Ferruginous Hawks appear to select home ranges with limited human development, and with similar proportions of cropland and grassland (F2,33=10.48, p=0.0003; Figure 13). The mean proportion of cropland in home ranges is 52%, while the mean of grasslands is 48% and human development is 0.5%. The similar means, including standard error, does not show a strong selection for grasslands over croplands, and is supported by my statistical results.
Figure 13. Proportion of habitat type covering home ranges of ferruginous hawks nesting in southern Alberta (n=12). Mean proportions for cropland, grassland, and human development are 52%, 48%, and 0.52%, respectively. Letter groupings above bars represent statistically different means. Error bars represent the standard error of the data.
Grass and croplands were used significantly more than those with human development (F2,33=8.3761, p=0.001143). 51% of GPS points, or use, was found in grassland, while cropland and areas with human development were used 49% and 0.5% of the time, respectively. While grassland was used slightly more than cropland, these results were not statistically different (Figure 14).
Figure 14. Proportion of GPS points by habitat type within home ranges of ferruginous hawks nesting in southern Alberta (n=12). Mean proportions for cropland, grassland, and human development are 49%, 51%, and 0.005%, respectively. Letter groupings above bars represent statistically different means. Error bars represent the standard error of the data.
These results showed that ferruginous hawks were either using grassland or cropland, which is not surprising as southern Alberta is so highly cultivated and has pockets of grassland where it is generally not feasible to convert to cropland, such as land sections with coulees or waterbodies. The relatively equal use of cropland and grassland was stark when visualized (Figure 15). For example, if a hawk used grassland habitat ~60% of the time, it used cropland ~40% of the time. This dichotomous relationship exhibits a possible limitation for this study, as splitting the landscape into two categories does not seem to capture potential nuances in Ferruginous Hawk habitat use and likely oversimplifies habitat selection in this species.
Figure 15. Habitat use by available habitat in ferruginous hawks (n=12). The line represents a 1:1 relationship, using the assumption that the proportion of habitat that is available will have an equal proprtion of use. Data points above this line indicate the individual is using this habitat, while data points below the line indicate the individual is avoiding this habitat. Data points on the line show that the use of the habitat is equal to its availability (eg. 100% of GPS points were found in cropland, when 100% of the home range was cropland).
Only two ferruginous hawks had human development, or towns, in their home range. This provides evidence to support that ferruginous hawks avoid human development, as they are sensitive to human disturbance (Schmutz 1987). The assumption that increased cultivation leads to increased human disturbance seems realistic but appears to not have as large an impact as human density may have on ferruginous hawk habitat selection. The increased human density in towns likely increases a number of disturbance factors, such as noise and vehicle traffic, which may have more of an impact on these hawks than the loud but relatively shorter disturbance periods associated with cultivation, like seeding and harvesting with large machinery.
The home range results support findings by Ng (2019), who found that Ferruginous Hawks tend to select home ranges with roughly half grassland and half cropland, which is a change from the historic understanding that Ferruginous Hawk abundance is negatively impacted by increasing agriculture (Schmutz 1987). This may indicate that Ferruginous Hawks are adapting to this conversion of native grassland to cropland and have found ways to hunt and reproduce on this new landscape.
From these results, I can cautiously recommend that artificial nesting platforms can be constructed not only in grasslands in southern Alberta, but in cultivated fields as well. This may positively impact the Ferruginous Hawk population in Canada, as it has been found that nesting structure availability is a limiting factor to population growth (Schmutz et al. 1984, Wiggins et al. 2014). The ability to increase artificial nesting platforms in fields that have not previously provided nesting structures for Ferruginous Hawks may release some constraints on this species, leading to a greater number of breeding pairs in the province.
As these results were largely restricted by categorizing all lands used for agriculture as ‘cropland’, further analysis may indicate more appropriate recommendations. Future analyses should consider differences in crop type, as most forage crops, like alfalfa, are harvested more often than high value crops like canola. These differences in harvest frequency and timing may allow for more fine-scale changes in habitat use, where Ferruginous Hawks may increase time in forage crops as vegetation height decreases, potentially leading to easier hunting and increased predation success. This could provide evidence for managing crop rotations in a way that benefits Ferruginous Hawks nesting in the area. It will also be interesting to investigate hawk proximity to and use of oil and gas and electrical infrastructure, which provide additional perching locations for hunting and avoiding predators (APLIC 2006).