Ferruginous Hawks (Buteo regalis) appear to be increasing in number during their winter stay in California, despite the fact that their preferred grassland habitat has been decreasing for over two decades. Unfortunately, this decline in open areas has resulted in the expected decline of many other grassland bird species across western North America.
In their recent publication titled “Population Trends of the Ferruginous Hawk (Buteo regalis) Wintering in California” in the Journal of Raptor Research, lead author Edward Pandolfino, along with co-authors Lily Douglas from the U.S Fish and Wildlife Service and Chris Ray from The Institute for Bird Populations, put forward possible explanations for the unexpected population fluctuations observed in the Ferruginous Hawk.
Citizen science has the potential to shed light on surprising realities that take place on raptor wintering grounds. This particular phase of their annual cycle often receives less focus compared to the breeding season, but it holds significant implications for the overall health and well-being of these species.
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Studying Ferruginous Hawks can pose a challenge due to various factors. Unlike many other migratory hawks, they do not gather in predictable locations along topographical features such as ridges. This makes it difficult to reliably observe them at migration count sites. Furthermore, population data on these hawks is often contradictory, leading to variations in their conservation status across different states, regions, and even countries. For instance, in California, many of the Ferruginous Hawks that winter there breed in Washington or Oregon, where they are respectively listed as endangered and sensitive-critical species.
In order to gain a better understanding of the species’ current status, Pandolfino and his team conducted an analysis using a citizen science dataset from the wintering grounds of the Washington-Oregon cohort. The researchers focused on five Bird Conservation Areas in California that had been subject to Christmas Bird Counts (CBCs) between 1998 and 2022.
CBCs are conducted by birders and bird-related organizations on a voluntary basis. They follow a standardized protocol to gather information on bird species during the month of December. These counts offer a comprehensive dataset for determining the presence of Ferruginous Hawks in a key area of their habitat, surpassing what a typical research team would be able to collect under normal project conditions.
The team’s analysis uncovered a surprising finding – despite a significant decrease in habitat quality over the course of 25 years, the population of Ferruginous Hawks in California actually increased during winter. This finding was unexpected, particularly considering the decline of this species in Washington, where many of these hawks rear their young.
According to Pandolfino, the decline of grassland species is a long-term and continent-wide issue. However, he also believes that there is a glimmer of hope for the persistence of these hawks.
Ferruginous Hawks in California may have managed to thrive due to several reasons. Firstly, these hawks have a preference for larger prey compared to other raptors that inhabit the same environment. This gives them an advantage as they can target prey such as the Black-tailed Jackrabbits, which are known to flourish in open habitats, including those affected by development and agriculture. Secondly, it is possible that Ferruginous Hawks have adapted and learned to utilize inactive croplands as a new source of habitat. Lastly, these hawks might have also broadened their diet to include a wider variety of prey species, further contributing to their resilience in California.
The apparent increase in the population of hawks in open habitats, despite the reduction in their natural habitats, highlights the intricacies of their population dynamics. It is crucial to understand the fate of young Ferruginous Hawks, as they face high mortality rates in their first year. Protecting the nonbreeding grounds of hawks from different age groups is essential for the long-term success of the species. In California, a collaborative and integrated conservation approach is necessary to achieve this goal.
According to Pandolofino, the vast majority of Ferruginous Hawk habitat examined in this study is located on privately-owned cattle ranches. He emphasizes that the survival of this hawk species in California is closely tied to the continued viability of cattle ranching as a means of livelihood.
Raptors like the Ferruginous Hawk play a crucial role in indicating the overall ecological well-being of their environment. In the face of our ever-changing world, this is a significant characteristic worth recognizing. Pandolfino’s ongoing research in California aims to contribute to the conservation efforts for grassland birds, particularly the Ferruginous Hawk. Additionally, he strives to raise awareness among the general public about the critical importance of preserving their rapidly declining preferred habitat.
