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Reproductive Success and Diet of the Swainson’s Hawk (Buteo swainsoni) in the Grasslands of Janos, Chihuahua, Mexico
by
, , , and
Nereyda N. Cruz Maldonado
1
,
Cayetano J. Villareal Lozoya
2,
Javier Cruz Nieto
3,
Alina Olalla Kerstupp
4,
Gabriel Ruiz Aymá
4,
Antonio Guzmán Velasco
4 and
José I. González Rojas
5,* 1
Comisión Nacional Forestal (CONAFOR), Pasaje Siglo XXI N° 203, Fracc. El Sauz, Saltillo 25294, Coahuila, Mexico
2
World Wildlife Fund (WWF), Ave. Insurgentes Sur 1216, Tlacoquemecatl del Valle, Benito Juárez, Ciudad de México 03100, Mexico
3
Organización Vida Silvestre, A.C. (OVIS), Keramos Pte 225, Col. Del Prado, Monterrey 64410, Nuevo León, Mexico
4
Laboratorio de Biología de la Conservación y Desarrollo Sustentable, Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León (UANL), Cd. Universitaria, San Nicolás de los Garza 66455, Nuevo León, México
5
Laboratorio de Ornitología, Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León (UANL), Cd. Universitaria, San Nicolás de los Garza 66455, Nuevo León, México
*
Author to whom correspondence should be addressed.
Animals 2026, 16(1), 131; https://doi.org/10.3390/ani16010131
Submission received: 28 November 2025
/
Revised: 27 December 2025
/
Accepted: 30 December 2025
/
Published: 2 January 2026
(This article belongs to the Section Birds)
Simple Summary
The Swainson’s Hawk is a migratory raptor that breeds in the grasslands of northern Mexico, but little is known about its ecology in this region. We studied its reproduction, nest locations, and diet in the Janos grasslands of Chihuahua. We monitored 18 nests and found that less than half produced fledglings, mainly because young hawks (nestlings) had much lower survival than eggs during incubation. Nests were usually placed in mesquite trees located away from towns and in areas with low human disturbance. By analyzing pellets and prey remains, we found that the hawks fed mostly on vertebrates, such as small mammals and lizards. These findings highlight the importance of conserving natural grasslands and monitoring populations over time to support this species’ long-term survival.
Abstract
Understanding the breeding ecology and trophic dynamics of the Swainson’s Hawk (Buteo swainsoni) is essential for conserving grassland raptor populations in northern Mexico. We evaluated reproductive success, nest-site characteristics, and diet of the species in the grasslands of Janos, Chihuahua, during the 2006 breeding season. Eighteen nests were monitored to estimate daily survival rates (DSRs) using the Mayfield method. Overall nest success was 44.4%. DSR declined significantly from incubation (0.99 ± 0.00079) to the nestling stage (0.98 ± 0.00087; z = 8.5, p < 0.001), resulting in cumulative survival of 79.9% and 56.2%, respectively. Successful nests tended to occur farther from towns, although this trend was not statistically significant. Most nests were built in mesquite trees at intermediate elevations and in areas with low human disturbance. Diet analyses of 56 pellets and 91 prey remains revealed a predominance of vertebrates (63.17%), mainly mammals and reptiles, with vertebrate frequency significantly exceeding that of invertebrates (χ2 = 23.19, p < 0.001). These results highlight the species’ reliance on vertebrate prey and the vulnerability of the nestling stage, underscoring the importance of long-term monitoring in semi-arid grasslands.
Keywords:
Swainson’s Hawk; nesting ecology; reproductive success; diet; predation; grasslands; México
