Ferruginous Hawk movements respond predictably to intra-annual variation but unexpectedly to anthropogenic habitats

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Animal movement is driven by a suite of processes acting across a variety of spatial and temporal scales (Nathan et al. 2008).For example, across the annual cycle, migratory species travel widely between well-dispersed areas (Klaassen et al. 2014) and even nonmigratory animals tend to show intra-annual variation in movement behaviours (van Beest et al. 2013).Birds, for example, are exposed to different sets of processes and stressors during breeding, migration and non-breeding periods (Sillett & Holmes 2002).Despite this, monitoring of many migratory species is typically limited to only one of these annual periods (Morrison et al. 2013, Marra et al. 2015).That said, understanding threats and limits to populations throughout the annual cycle is important to guide conservation measures, especially for migratory species (Sillett & Holmes 2002, Klaassen et al. 2014, Marra et al. 2015, Schuster et al. 2019).As such, by collecting movement data on birds, we can begin to understand and manage their interactions with the landscape and climate across large spatial scales (Braham et al. 2015, Wilmers et al. 2015, Wallace et al. 2016, Miller et al. 2017, Phipps et al. 2019).
Remote tracking has advanced our understanding of the movement ecology of motile species (Kays et al. 2015, Katzner & Arlettaz 2020), in part by removing many of the biases associated with historical tracking methods (van Eeden et al. 2017).For example, access to resources is a major driver of animal movement behaviour and use of space (Tucker et al. 2019) and tracking bias can influence our understanding of resource use (Silva et al. 2017).Similarly, home-range, the area where activities such as foraging, breeding and rearing young occur (Burt 1943), is often evaluated to identify habitats relevant to the survival of a species.Therefore, unbiased estimates of intra-annual variation in homerange size can help to inform understanding of which factors are correlated with long-term population stability.Improving home-range estimates during all times of the year is also useful because knowing the size and location of home-ranges can help to assess responses to intra-annual changes to the natural environment.Variation in home-range size can be driven by several factors that allow an animal to meet its energetic and ecological requirements (Burt 1943).For birds, these factors often include availability of food as well as nesting, roosting and perching sites (Miller et al. 2017).In some cases, human influence may alter the distribution of these resources in the landscape and provide resources that alter the foraging behaviour, geographical distribution and population dynamics of animals (Hidalgo-Mihart et al. 2004, Newsome et al. 2015, Petroelje et al. 2019, Marcelino et al. 2022).
Ferruginous Hawks Buteo regalis are diurnal raptors that occupy arid grasslands, shrub-steppe and highaltitude deserts across western North America, from Canada to Mexico (Giovanni et al. 2007, Ng et al. 2020, 2022).In the Intermountain West region, Ferruginous Hawks are highly dependent on ground squirrels (Sciuridae spp.) and other small rodents for food (Schmutz & Fyfe 1987, Giovanni et al. 2007).Like some other raptor species, Ferruginous Hawks have been known to exploit human-altered habitats, such as croplands that support high levels of rodent prey availability (Leary et al. 1998, Panek & Hušek 2014, Herring et al. 2020).Southern populations of this species may be sedentary or migrate short distances, whereas northern populations are typically medium-distance migrants (Ng et al. 2020).Ferruginous Hawk migration is typically non-linear, with birds first migrating longitudinally, possibly responding to variation in rodent abundance, before completing their migration south (Ng et al. 2020).This raptor species is classified as vulnerable, imperilled or critically imperilled in 18 of the 21 states and provinces across its range in the United States and Canada (Nat-ureServe 2021), and as a 'Type II Special Status Species' by the Idaho Bureau of Land Management (BLM).In most cases, habitat alteration has been suggested as a possible driver of population declines (Travsky & Beauvais 2005, Ng 2019).As with many species, Ferruginous Hawk ecology has been widely studied during the breeding season but knowledge is limited for other periods of the annual cycle.
We evaluated expectations about animal movement with data collected from Ferruginous Hawks breeding in southwest Idaho, USA.Our overall goal was to better understand patterns of movement ecology and use of space by this species across the annual cycle.Theory predicts that during the nesting season, territorial, breeding individuals should use less space than non-breeders, that animals may vary their movements in response to anthropogenic habitats, and finally that movement behaviour should respond to intra-annual variation in both internal and external factors (e.g.cycles in breeding behaviour and availability of food resources).To test these predictions, we estimated variation in home-range size of Ferruginous Hawks across months and in response to potential intrinsic (sex, age) and extrinsic (land cover and seasonal) drivers.

Study site
We studied Ferruginous Hawks that nested or hatched within the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA), in the state of Idaho, USA (Fig. 1a).Historically the NCA was dominated by Artemisia spp.shrubsteppe.However, due to wildfires, much of the NCA has been converted to open habitats dominated by native grasses and exotic annuals (Pilliod et al. 2017).Agricultural practices have also altered the landscape, with 5-6% of the NCA containing irrigated croplands (Stuber et al. 2018).At this site, Ferruginous Hawks typically arrive on territories during March before laying eggs in mid-April (Howard 1975).Nestlings typically fledge in June and all birds depart from the natal site, usually travelling to Canada, in late July-August.

Capture and GPS data collection
We considered two age-classes of birds: free-flying territorial adults captured near nests (hereafter adults) and non-territorial firstand second-year birds captured as non-flighted nestlings (hereafter juveniles).No birds captured as nestlings were observed to hold a breeding territory.
To capture free-flying Ferruginous Hawks, we used mist-nets and a robotic Great Horned Owl Bubo virginianus lure placed near the nest (Jensen et al. 2019).We captured nestlings by hand in the nest or on the ground immediately after fledging.Birds were fitted either with 30-g CTT-1030-BT3 Series GPS-GSM telemetry devices (Cellular Tracking Technologies, Rio Grande, NJ, USA) or 22-g Argos/GPS solar-powered Platform Transmitter Terminal (PTT; Microwave Telemetry, Inc., Columbia, MD, USA; Bird & Bildstein 2007).We attached transmitters with Teflon ribbon in a backpack-style harness and followed published guidelines ensuring that the mass of the telemetry unit and harness was not > 3% of the bodyweight of the animal (Steenhof et al. 2006, Bird & Bildstein 2007).The GPS-GSM units were programmed to collect GPS locations, altitude, speed, fix quality (2D or 3D fix), and horizontal and vertical dilution of precision (HDOP and VDOP) at 15-min intervals during daylight hours throughout spring, summer and autumn months.During winter, interval length was increased (up to 6 h) due to reduced solar energy limiting recharging of batteries.The Argos-PTT units were programmed to collect GPS locations, altitude, speed and fix quality at 3-h intervals, year-round.
Data collected were sent to a server via the GSM mobile phone network once per day, or via Argos satellites several times per week.Prior to analysis we removed poor quality GPS points indicated by 2D fix quality (Poessel et al. 2018).For GPS-GSM units, we also removed points for which the horizontal or vertical dilution of position (HDOP or VDOP) was > 10 (D'Eon & Delparte 2005).We calculated user equivalent range errors (UEREs) from GPS points collected while devices were in a static position for a period of 17-30 days using the ctmm package in R (GPS-GSM UERE: horizontal = 1.76; vertical = 3.08; PTT UERE: horizontal = 2.25; vertical = 1.97;Noonan et al. 2019; R Core Team 2021).We calculated the start and end of the daylight period for each GPS location using the suncalc package in R (Thieurmel & Elmarhraoui 2019, R Core Team 2021) and we excluded fixes that were collected after sunset but before sunrise.

Monthly home-range size and land cover
We estimated home-range area for each bird in each month, using autocorrelated kernel density estimators (AKDEs) implemented in the ctmm package in R (Fleming et al. 2015, Calabrese et al. 2016, R Core Team 2021).AKDEs incorporate movement effects by fitting models to GPS data to estimate an autocorrelation structure.Calculating bird home-range for each month allowed us to evaluate changes in home-range size throughout the annual cycle, as well as to compare home-range size between seasons.AKDEs are also useful because they control for irregular and uneven sampling rates.We calculated individual home-ranges for birds captured as juveniles once they settled (see below) > 100 km from their nestsite (typically after August).All periods of migration, including short migratory stopovers, were excluded from any analysis.
The ctmm package requires range residency to calculate home-ranges.Therefore, prior to any analysis, we determined range residency using visual checks for asymptotic behaviour of semi-variograms produced by the ctmm package (Calabrese et al. 2016).We identified and removed outlier telemetry locations using the outlie() function in ctmm and the associated core deviation and speed plots (Noonan et al. 2019).We only estimated home-range for bird-months where birds were range resident for ≥ 8 days and with ≥ 30 GPS points (Braham et al. 2015;Fig. 2b).During those months where birds were only partially range resident (i.e.spent a portion of the month wandering), we estimated home-range using only the days when the bird was range resident.When birds established range residency in more than one area within the same month, we used the separate home-range estimates to calculate a mean that we weighted by the duration spent in each home-range.
We used the variogram.fit()function in ctmm to identify starting values for model parameters (following Calabrese et al. 2016; see below for description of parameters).The ctmm package allows testing models with a suite of different distributional assumptions.Therefore, for each bird-month, we fit and compared all possible movement models available in this package (see Calabrese et al. 2016 for details of the different movement models available in the ctmm package).We selected the most appropriate model via the Akaike information criterion corrected for small sample sizes (AICc).We then calculated the final 95% ADKE using the movement model with the lowest AICc value for that birdmonth.
We assessed land-cover association within home-ranges across the annual cycle.To characterize land-cover types within each home-range, we imported into R the home-ranges and associated land-cover information from the 2015 North American Land Cover dataset, which has a resolution of 30 m 2 (Commission for Environmental Cooperation 2015).We then used the raster package (Hijmans et al. 2021) to calculate the proportion of each land-cover type (Barren, Cropland, Temperate Grassland, Temperate Shrubland, Urban, Water, Wetland, Forest, Tropical Grassland and Tropical Shrubland) within each home-range.

Statistical modelling
We evaluated intra-annual (monthly) variation in home-range size throughout the year using a generalized additive mixed model (GAMM; R package mgcv; Wood et al. 2016).Fixed effects in the model were age and sex, and random effects were individual bird identity.We tested model performance with and without a random effect for year, to account for response of birds to year-to-year variation.We fitted a cyclic smoothing spline to the month term in the model to capture nonlinear relationships associated with this term.As our data were continuous and zero-bounded, we used the Gamma error family with a log link function.As the timing of migration by these hawks was variable, we evaluated seasonal variation in home-range size during months where birds were exclusively within the breeding range or winter ranges using a generalized linear mixed effects model (GLMM; lme4 package in R; Bates et al. 2015).The fixed effect in the model was season (3 months each, either breeding (April-June) or wintering (November-January)).Random effects were individual bird identity and year.We again used the Gamma error family with a log-link function.
We evaluated the relationship between homerange size and land-cover types within those home-ranges with two GLMMs.We built separate models for the months in which we had breeding (March-July) and non-breeding (August-February) season home-ranges (these are slightly different months from those in the prior analyses because this analysis included short periods of residency in autumn).For the breeding season, we included fixed effects for proportions of two land-cover types, cropland and grassland (as defined by the 2015 North American Land Cover dataset noted above).During the breeding season, three landcover typescropland, grassland and shrublandwere most widely available within home-ranges.Shrubland was excluded as a fixed effect, as values of this variable were highly positively correlated with grassland.Bird identity again was included as a random effect in the model.For months spent exclusively in the breeding territory (April-June), we also used a linear regression to test the relationship between mean home-range size of birds and distance from the nest to the nearest cropland.
When not on breeding grounds, land-cover types present within home-ranges were highly variable among birds, and, within home-ranges, we detected correlations in proportional cover of many land-cover types.As such, to focus on the role of anthropogenic habitats on birds, we included in our models only one fixed effect, proportion of cropland, with bird identity as a random effect.In both models, we again used the Gamma error family with a log-link function.

RESULTS
We considered GPS data from 12 Ferruginous Hawks, eight adults (five female and three male) and four juveniles (two female and two male), captured in the NCA during May-June 2016-2019, and tracked over the subsequent months (Supporting Information Table S1).Over the study period (May 2016 to April 2021) we collected 185 941 high-quality GPS locations during daytime (Fig. 1b).The duration of tracking for individual birds ranged from 1 to 45 months.After removing bird-months for which data were sparse, we estimated home-ranges for 207 bird-months (details on sample sizes by month are provided in Supporting Information Table S2).

Monthly home-range size and landscape predictors
The monthly 95% home-range sizes of Ferruginous Hawks varied across the entire annual cycle and ranged from 0.06 to 4085.41 km 2 , averaging 191.39 AE 34.37 km 2 (AE se; n = 12 birds and 207 bird-months; Fig. 1c, Supporting Information Table S3).Monthly home-range size of adults during the breeding season (March-July) ranged from 0.01 to 3723.59 km 2 (115.81AE 55.94; n = 10 birds and 76 bird-months), and outside of the breeding season (August-February) from 0.55 to 4085.41 km 2 (223.96AE 50.05; n = 9 birds and 106 bird-months).Monthly home-range size of juveniles during the breeding season ranged from 0.35 to 1295.43 km 2 (207.70AE 158.03; n = 3 birds and 8 bird-months).Monthly home-range size of juveniles outside of the breeding season ranged from 7.97 to 1476.34 km 2 (318.49AE 94.46; n = 4 birds and 17 bird-months).
There was a non-linear association between month and average home-range size (i.e. the spline of month was highly significant for adult hawks; effective degrees of freedom (edf) = 4.94, ref df = 8, F = 14.71,P < 0.001; Fig. 2a) but not for juvenile birds (edf = 0.71, ref df = 8, F = 0.13, P = 0.22; Fig. 2a).Home-range size of adult Ferruginous Hawks was smallest during the breeding season months of May (2.59 AE 1.01 km 2 , x AE se, n = 8 birds and 15 bird-months), June (9.65AE 2.26 km 2 , n = 10 birds and 21 bird-months) and April (24.94AE 23.18 km 2 , n = 8 birds and 13 birdmonths; Fig. 2a).In contrast, empirical means of home-ranges were largest during July (412.52AE 216.78 km 2 , n = 9 birds and 20 bird-months) and October (277.54AE 119.50 km 2 , n = 9 birds and 19 bird-months; Fig. 2a).Overall, home-range size in the 3 months of the breeding season (April-June) was significantly smaller than during the 3 months of the wintering season (November-January; P < 0.001).Monthly home-range size of Ferruginous Hawks was not different among the sexes (P = 0.46; Table 1).Including a random effect for year reduced model performance and so we did not consider this term in our modelling efforts.
There were six land-cover types within the home-ranges we estimated for the months between March and July (when known, arrival and departure dates to and from the breeding ground were 5 January to 21 March and 11-28 July, respectively; Fig. 2c).The most abundant land-cover types were Temperate Grasslands (x = 58.24%),Temperate Shrublands (x = 40.98%)and Croplands (x = 0.68%; Table S4a).When on non-breeding range (arrival dates on non-breeding grounds ranged from 16 July to 21 February and departure dates ranged from 27 December to 5 March; Fig. 2c), Ferruginous Hawks were range resident in a huge diversity of areas (n = 47 home-range areas spanning from 26.138°to 51.285°N latitude) throughout the USA, Mexico and Canada.Within those homeranges there were 12 land-cover types available in the landscape, with Temperate Grasslands and Croplands being most abundant (x = 46.48% and x = 36.14%,respectively; Table S4b).
Cropland was an exceptionally good predictor of variation in monthly home-range size of Ferruginous Hawks.During the nesting season, although hawks were only associated with small amounts of cropland, this cover type was strongly positively associated with monthly home-range size (β = 37.01, t = 4.51, P < 0.001; Table 1, Figs 1c  and 3a).There was a weak positive correlation between monthly home-range size of adult birds during the breeding season months and distance to the nearest area of cropland (r = 0.36; P = 0.153).Grassland was also positively associated with home-range size during the breeding season (β = 3.84, t = 3.33, P < 0.001; Table 1).In contrast, outside of the breeding season, hawks were associated with larger quantities of cropland, but this cover type was strongly negatively associated with home-range size (β = −1.86,t = −3.35,P < 0.001; Table 1, Fig. 3b).

DISCUSSION
It is not surprising that the home-range of these hawks varied across the annual cycle, and these types of responses have been widely documented in the literature (e.g.Braham et al. 2015, Miller et al. 2017).General movement behaviour of our hawks was also similar to that reported previously Table 1.Models evaluating variation in size of home-ranges of Ferruginous Hawks from the Morley Nelson Snake River Birds of Prey National Conservation Area, Idaho, 2016-2021.Generalized additive mixed models were run to explain the influence of (a) sex and month on home-range size (monthly 95% autocorrelated kernel density estimation (AKDE), n = 12 hawks and 207 bird-months).Generalized linear mixed-effects models were used to explain influence of (b) season on home-range size (95% AKDE) of breeding adult hawks; and the influence of land-cover type on monthly home-range size (95% AKDE) of (c) territorial Ferruginous Hawks during the breeding season (n = 8 hawks and 58 bird-months); (d) and all hawks during the non-breeding season (n = 11 hawks and 119 bird-months).Sex comparisons use female as the reference level.for this species (Leary et al. 1998, Watson 2003, Watson 2020, Kocina & Aagaard 2021).In contrast, although movement responses of wildlife to anthropogenic habitats have also been well studied (Lanszki et al. 2018, Main et al. 2020, Todorov et al. 2020), the seasonal variation we observed in movements in relation to cropland was unexpected.The contrast between these expected and unexpected movement patterns thus provides important insight into the drivers of movement for these and other species which may select for anthropogenic habitats.

Documenting the expected
Ranging behaviour of animals is expected to respond to intrinsic factors such as age, sex and breeding status, as well as extrinsic factors such as seasonality and resource availability.Our analyses tested for both types of factors.The patterns we observed, with the smallest home-ranges during the months of the breeding season and larger home-ranges at other times of year, fit our expectations for how territorial and migratory species typically behave.Similar to other raptor species, adult Ferruginous Hawks appeared as central place foragers that stay close to the nest-site during breeding months, presumably to defend their territory and rear their young (Watson 2003, 2020, Moss et al. 2014, Miller et al. 2017, Ng et al. 2020).In contrast, and again consistent with our expectations, younger and apparently non-territorial hawks were not tied to a specific nesting site and therefore had larger home-ranges.Although we restricted analyses to periods of residency, larger homeranges of non-territorial birds may still be associated with a higher degree of local wandering and exploration for potential breeding sites (Miller et al. 2017, Watson et al. 2019, McCabe et al. 2021).The larger home-ranges we observed outside of the breeding season could have been linked to reduction in habitat quality due to changes in factors such as prey availability (Moss et al. 2014, Mirski et al. 2021) or a reduction in defensive behaviour and sharing of resources (Grande et al. 2009).
There are two notable caveats to our inference regarding response to these resources.First, we were not able to test how variation in food availability between years may have influenced movement of these hawks.We expect that during years with less abundant food resources, home-range sizes would be larger.Secondly, we did not detect sex-specific differences in home-range size of these birds.Such differences have been detected for some adult raptors (female Red Kites Milvus milvus and Golden Eagles Aquila chrysaetos have larger home-ranges than did the males; Braham et al. 2015, Spatz et al. 2022; male Montagu's Harriers Circus pygargus have larger home-ranges than do the females; Krupi ński et al. 2021) but not for others (Golden Eagles in Miller et al. 2017).In this case, it is unclear exactly what factors may have resulted in the lack of sex-related differences in ranging behaviour.

Documenting the unexpected
Animals sometimes travel long distances to reach specific natural resources.For example, African elephants Loxodonta spp.and other mammals travel to access essential minerals found in salt licks (Lameed & Adetola 2012).Similarly, bats are known to travel long distances through landscapes dominated by cropland to access sparsely distributed patches of natural woodland or riparian habitats (Kniowski & Gehrt 2014).However, it is less commonly documented that those increases in movements are motivated by anthropogenic habitats, as we observed here.In fact, anthropogenic habitats often result in a contraction of homeranges, as animals restrict their movements to utilize small patches of the landscape with atypically dense resource availability (Petroelje et al. 2019).In a similar vein, Red Kites in the UK may travel away from roosts and breeding sites to forage at locations where supplementary feeding occurs (Orros & Fellowes 2015).
The territorial Ferruginous Hawks we studied frequently visited small parcels of irrigated cropland.However, as noted previously in southcentral Washington during the breeding season (Leary et al. 1998), they travelled surprisingly long distances to access those parts of the landscape.This increased the size of their home-ranges.Irrigated croplands provide perches, low vegetation density and high rodent populations for some raptors during certain parts of the year (Panek & Hušek 2014, Ng 2019, Zagorski & Swihart 2021).As Ferruginous Hawks are rodent specialists (Schmutz & Fyfe 1987, Giovanni et al. 2007, Ng 2019), we suspect that the cropland they were using may be an anthropogenic subsidy for these birds, Specifically, we suspect that they were exploiting agricultural areas with high-density prey populations or increased hunting opportunities, as has been seen for other raptors (Panek & Hušek 2014, Herring et al. 2020).All that said, our analyses and understanding of key data on crop type, levels of irrigation and foraging success are insufficient to draw strong inferences in this regard.
The explanation for this atypical behavioural response to an anthropogenic habitat may lie in the details of the breeding biology for this species and specific features of our study site.Ferruginous Hawks are, in general, nest-site limited (Wallace et al. 2016).Typically, these birds build nests on natural substrates such as trees and cliffs or on elevated anthropogenic structures, although they may also nest on the ground where elevated sites are not available (Wallace et al. 2016, Ng et al. 2020).In our study area, land managers have created a large number of artificial nesting platforms that were used by all the territorial Ferruginous Hawks that we tagged.Furthermore, only some of these platforms are located near agricultural lands.That said, nearly all of the hawks that we tracked made trips, apparently for foraging, to agricultural habitats (Fig. 1b,c).Therefore, the desire to use two anthropogenic resources, nesting platforms and croplands, probably created the atypical response that we observed, with most birds accessing croplands, whether their nest platform was close to or far from that cover type.The fact that they sometimes did not use the closest agricultural landcover also probably explains why we only detected a weak relationship between distance to cropland and home-range size.This proposed explanation for the atypical response to cropland we observed also helps us to understand why the hawks we studied showed the more typical pattern in winter, having smaller home-ranges when centred on agriculture.Winter habitat of Ferruginous Hawks includes the edges of agricultural land which support an abundance of rodent prey (Watson 2003, Ng et al. 2020).During the non-breeding season, these hawks have no need for artificial nest platforms and thus, unlike in the nesting season, their movements are exclusively in response to a single anthropogenic resource.Understanding how Ferruginous Hawks show intraannual change in their response to cropland therefore provides important insight into the nuance of this human-wildlife interaction.It may therefore be useful to ask whether this nuance extends to other species of conservation concern, particularly those which simultaneously utilize more than one anthropogenic resource.
Improper placement of artificial nesting structures may result in structures remaining unoccupied or being associated with low productivity (Catry et al. 2011, Gottschalk et al. 2011).For Ferruginous Hawks, and other species which utilize these nesting platforms, it may therefore be beneficial to construct platforms closer to the habitats in which they are exploiting resources.This pattern will probably hold true for other raptor species that specialize on rodent prey and that are associated with cropland.In our study area, such species may include Red-tailed hawks Buteo jamaicensis and Swainson's Hawks Buteo swainsoni (Coates et al. 2014).However, it should be noted that not all types of croplands will impact raptors in the same way (Assandri et al. 2022).Furthermore, although the cropland in our study appeared to allow hawks to forage successfully during breeding season months, crops that increase in height and density over the course of a season may reduce the ability of hawks to catch prey (Panek & Hušek 2014, Rodríguez et al. 2014).

CONCLUSIONS
This is said to be a golden age of animal movement studies (Kays et al. 2015).Although Ferruginous Hawks are widespread in western North America, their biology is poorly understood.The novel tracking technologies we deployed to track these birds, in combination with detail on the environment they occupied, provided new insight into their behaviours.Most, but not all, of the relationships we documented were those that theory would predict and were consistent with previous study of this species.The unexpected behaviours therefore provide important insight into how Ferruginous Hawks prioritize resources on the landscape and how human activity, in this case providing two simultaneous resources, can influence the ecology and movements of these and potentially other wildlife adapting to anthropogenic alterations to the landscape.
A large number of people assisted in work to trap and telemeter the hawks studied in this project.Terry Bennet manufactured the mechanical owl used in trapping.Steve Alsup, Joe Weldon, Talia Jolley, Jamie Yurick, Ariana Dickson and many others provided crucial information on nest occupancy.James Belthoff played a crucial role in organizing the university placement that made this research possible.The Katzner lab provided feedback on early versions of the manuscript.J. Ng, an anonymous reviewer, associate editor W. Vansteelant and editor R. Kimball provided useful reviews of the manuscript.The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Figure 1 .
Figure 1.(a) GPS locations of two Ferruginous Hawks (solid and dashed black lines) tracked from breeding locations in southwest Idaho for one full annual cycle across North America.Both birds initially moved north from breeding grounds following the direction of the arrows.Star symbol indicates the capture site at the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA), Idaho.(b) GPS fixes of all individuals (n = 12) tracked throughout their breeding area in the NCA.Dark grey patches show the distribution of cropland and black box shows area in (c), data from a single individual tracked throughout the NCA during one breeding season, illustrating this bird's main area of use around the nest, with excursions to those croplands.Black lines indicate the autocorrelated kernel density estimate of home-range boundary with 95% confidence intervals for 1 month of movement.

Figure 2 .
Figure 2. (a) Generalized additive mixed model and 95% confidence intervals showing effect of month on mean monthly homerange of Ferruginous Hawks (95% autocorrelated kernel density estimation, n = 12 hawks (eight captured as adults, four captured as juveniles) and 207 bird-months) tracked between 2016 and 2021 in North America.(b) Number of days analysed where birds were range resident for each month.(c) Distance of home-range areas from the breeding site (NCA) for each month analysed.

Figure 3 .
Figure 3. Effects of proportion of cropland within the homerange (95% autocorrelated kernel density estimation) on home-range size of Ferruginous Hawks inside and outside of the breeding season.(a) Breeding adult hawks during the breeding season (March-July) and (b) range resident hawks outside of the breeding season (August-February).The shaded area represents the 95% confidence interval around home-range size.