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Acta zoológica mexicana

On-line version ISSN 2448-8445Print version ISSN 0065-1737

Acta Zool. Mex vol.32 n.1 Xalapa Apr. 2016

 

Notas Científicas

Caracara cheriway predation on migratory waterbirds, Egretta thula and Podiceps nigricollis, in Southern Baja California Peninsula

Depredación de Caracara cheriway sobre las aves acuáticas migratorias, Egretta thula y Podiceps nigricollis , en el Sur de la Península de Baja California

Claudia J. Pérez-Estrada1  * 

Ricardo Rodríguez-Estrella1 

1 Centro de Investigaciones Biológicas del Noroeste, S.C. (CIBNOR), Av. Instituto Politécnico Nacional 195, Colonia Playa Palo de Santa Rita, C.P.23096, La Paz, Baja California Sur, México. estrella@cibnor.mx

Resumen:

Reportamos la depredación de aves acuáticas migratorias por Caracara cheriway. El 4 de enero del 2015 se observó a un caracara juvenil alimentándose de Egretta thula (juvenil) y a un caracara adulto de Podiceps nigricolis (adulto) en una playa al sur de la península de Baja California. Este es el primer reporte de Caracara cheriway depredando presas vivas de aves acuáticas migratorias.

The crested caracara Caracara cheriway (Falconidae) is a medium-sized raptor (1050-1300 g), with a range from the southernmost United States, central and southern Florida, southern Texas, southern Arizona, Baja California Peninsula through Mexico and Central and South America (Morrison & Dwyer, 2012). The crested caracara is a very common raptor throughout the Baja California Peninsula, but far more abundant south of 28°N (Wilbur, 1987, Rodríguez-Estrella et al., unpubl. data). In spite of its wide range, little is known of its feeding habits. This caracara was previously considered a primary carrion feeder (Bailey, 1925, Bent, 1938). It is now considered a generalist and opportunistic forager, taking a wide variety of live vertebrate and invertebrate prey, as well as carrion, from a variety of habitats, but primarily open habitats (Rodríguez-Estrella & Rivera, 1997, Travaini et al., 2001, Martinelly, 2010, Morrison & Dwyer, 2012). In this note, we present two observations of the crested Caracara preying on the snowy egret and eared grebe during winter in the southern part of the Baja California Peninsula.

The snowy egret Egretta thula (Pelecaniformes, Fam. Ardeidae) and the eared grebe Podiceps nigricollis (Podicipediformes, Fam. Podicipedidae) are two migratory waterbirds entering the Baja California Peninsula. E. thula overwinters throughout Mexico and Central America southward to Panama (Ridgely & Gwynne, 1989, Stiles & Skutch, 1989, Howell & Webb, 1995). This species nests in the Baja California Peninsula at Laguna Ojo de Liebre, San Ignacio, and Isla San José (Wilbur, 1987). P. nigricollis has a winter range that is fairly restricted. Both species migrate to the Peninsula to overwinter. The vast majority of the eared grebe, hundreds of thousands of birds, overwinters on islands in the north and central Gulf of California (Cullen et al., 1999); several thousand spend the winter on salt flats at Guerrero Negro in the State of Baja California Sur (Carmona & Danemann, 1998).

Both waterbird species feed on a wide variety of aquatic prey. Eared grebe (ca. 500 g) prey mainly on invertebrates, including small crustaceans (Cullen et al., 1999) and snowy egret (370 g; Palmer, 1962) prey upon earthworms and annelid worms, aquatic and terrestrial insects and crabs, marine fish, and even frogs, snakes, and lizards (Kushlan, 1978a, 1978b, Parsons & Master, 2000). However, there is no information on predators of either species and certainly nothing on predation in their wintering grounds (Cullen et al., 1999, Parsons & Master, 2000). In this note, we present two observations of the crested Caracara preying on the snowy egret and eared grebe during winter in the southern part of the Baja California Peninsula.

On January 4, 2015 between 11:35 to12:00 H we observed an aggregation of migratory waterbirds feeding near the shore at a beach named CIBNOR El Comitán (24°08'12.3"N, 110°25'31.50"W), 15 km North of La Paz city. This beach is shallow frequently having an accumulation of algae near the coast, where abundant invertebrates and small fishes feed on and rest. Thus, migratory and resident waterbirds usually are observed feeding over there. We observed during high tide eared grebes (juveniles, adults), snowy egrets (juveniles), brant goose (Branta bernicla, adults), marbled godwit (Limosa fedoa, adults) and snowy plovers (Charadrius alexandrines, adults) foraging in the wetland. No carcass of any waterbird was observed in the area at the beginning of observations at 11:44. At 15:53 with low tide we observed that eared grebes and snowy egrets were not longer in the area, they flew away, and two individuals of crested caracara, a juvenile and an adult, were feeding on recently killed snowy egret juvenile and eared grebe adult, respectively (Fig. 1a, b). We suggest caracaras killed these waterbirds. When the caracara adult became aware of our presence (at 15:59), it took and carried the grebe with its beak (Fig. 1c); suddenly, the caracara drop the rest of the carcass and flew directly where the juvenile was feeding on the snowy egret (approximate distance, 32 meters). At 16:00 both the adult and juvenile continued feeding on the remains of the egret body (Fig. 1d). At 16:03 the juvenile flew away from the site and the adult caracara continued feeding on until 16:09, when it left the area.

Figure 1: (a) Adult feeding on P. nigricollis at 15:53 h; (b) juvenile feeding on Egretta thula; (c) adult holding the P. nigricollis body in its beak; (d) adult and juvenile caracara feeding on E. thula. Note that prey are fresh and that tide was very low at the time of prey consumption. 

The crested caracara is a carrion eater and frequently performs kleptoparasitim and hunts live prey, mostly small items (Glazener, 1964, Yosef & Yosef, 1992, Rodríguez-Estrella & Rivera, 1992, 1997). Crested caracaras may prey on live small birds, lizards, snakes, rabbits (Sylvilagus spp.) and rodents (Bent, 1938, (Whitacre et al., 1982, Rodríguez-Estrella & Rivera, 1997, Travaini et al., 2001). There are only few reports of crested caracara hunting waterbirds white ibis (Eudocimus albus; weight 750-1050 g; Bent, 1938), cattle egrets (Bubulcus ibis; weight 270-512 g; Layne et al., 1977, Whitacre et al., 1982) a prey-size bigger than its common medium prey size (Rodríguez-Estrella & Rivera, 1997) but likely within the range of birds that can be preyed upon by caracaras. None report existed about predation on waterbirds in wintering grounds and it is certainly important to determine the potential causes of death for wintering birds. Of special relevance in our report is that apparent predation was observed on two different waterbird species at the same time in the same area by one adult and one juvenil crested caracara. It has been noted that pairs of caracara adults can coordinate attacks on cattle egrets (Whitacre et al., 1982) and white ibis (Barbour, 1923). However, adults can teach juveniles to hunt preys and lead juveniles to predictable food sources (Rodríguez-Estrella & Rivera, 1997). We do not know if the successful capture of two waterbird species in our study area could be the result of coordinated hunting, but a concentration of migratory birds might increase their risk of predation. Our observations increase the knowledge of the predatory life history of crested caracara on live prey, particularly in coastal wintering grounds.

Acknowledgements

We appreciate the comments of three anonymous reviewers that improved a first draft. Ira Fogel of CIBNOR provided editorial services. Funding was provided by SEP-CONAYT (155956) and CIBNOR grants.

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Received: October 13, 2015; Accepted: February 17, 2016

Autor para correspondencia: e-mail: *claudiap@cibnor.mx

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