Northern Harrier Breeding in Bahía de San Quintín, Baja California: A UniqueDiscovery of Nesting in Salt Marshes
The Northern Harrier (Circus hudsonius), a raptor known for its distinctive dimorphism and widespread presence across North America, has made an unexpected impression in the wetlands of Bahía de San Quintín, Baja California. Known for wintering as far south as Central America and sometimes even reaching Colombia and Venezuela, this species typically breeds in more northern regions. However, in recent years, scientists have uncovered successful nesting in one of the southernmost parts of its breeding range—San Quintín Bay.
A Southern Range Extension
The discovery of Northern Harriers breeding in the salt marshes of Bahía de San Quintín is a significant one. The region, which is home to diverse tidal salt marshes, appears to be at the southern limit of the species’ breeding territory. Observations from 2023 suggest that as many as 15 pairs of Northern Harriers may be nesting in this area. This finding is especially remarkable given the rarity of such records in Baja California, where nesting observations have historically been scarce.
In April 2023, a team of researchers led by biologists from Universidad Autónoma de Baja California and CICESE began monitoring bird activity in the region. They observed three pairs of Northern Harriers flying over a 0.5-hectare section of wetland. The behaviors exhibited by the birds, including aggressive territorial defense and nuptial flights, suggested that at least one pair might be nesting. Their suspicions were confirmed when they discovered a nest a few weeks later, with two eggs and one chick present.
Nesting in Salt Marshes: A Rare Phenomenon
The nest, located in the Cielito Lindo area of the bay, was situated in a dense patch of Salicornia and Spartina, a type of wetland vegetation. While Northern Harriers typically prefer nesting in more open, grassy wetlands, their choice of the dense salt marsh habitat is a notable deviation from the norm. The nest itself was constructed without any human-made materials, made from natural sea grasses and vegetation, and was well-covered by the surrounding plants. The researchers returned to monitor the nest and, by April 26, had documented the hatching of a second chick.
By June 17, the fledglings had successfully left the nest, with the male harrier observed feeding the young birds. This successful breeding event in such a specific habitat is a testament to the resilience of the Northern Harrier and its ability to adapt to unique environments.
A Species of Special Concern
Despite being classified as a species of least concern by the International Union for Conservation of Nature (IUCN), the Northern Harrier is considered a species of special concern in California and a conservation priority in the United States. Its primary threat comes from the ongoing loss of wetland habitats—areas critical to the bird's breeding success. The wetlands of Bahía de San Quintín, however, appear to be a safe haven for these harriers, providing a habitat that supports their unique nesting habits.
The findings in Bahía de San Quintín represent not only the southernmost known breeding site for the Northern Harrier but also a crucial piece of the puzzle in understanding the species’ distribution and breeding behavior. Given the relatively small size of the population in this area, the successful nesting of up to 15 pairs in the region is an important indicator of the health of local wetland ecosystems.
Ongoing Research and Conservation
These observations are part of ongoing research efforts funded by the California Department of Fish and Wildlife, which aims to protect and conserve coastal wetlands and their associated wildlife. The discovery of a thriving population of Northern Harriers in Bahía de San Quintín highlights the importance of preserving these critical ecosystems. As wetland habitats face growing threats from development, pollution, and climate change, it is more important than ever to monitor species like the Northern Harrier and ensure their protection.
The successful nesting of Northern Harriers in Bahía de San Quintín is a reminder of the resilience of wildlife in the face of environmental change and underscores the significance of continued conservation efforts in preserving vital wetland habitats for future generations.
The coauthors and institutions involved in the writing of the scientific note are:
Xavier Moreno and Gonzalo de León-Girón- Colección de Vertebrados, Facultad de Ciencias, Universidad Autónoma de Baja California, Ensenada, Baja California, México.
Hiram Rafael Moreno-Higareda- CICESE, Ensenada, Baja California, México; Universidad Autónoma de Baja California, Ensenada, Baja California, México.
Lori Hargrove- San Diego Natural History Museum, San Diego, California, USA.
Enrique D. Zamora-Hernández- B. Botaris, Punta Banda III, Ensenada, Baja California, México.
Daniel Olguín- Terra Peninsular, Ensenada, Baja California, México.
Horacio de la Cueva- CICESE, Ensenada, Baja California, México; Terra Peninsular, Ensenada, Baja California, México.
