Introduction

The Bicolored Hawk Accipiter bicolor (Vieillot, 1817) is a neotropical resident raptor present in humid and deciduous forests, in lowlands and subtropics, from sea level to 2000 meters of altitude, and his geographical distribution encompasses from central Mexico to southern Chile and Argentina (^{Bierregaard et al. 2020}). The habitat preference of A. bicolor is both moist and deciduous forests, even though is rare observe it (^{Ridgely & Greenfield 2019}); it has been observed since the forest understory, approximately 5 m, till to the canopy, above 15 m (^{Parker & Carr 1992}). Accipiter bicolor hunt by active aerial pursuit or ambush (Bierregaard et al. 2020; ^{Thorstrom 2012}), and has been considered a stealthy and discreet hunter, but also bold or daring (Ridgely & Greenfield 2019).

The diet of A. bicolor mainly includes birds (^{Barrio et al. 2015}, ^{Edgardo-Arévalo & Fernández-Otárola 2014}, ^{Mader, 1981}; ^{Stiles et al. 1989}; ^{Thorstrom & Quixchán 2000}); also lizards and small mammals, although the identification of these prey is uncertain. In the literature, the mammal prey of A. bicolor includes one species of squirrel (Sciurus sp.), 3 species of rodents, and 4 species of bats, but the reports don’t provide a taxonomic identification at the species level (^{Robinson 1994}, Thorstrom 2012). Another example can be checked in a report about the hunting behavior of A. bicolor on bats in the surroundings of the 'Volcán de los Murciélagos' cave in Mexico, but don’t provide an identification of these prey either (^{Mikula et al. 2016}). Accipiter bicolor is widely distributed in the Neotropics but knowledge about its ecology is scarce (^{Ridgely & Greenfield 2019}).

Recently, various platforms of citizen science approach such as iNaturalist and eBird report observations of wildlife in urban areas, these reports constitute an exceptional opportunity to filling a gap in knowledge on several ecological aspect as the diet, life history, behavior. In this work, we document the presence of Accipiter bicolor in urban areas of Guayaquil city and forest remnants near, also provide new records about his diet, and discuss possible foraging strategies in synanthropic environments.

Material and methods

Study area. Guayaquil is the capital city of Guayas province, in Ecuador, and is located at the beginning of the Guayas River. It presents different streams belonging to the inner estuary of the Gulf of Guayaquil, and has a tropical climate, with an average annual rainfall that ranges between 750 and 1000 mm, with an average annual temperature between 24.5 and 26 °C (GAD Municipal Guayaquil 2014). The elevations vary between 50 to 400 meters above sea level and have native forest remnants that correspond to mangroves and tropical dry forests, also known as lowland deciduous forest of the equatorial Pacific (Ministerio del Ambiente del Ecuador 2013).

Field observations. Two birdwatching counts were developing: a survey in January 2018, and a casual observation in February 2021. In the first field observation, DAC and Jorge Luis Vélez Del Hierro carried out a bird count from 6:00 to 9:00 am in an urban area near to streams and mangroves, using Eagle Optics Ranger 8x42 binoculars, and with a Canon PowerShot SX40 HS camera. The hawk was identified as A. bicolor for present gray plumage and the rufous color on his thighs, as well as for the tail length and presence of bars on it (^{Bierregaard et al. 2020}, ^{McMullan & Navarrete 2017}). The prey was identified following bird field guides (McMullan & Navarrete 2017, ^{Ridgely & Greenfield 2006}).

The second observation was opportunistic, where MA, DAC, CB, and RM noticed, observed, and photographed an immature individual of Accipiter bicolor while eat a bat in a street in an urban area. The hawk was identified by the diffuse brown hue of its plumage, as well as by the characteristics described above (^{Bierregaard et al. 2020}, ^{McMullan & Navarrete 2017}); the bat was identified by external morphological characteristics from photographs (^{Tirira 2017}, ^{Salas et al. 2018}). For validate taxonomic identification of bat and complement information about the possible hunting strategy of the hawk, JAS searched for bat refuges in this urban sector.

Records from citizen science. Finally, we search observations of Accipiter bicolor in the city of Guayaquil and its surroundings up to about 15 km, that includes forest remnants and natural reserves, from the Global Biodiversity Information Facility (GBIF 2022), and was validate with a review of records from citizen science biodiversity information platforms (eBird 2021, iNaturalist 2022). With these records, we generate a map of occurrences of the species in the software QGIS 3.16 Hannover (QGIS 2022). All records used were research-grade data quality assessment which means that every observation has a specific date of the event, location, photos, ID supported by two or more birdwatchers.

Results

Prey species registered. The first observation was made on January 13, 2018, at the Malecón Universitario del Estero Salado in Guayaquil (2°8’S, 79°55’W), and an adult individual of Accipiter bicolor was observed while ate an Ecuadorian Ground Dove Columbina bluckeyi (Sclater & Salvin 1877) (Columbiformes: Columbidae), on a tree of saman (Samanea saman: Fabaceae). This prey was plucked and dismembered, on the branch of a saman tree, for later consumption. Supplementary material for this observation can be found at the following link (https://ebird.org/checklist/S41866794).

In the second observation, another individual of A. bicolor was observed on the ground, while ate a bat, with pedestrians and vehicular traffic in the urban center of the city of Guayaquil (2°11.098'S, 79°52.699'W), at the Loja street, near to Escuela Superior Politécnica del Litoral, Campus Las Peñas. This hawk shows an elusive behavior: he moved the prey a few meters ahead, doing small jumps, staying alert, while the pedestrians observed it; this behavior lasted thirty minutes (Fig. 1a). Additional photographic and video materials are available on the eBird portal (https://ebird.org/checklist/S80558783), and the link: https://zenodo.org/record/7530296#.Y8BRI3ZBzZY. The prey was identified as Fraternal Fruit-eating Bat Artibeus fraterculus Anthony, 1924 (Phyllostomidae: Stenodermatinae), based on the external characteristics observed such as brownish coloration and intensity of the facial lines, which make distinguish from congeners such as A. lituratus or A. aequatorialis.

Later, on July 12, 2021, between 8:00 and 10:00 am, JAS found a colony of Artibeus fraterculus roosting in a disuse old jail (2°11'0.75"S; 79°52'45.74"W; Figure 1b), located approximately 160 meters from the site of the second observation. This structure dates from 1907 and is currently listed as a heritage site (M. I. Municipalidad de Guayaquil 2014). The old prison has a yard with three trees of Ficus obtusifolia (Moraceae) (Fig. 1c); inside, on the ground floor, there were 6 cells within small groups of 3 to 11 individuals of A. fraterculus, with a total of approximately 50 individuals (Fig. 1 d, e).

Accipiter bicolor records in Guayaquil. Finally, we obtained 59 records of Accipiter bicolor from Guayaquil and surrounding areas (Table 1), between the years 2007 and 2022, which include 5 reserves: Isla Santay Recreation National Area, La Prosperina Protected Forest, Manglares El Salado Fauna Production Reserve, Cerro Blanco Protected Forest, and Parque Lago Recreation National Area. The resulting map shows two peri-urban reserves with the most observationrecords: Cerro Blanco (n=26), La Prosperina (n=10), and three reserves with scarce records as Isla Santay (n=7), Parque Lago (1), El Salado (1); in addition, there were 14 records of this species inside urban areas, in highly altered habitats (Fig. 2).

Figure 1 A) Immature individual of Bicolor Hawk (Accipiter bicolor) eating a Fraternal fruit-eating bat (Artibeus fraterculus) in the center zone of Guayaquil, Ecuador; B) y C) Doorway and inner yard of the old jail; D) y E) Individuals of A. fraterculus inside the cells. Photos by MA (A) and JAS (B, C, D, E). 

Figure 2 Map of records of Bicolored Hawk Accipiter bicolor in Guayaquil and surrounding areas from 2007 to 2022. The records were taken, filtered, and validated from Ebird, iNaturalist, and GBIF. Arabic numbers indicate the reserve's names: 1) Cerro Blanco Protected Forest, 2) La Prosperina Protected Forest, 3) Isla Santay Recreation National Area, 4) Manglares El Salado Fauna Production Reserve, 5) Parque Lago Recreation National Area. Capital letters indicate the localities described in the field phase. A) Malecón Universitario del Estero Salado, B) Loja street, in the center zone of Guayaquil. 

Discussion

Herein we report two new prey for Accipiter bicolor from Western Ecuador, being remarkable because they came from a densely populated and highly altered coastal urban area, which had not been previously reported (^{Bierregaard et al. 2020}, ^{Ridgely & Greenfield 2019}); the presence of A. bicolor in urban environments may be due to the availability of shelter and food (^{Bernat-Ponce et al. 2022}). The record of Columbina buckleyi as part of A. bicolor's diet is consistent with other prey reported before as doves or similar size birds (^{Stiles et al. 1989}); the Columbina doves are abundant and easily observable in the urban area and parks of Guayaquil (^{Rojas-Allieri & Man-Ging 2014}). Nevertheless, the capture of a bat during the day in urban areas raises some questions, due to the capture strategy used and the availability of food resources.

Accipiter bicolor is a stalker-type opportunistic predator (^{Bierregaard et al. 2020}), it is probable that the juvenile of A. bicolor extracted the bat from the old jail, using the trees to perch, and then entered the cells to hunt since it can maneuver in small spaces (Bierregaard et al. 2020). Urban bats can be an easily accessible food resource for predators, such as falcons or accipritids, which have been reported near these urban roosts (^{Mikula et al. 2016}). The presence of Artibeus fraterculus has been reported in Guayaquil previously (^{Salas et al. 2018}), and it is a species that adapts easily to using human structures as shelters (^{Pinto et al. 2013}), so it is a food resource easily accessible by predators. Previously, only the barn owl Tyto alba had been reported as a predator of A. fraterculus (^{Moreno 2010}, ^{Thomas & Thomas 1977}); other authors had suggested that owls such as Pulsatrix perspicillata, Glaucidium peruvianum, Megascops roburatus, Strix nigrolineata, S. virgata, or the bat-hunter falcon Falco rufigularis may be potential predators, based on observations of predation on other species of Artibeus (Salas et al. 2018).

Accipiter bicolor has been recorded in various localities around Guayaquil, mostly in forested areas, but there were no records in highly disrupted areas before. The oldest georeferenced records of this species near Guayaquil date from 1991, in Cerro Blanco reserve (^{Berg 1994}, ^{Parker & Carr 1992}). Later, ^{Mischler (2012}) present an update of birds in this same reserve, and report it as rare, and as breeding in the wet season; currently this reserve has most of the sightings of this species. The second most locality near Guayaquil of A. bicolor was in La Prosperina Protected Forest but was not previously registered on this reserve (^{Pozo-Cajas et al. 2017}). Otherwise, the presence of Accipiter bicolor in disrupted areas would suggest that this species is adaptable to synanthropic environments, presumably for the available food and less competition with another hawk, especially for young individuals (^{Tapia & Zuberogoitia 2018}); however, it is necessary to complement the ecology knowledge of this species with studies of habitat use, as well as the degree of dependence of this species on natural habitats (^{Rullman & Marzluff 2014}).

Diet reports in raptors are very scarce in Ecuador, only a few reports are known from pellets of nocturnal raptors as owls (^{Brito et al. 2015}, ^{Freile et al. 2012}, ^{Moreno 2010}). The urban areas of the city of Guayaquil, and its surrounding natural areas provide an important logistical facility to develop these observations, so it is advisable to continue monitoring or participating in citizen science approach to complement and add more information on the ecology and diet of raptors.