Patterns Associated with Habitat Selection by Peregrine Falcons in Central West Greenland
Type of Culminating Activity
Master of Science in Raptor Biology
Mark R. Fuller
Animals depend on habitat resources for survival and reproduction (Anderson and Gutzwiller 1994); therefore, access to adequate combinations of resources is an important determinant of the distribution and abundance of animals (Manly et al. 1993, Litvaitis et al. 1994). Habitat resources include, but are not limited to, physical characteristics of the environment, vegetation, and prey availability (Morrison et al. 1998). In 1933, Lack suggested that animals might recognize suitable habitats based on features of those habitats, and his ideas led to the concept of habitat selection. Habitat selection is the process of habitat choice by an animal (Manly et al. 1993) and can be measured when an animal uses a resource disproportionately to its availability (Johnson 1980). Habitat selection relates to habitat suitability (Krebs 1984); therefore, identifying which features are associated with selected habitats indicates which combination of features may be most suitable to those animals. An understanding of habitat choices by animals, and the cues they might use to make these choices, is fundamental to the fields of ecology, conservation biology, and natural resource management.
When evaluating habitat selection, it is common to simply assume that resources associated with selected habitats provide fitness benefits, such as better reproduction and survival rates, to the animal, but this may be misleading (Litvaitis et al. 1994, Garshelis 2000). Animals may use certain features disproportionately to their availability even if those resources do not provide measurable fitness benefits. Therefore, while habitat selection studies may identify those features associated with the animal's environment, researchers need to evaluate the fitness benefits associated with selected habitats to identify features that may be important in the quality of a habitat (Van Home 1983).
Scale is also an important consideration in habitat selection studies (Johnson 1980, Wiens 1989, Bissonette 1997). Factors important in selection may vary at different scales, and the level of selection directly affects the results and interpretation of a study (Litvaitis et al. 1994). For example, the features important for selection of the geographic range of a species may be different from the features important for nest-site selection. Although selection on all levels is ultimately important in regulating the abundance and distribution of animals, nest sites are a critical portion of a species' habitat and represent a focal area for measuring resources (Martin 1998). For birds with specialized nesting requirements, the availability of suitable nesting habitat is often one of the most important factors limiting their densities (Newton 1998). Therefore, researchers frequently measure nest site features in studies of bird-habitat associations (see Runde and Anderson 1986, Grebence and White 1989, Gainzarain et al. 2000).
Habitat quality, like selection, varies among geographic locations (Cade 1960, Newton 1998). A species such as the ubiquitous peregrine falcon (Falco peregrinus), which breeds on every continent except Antarctica, may have different requirements for suitable and quality breeding habitat in different geographical areas. Peregrine falcons are usually cliff nesting specialists and opportunistic predators (Ratcliffe 1993). In arctic central West Greenland, the Greenland Peregrine Falcon Survey (GPFS) routinely collected occupancy and productivity data on breeding peregrine falcons between 1972- 1999. Meese and Fuller (1987) studied passerines, the primary prey of peregrine falcons in central West Greenland, and presented evidence that prey density at the base of the nest cliff probably does not limit peregrine falcon breeding densities in this area. Therefore, in this thesis, I evaluated physical features associated with cliff-site selection by peregrine falcons in central West Greenland because availability of suitable breeding sites is probably more important in regulating the density of nesting peregrine falcons than prey availability. My goal was to identify habitat features that peregrine falcons may use to recognize suitable and good quality breeding sites. Environmental contamination caused the general decline of many peregrine falcon populations during the middle part ofthe 1900's (Hickey 1969, Cade et al. 1988). GPFS data suggest a population low for peregrine falcons in central West Greenland in the late 1960's or early 70's (Mattox and Seegar 1988). When Gould and Fuller (1995) analyzed occupancy data from this study area, they determined that this population was increasing, at least between 1983 and 1991. Using the 28 years of data on this expanding population, I had the opportunity to analyze patterns of peregrine falcon occupancy and distribution among suitable cliff sites, and evaluate whether productivity was associated with these patterns.
In the following three chapters I present this research and models for the practical application of my results by natural resource managers. Data from my 1998 and 1999 seasons only were used in Chapters 1 and 2. I collected additional data in 2000. I used these data, in Chapter 3, to evaluate the accuracy of my predictive model from the first chapter.
In Chapter 1, I evaluated the spacing around occupied cliff sites to determine if unused cliffs were unsuitable, or merely unavailable. I then measured habitat features at cliff sites occupied and unused by peregrine falcons and used logistic regression to determine which habitat features may be important in selection of a cliff site. I suggest some biological benefits of these habitat features to peregrine falcons, but from these data, I do not imply that cliff-site selection is a result of fitness benefits provided by certain habitat features.
In Chapter 2, I evaluated fitness benefits, using productivity data, associated with occupied cliff sites. I compared productivity associated with traditionally and recently occupied cliff sites to determine whether traditionally occupied cliff sites provided the occupants with increased fitness benefits. I also used this comparison to identify the distribution pattern in which peregrine falcons in this increasing population reoccupied their breeding habitat. I compared productivity at consistently and inconsistently occupied cliff sites to determine whether peregrine falcons used cliff sites with better reproductive benefits more consistently. I then used logistic regression to identify habitat features associated with the better quality cliff sites. Finally, I compared habitat features associated with quality cliff sites to those associated with suitable cliff sites to determine whether unused cliff sites may be unsuitable because of low fitness benefits associated with their physical features.
To conserve wildlife populations, managers must manipulate or protect habitat and this involves an understanding of the habitat resources important to wildlife populations (Garshelis 2000). In Chapter 3, I used the habitat features important for predicting suitable cliff sites to create a management model using logistic regression to predict the likelihood of peregrine falcons occupying a cliff site. I tested the accuracy of this management model using independent data reserved from an area north of the main study area. I also used habitat features important in cliff-site quality to create management models using logistic regression to predict the likelihood of traditional occupancy at a cliff site.
To summarize my research, I present evidence that unused cliffs are unsuitable irrespective of their availability. I identify habitat features that may be important in cliff- site selection, and those features that may indicate good quality breeding sites. I determine the distribution pattern in which peregrine falcons reoccupied their breeding habitat, and whether traditional and consistent occupancy of a cliff site provides productivity benefits to the occupants. I also present evidence that unused cliff sites may be unsuitable because of low fitness benefits associated with their habitat features. I conclude this research by presenting models· for the application of my research to wildlife conservation.
Wightman, Catherine Strahl, "Patterns Associated with Habitat Selection by Peregrine Falcons in Central West Greenland" (2001). Boise State University Theses and Dissertations. 449.