Nest predation of the Chestnut Seedeater Sporophila cinnamomea (Passeriformes: Thraupidae) by the Patagonian Green Racer Pseudablabes patagoniensis (Serpentes: Dipsadidae) in the Brazilian Pampas

ROSONI, J. R. R.; FONTANA, C. S.; CARLOS, C. J.

Herpetology notes

Societas Europaea Herpetologica

Año: 2023 vol. 48 p. 217 - 218

2071-5773

Nest predation is the most important factor causing breeding failures in birds (Repenning and Fontana, 2016; Franz and Fontana, 2021) and can influence the ecology and evolution of life history traits (DeGregorio et al., 2014). Predation events of birds nests by other vertebrates are common, yet they still need to be well documented (Smith and Atkinson, 2017). Snakes are significant nest predators in warm areas and may be responsible for up to 35% of predation events (DeGregorio et al., 2014). Eggs and nestlings of altricial species form a substantial part of snakes´ diet during birds´ breeding period. In addition, eggs and nestlings are attractive prey because they are sessile, allowing snakes to use their timing for consumption once they locate nests (Stake et al., 2005). Here, we describe a predation event of a Patagonian Green Racer Pseudablabes patagoniensis (Girard, 1858) (Serpentes: Dipsadidae) on nestlings of the Chestnut Seedeater Sporophila cinnamomea (Lafresnaye, 1839) (Passeriformes: Thraupidae) in the Pampas biome of southern Brazil.The Patagonian Green Racer is a diurnal and predominantly terrestrial snake that inhabits open vegetation formations, such as savannahs, grasslands, wetlands, and floodplains in Argentina, Brazil, Paraguay, Bolivia, and Uruguay (Giraudo and Scrocchi, 2002; Quintela and Loebmann, 2019). It is a generalist species, feeding mainly on anurans, lizards, snakes, small mammals, birds, and occasionally insects and fish (López and Giraudo, 2008; Zocche et al., 2017; Quintela and Loebmann, 2019).The Chestnut Seedeater is a small-sized passerine about 10 cm long and 9 g in weight. It breeds in grasslands and wetlands of northeastern Argentina, west and extreme southeast of Uruguay, extreme south of Paraguay, and southern Brazil, during austral spring and summer (Ridgely and Tudor, 1989). After breeding, it migrates north to the grasslands of the Cerrado of Central Brazil (Rosoni, 2022). The species is globally Vulnerable owing to a rapid population reduction caused by habitat fragmentation and loss and trapping for the bird trade (BirdLife International, 2023). The species exhibits sexual dichromatism, with males mostly chestnut with a grey cap, wings, and tail (Fig. 1A) and females uniform dull brownish (Repenning and Fontana, 2019; Jaramillo, 2020). Chestnut Seedeaters build their low-cup nests of grass stems, inflorescences, and rootlets on shrubs, clumps, and herbaceous plants 42–51 cm above wet or dry ground or water. The clutch size varies from one to three but is usually two (Rosoni et al., 2020).We recorded the predation event on 4 December 2020, at 16:48 h, in a wetland area in Quaraí (-30.4860°S, -56.3311°W), western Rio Grande do Sul. The average temperature in the region at the time of the observation was 27 °C (range 14.5–28 °C), and the relative humidity was 31% (range 30–94%), according to the nearest meteorological station (INMET, 2023).The two-day-old nestlings, with closed eyes and some light gray down feathers on the upper parts (Fig. 1B), were in a nest 42 cm high in a clump of the grass Andropogon virgatus (Poaceae). When we approached the nest, we noticed a snake about 60 cm long seizing the first nestling (Figs. 1C and 1D). Then, the snake left the nest towards the clump´s base, where it ingested the first nestling. We decided to install a camera to record if the snake would return to prey on the second nestling. After removing the first nestling, the snake returned from the base of the clump of vegetation to the nest after 12 minutes, forcing a hole through the nest´s wall and capturing the second nestling, which was swallowed in just 1 min and 12 sec (see video here: https://www.youtube.com/watch?v=QJJxpPurP6Q). During two hours of continuous recording after predation, the female Chestnut Seedeater visited the nest eight times. Visits lasted, on average, 1 min and 31 sec (range 10 sec – 4 min and 34 sec). In all visits, the female ingested the food she was carrying in her bill after not finding the nestlings. On six occasions, the female looked for the nestlings inside, outside, and below the nest. On two occasions, the female displayed a brooding behaviour (i.e. sitting on nestlings to keep them warm) as if the nestlings were in the nest; simultaneously, she repaired the hole in the nest´s wall; on the last visit, the female did not approach the nest, vocalising from a distance.Our record provided relevant behavioural information for the Patagonian Green Racer, such as the duration of the visit, attack latency to the prey, and the return to the nest after the first predation event, which are rarely reported in detail (Stake et al., 2005). Patagonian Green Racer has an olive-green colour with black spots that helps its camouflage among grassland vegetation (Hartmann and Marques, 2005; Gouveia et al., 2017). Such a colouration pattern is advantageous for a snake that hunts and evades visually-oriented predators during the day (Hartmann and Marques, 2005). Furthermore, during snakes´ foraging activity nest height is a factor that can influence the frequency of nest encounters (Ferreira et al., 2022). Additionally, according to Skutch (1949), snakes find nests in the Neotropical region following adult birds´ movement while amid vegetation.Several studies reported predation of Sporophila Seedeater´s nests by snakes. For example, in southern Brazil, nests of the Tropeiro Seedeater S. beltoni Repenning & Fontana, 2013 and the Tawny-bellied Seedeater S. hypoxantha Cabanis, 1851 were preyed upon by Lichtenstein´s Green Racer P. olfersii (Lichtenstein, 1823) and Brazilian Green Racer P. aestiva (Duméril et al., 1854), respectively (Repenning and Fontana, 2016; Franz and Fontana, 2021). Likewise, in the Brazilian Cerrado, a juvenile Yellow-bellied Seedeater S. nigricollis (Vieillot, 1823) was predated in the nest by a Lichtenstein´s Green Racer (Ferreira et al., 2022). Here we reported the first record of predation of the Chestnut Seedeater by the Patagonian Green Racer. Therefore, our record contributes to knowledge of the snake´s diet in southern Brazil, thus supporting the importance of birds as part of the diet of this species.