Observation: In the identification expedition in the islands Santa Margarita and Magdalena, I observed a pair of bald eagles (Haliaeetus leucocephalus) perched on the local vegetacion (xerophilous shrub, cardon cactus; Figures 1 and 2) and on the fly (Figures 3 and 4), this while we were hiking and every time we circled the islands on boat.
Marine birds expert: In the Baja California peninsula we can find part of the breeding population of the bald eagle (Haliaeetus leucocephalus), which is distributed from Alaska (U.S.) to northern Mexico [1], with Santa Margarita and Magdalena islands within its nesting range. However, if we the review historical records of this species, we find that its population was reduced along the peninsula, being restricted to Bahía Magdalena [2], mainly as a result of chemical pollution by pesticides such as DDT, known for decreasing its reproductive success [1, 4]. In fact, for a long time only one to three pairs of adults were observed per year in the bay [2,3], which was very alarming since the Magdalena Bay islands were considered the strength of the population [2]. These eagles build their nests on large rocks in the islands (such as Santa Margarita Island) and in the top part of the mangrove (up to 4 m tall), although the placement of a nest on cardon (Pachycereus pringlei) is also probable [1].
It's important to mention that this eagle species is currently cataloged as endangered in Mexico [5], so records of sightings like these are of great importance. In addition, because it is an apex predator it is considered a indicator species of the health of the ecosystem [1]. Fortunately, at present a greater number of breeding pairs are estimated per year in Baja California Sur (between 5 and 8 pairs). But this is still a low number, which is why the bald eagle needs to be protected from possible threats (the presence of invasive species, loss of habitat, pollution, illegal capture, among others) to be able to conserve their small and isolated populations [1].
For more information about the biology of this species, visit this site.
Consultant:
María Félix-Lizárraga. Aves Marinas (Coordinación). Grupo de Ecología y Conservación de Islas A.C.
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References:
Rodríguez, R. y Rivera, L. 2009. Ficha técnica de Haliaeetus leucocephalus. En: Escalante-Piego. P. (compilador). Fichas sobre las especies de aves incluidas en Proyecto de Norma Oficial Mexicana PROY-NOM-059-ECOL-2000. Parte 1. Instituto de Biología, UNAM. Bases de datos SNIB-CONABIO. Proyecto No. W007. México, D.F.
Henny, C.; Conant, B. y Anderson D. 1993. Recent distribution and Status of Nesting Bald Eagles in Baja California, Mexico. J. Raptor Res. 27(4):203-209.
Hastings R. y Fischer D. 2001. Management priorities for Magdalena Bay, Baja California, Mexico. Journal of Coastal Conservation 7: 193-202.
Sharpe, P. y Garcelon, D. 2005. Restoring and monitoring Bald Eagles in Southern California: the legacy of DDT. Páginas 323-330 en Garcelon, D. K. y C. A. Schwemm (eds). Proceedings of the Sixth California Islands Symposium, Ventura, California.
Norma Oficial Mexicana NOM-059-SEMARNAT-2010. Protección ambiental. Especies nativas de México de flora y fauna silvestres. Categorías de riesgo y especificaciones para su inclusión, exclusión o cambio. Lista de especies en riesgo.
Figura 1. Ejemplar adulto de águila calva (Haliaeetus leucocephalus), observado durante la expedición de reconocimiento, 2015.
Figura 2. Ejemplar de águila calva (Haliaeetus leucocephalus) perchado sobre la vegetación insular, 2015.
Figura 3. Ejemplar de águila calva (Haliaeetus leucocephalus) sobrevolando la isla, 2015.
Figura 4. Ejemplar de águila calva (Haliaeetus leucocephalus) iniciando el aterrizaje, 2015.
