest of Ceará Leaftosser can be classified as cavity/with-tunnel/low cup (sensu Simon & Pacheco 2005). Tunnels are oval in cross-section (longest on the horizontal axis) and end in a globular, expanded chamber. The cup is constructed of sticks. All three nests were excavated in earth banks 1.48 ± 0.22 m above ground. Tunnel entrances were clean and not concealed, e.g., by vegetation. Nests had the following measurements: entrance width 10.93 ± 2.0 cm (n = 3), entrance height 7.58 ± 0.51 cm (n = 3), total tunnel length (from entrance to back wall of chamber) 50.83 ± 4.25 cm (n = 3), and the centre of the nest platform was 36.5 ± 3.53 cm (n = 2) from the tunnel entrance.

Parental care.—While we measured the first nest, the adults remained in the vicinity and one approached three times trying to enter. Adults were vigilant but permitted close approach (c.5 m). When one adult was in the nest, the other always remained nearby outside, and gave an alarm call at the slightest indication of threat.

On 12 June 2020, a fledgling at the second nest made its first flight. At 07.36 h, one of the young left the nest followed by an adult. The fledgling's first flight was at a height of 1.60 m above ground. It landed 3 m from the nest, then flew again, a further 2 m. The adult gave an alarm call, flew to the nest bank, and the young flew >1 m above ground in a straight line. A few minutes later, a persistent vocalisation was heard for >10 minutes, then an adult was seen flying to the nest and perching at the entrance. When it noticed the observer (CL), it flew to a branch 2 m from the nest, uttered a series of calls and performed an agitated display. The very loud vocalisation of another young bird was heard close by, from the ground or a nearby branch. It called for c.1 minute, then flew away. The nest's contents were checked at 09.37 h using an endoscopic camera. Only recent faeces were present.

Our observations show that the breeding season occupies at least December to June. A summary of the available breeding data for each Sclerurus species based on the literature is shown in Table 1. More detailed information is as follows.

MIDDLE AMERICAN LEAFTOSSER Sclerurus mexicanus

Season December–April in Costa Rica (Stiles & Skutch 1989), possibly until at least May elsewhere. A female collected in southern Mexico in April with a fully formed egg in the oviduct (Rowley 1984), and a few specimens in breeding condition in April–May in northern Colombia (Hilty & Brown 1986). In August in eastern Ecuador, an adult was seen carrying leaves to a hole excavated 1 m up in the soil surrounding the roots of a fallen tree (Greeney et al. 2004). In the extreme south-east of the same country, G. M. Kirwan (in litt. 2021) found an active nest in a hole in an earth bank beside a little-used trail in late December. Nest a loose cup of compound-leaf rachises and dry twigs, 10 cm in diameter (Stiles & Skutch 1989) at end of a burrow (c.50 cm long) in the ground or among the roots of a fallen tree (Tostain et al. 1992). Greeney et al. (2004) recorded a 4 cm tunnel opening into a cavity roughly 20 cm in diameter. Eggs first described by Rowley (1984). Clutch two, unmarked white eggs (Stiles & Skutch 1989, Tostain et al. 1992, Kiff 1996).

TABLE 1

Summary of available breeding information for the species of Sclerurus.

Discussion

Breeding data for Sclerurus spp. show a remarkable uniformity in all aspects and are congruent with those presented here for Ceará Leaftosser. All species with available data excavate their burrows in earth masses (in the ground, in river and road banks, or in the root masses of fallen trees), and build a simple cup, usually of leaf rachises, within an expanded chamber (Zyskowski & Prum 1999). Like congenerics, probably both sexes of Ceará Leaftosser engage in all aspects of breeding. At one nest of S. cearensis, we observed two adults sharing incubation and nestling care. Although the birds were not marked and sexed, Ceará Leaftosser probably is monogamous, like S. guatemalensis (Skutch 1969, Ruth & Schreck 2020).

The apparent breeding season of Ceará Leaftosser (December–June) coincides with that of Middle American Leaftosser (December–April) in Costa Rica (Stiles & Skutch 1989). Scaly-throated Leaftosser (Skutch 1969) and Grey-throated Leaftosser (Herklots 1961) nest during October–May in Costa Rica and on Trinidad, respectively, although the latter has been found with eggs as late as June in Colombia (Todd & Carriker 1922). Species with fragmentary information also nest within this period, e.g., a Black-tailed Leaftosser with eggs in April in northern Brazil (Pinto 1953) or nestlings in June in Peru (Remsen 2020). Rufous-breasted Leaftosser starts breeding earlier, with eggs in August (del Hoyo et al. 2020).

There is a great uniformity in nests of the genus, as its more or less rudimentary structure does not seem to vary much between species (Vaurie 1980). Some, such as Middle American, Scaly-throated and Rufous-breasted Leaftossers, can use large masses of soil trapped in the roots of fallen trees to build their nests (Skutch 1969, Tostain et al. 1992, Greeney et al. 2004, del Hoyo et al. 2020). Such sites perhaps offer an alternative in level-ground sites, where banks with exposed soil can be a scarce resource.

Burrow length varies slightly among species, but is nearly always between 0.3 and 1.0 m, with the exception a 4 cm-tunnel reported by Greeney et al. (2004). Tunnels are usually straight but can be curved in Scaly-throated (Skutch 1969) and Rufous-breasted Leaftossers (Goeldi 1896), obscuring the contents from view at the entrance. Eggs of the slightly larger sister species, Rufous-breasted Leaftosser are 8% greater in size than those of Ceará Leaftosser reported here.

Nests placed in self-excavated or adopted cavities, such as a subterranean burrow, are a feature of several other furnariid genera (Zyskowski & Prum 1999). For example, all species of Geositta, which is sister to Sclerurus (Irestedt et al. 2006, d'Horta et al. 2012), breed in cavities excavated by the birds themselves or other animals (birds or mammals) (Fraga & Narosky 1985, Silva 2015, Machado et al. 2017).

For those Sclerurus with available data, the clutch is always two eggs, with just one unconfirmed report of a Rufous-breasted Leaftosser nest holding three eggs (del Hoyo et al. 2020). Eggs are always white and unmarked, but can become soiled with mud and thus appear spotted as incubation proceeds (Skutch 1969, Kiff 1996).

There are still large gaps in our knowledge of Sclerurus breeding biology, e.g., for most species, information on the length of the incubation and nestling periods, breeding success and predators are still unknown (Table 1). Short-billed Leaftosser is the least known species, with virtually no information on its reproductive habits.

Further studies of the biology of S. cearensis are essential to more fully understand its seasonality, nest site preferences and clutch size. Deforestation is the main threat to the species and, consequently, its reproductive success, but other factors that can negatively impact the latter are unknown, and deserve study.