Owl and Hawk Adaptation to Urban Centers

JUST, Vol. IV, No. 1, 2016 Trent University

Urban Raptors: Owl and Hawk Adaptation to Urban Centers

Matthew Poppleton

Abstract This report focuses on the adaptation of raptors, speciﬁcally hawks and owls, to urban environments. Sighting data was gathered from 3 online sources using Peterborough based data. In the city of Peterborough, the broad-winged, red-tailed, sharp-shinned hawks (Buteo platypterus, Buteo jamaicensis, and Accipiter striatus respectively) and the great gray and great horned owls (Strix nebulosi and Bubo virginianus respectively) are recorded in high numbers relative to other species. The ability for raptors to adapt to urban settings is dependent on ecological limiting factors, including prey items and habitat availability. Many owls and hawks seem to adapt well to urban settings, however there are variances within species and local-populations. Maintaining sufﬁcient natural resources within urban centers is necessary to conserve healthy raptor populations. Keywords Ecology — Ornithology — Environmental Science

Introduction Audubon Society’s eBird, the Peterborough Field Naturalist’s Christmas Bird Count (CBC), and the Atlas of the Breeding The ecology of urban wildlife is a relatively recent research Birds of Ontario (ABBO). This section discusses the different field, which aims to provide wildlife conservationists and sources and their methodologies. managers with knowledge of how animals respond to urban environments. This information can also be used by city The website eBird.com is a citizen science tool, in which planners to build and maintain effective resources and devel- individuals, organizations, and publications with registered opments to facilitate the continued use of urban centers by online accounts can input bird species sightings from certain animals. In this report, raptors, specifically owls and hawks, locations including Peterborough (eBird.org 2016a). The bird are of interest because they are a charismatic species that count and date is included with each recorded sighting, along people have admired for millennia (Kaufman 2000). Urban with options of photos and notes. Sighting totals for each wildlife management is more effective when focusing on a species are not available so the individual highest counts of species that citizens want to protect. Protecting and managing each species from specific dates are used instead. This source these raptor species also necessitates the protection of wildlife of sightings is particularly useful for urban birds because that raptors depend upon, species which otherwise may be individuals can enter sightings from any location within the thought of as pests, including small mammals, rodents and city (eBird.org 2016a); the other sources can only record birds birds. from set locations within the city. An issue with eBird is This article contains a primary report and a literature re- that although historical dated sightings are available, active view. The primary report provides sighting data on owls and citizen science records only begin around 2012-2013, creating hawks within Peterborough, Ontario, and discusses the find- a disproportionate amount of recent sightings to past sightings ings. The literature review discusses the current and past (eBird.org 2016b; 2016c; 2016d). literature on raptor adaptation to urban centers with respect to habitat and diet; urban hazards and recommended man- Another source of data are The Peterborough Field Natu- agement directions are also discussed. The report aims to ralist’s (PFN) Christmas Bird Count (CBC), a local chapter be relevant to Peterborough, however these implications are of The National Audubon Society’s data collection (Peter- relevant for other urban centers as well. boroughnature.org 2015a). The sighting data is recorded by registered groups of volunteers located at separate locations 1. Primary Report: Peterborough Hawk along a 24 km diameter within Peterborough County during and Owl Sightings one day in December (Peterboroughnature.org 2015b). It should thus be noted that each year records one day’s worth 1.1 Methods: Raptor Sighting Sources of sightings. Online data is available from the Audubon So- I collected hawk and hawk sighting information from three ciety from 1900-2014 (Netapp.audborn.org 2016). I totalled separate sources: the Cornell Lab of Ornithology and National sightings over the past 20 years. Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 2/12

The Atlas of the Breeding Birds of Ontario (ABBO) record counts from all three Peterborough sources (Table 2). Red- uses a point count system in which birds are counted within tailed hawks have been described as “the most seen hawks in specific regions. The dataset includes information on breeding Ontario” by Bezener (2000) which may explain the consis- evidence and various point count indices, and so the method- tently high counts (p 97). The sharp-shinned hawk is the third ology may be more systematic than the CBC and eBird; how- most recorded hawk for Toronto and Peterborough, but neither ever, I did not find the actual methodology used. ABBO’s data of these counts are considerably high (Table 3). The red-tailed is more limited by time than the other two sources because hawk and sharp-shinned hawk are rated as a potential urban it only has data available from 1981-1985 and 2001-2005 resident with 3/3 points of degree of urban use, whereas the (Birdsontario.org 2016). Also, ABBO and the CBC may broad-winged hawk is only rated a regular user with 2/3 points be more representative of species within specific areas than (Table 2; Hager 2009). All three of these hawks use urban eBird, because they show trends for birds appearing within areas for the winter, migration and breeding (Table 2; Hager set locations, however, they have limited timescales. eBird 2009). The Cooper’s hawk (Accipiter cooperii) is also a po- is not restricted by time, since the birds can be located any- tential urban resident with a 3/3 score of urban use, but does where within Peterborough at any time, and the boundaries are not have high sighting counts (Table 2; Table 3; Hager 2009). much larger than the plots of the CBC and ABBO. Since each Also, the gray hawk’s (Buteo plagiatus) 2 sightings in Peter- of the sources used have different timescales and recording borough from the CBC are likely misidentifications, because methodologies, the counts cannot be totaled to show anything the gray hawk is a tropical species of southern North America in particular other than the relative number of owl and hawk and South America (Allaboutbirds.org 2016b). The 1 Swain- sightings in Peterborough. son’s hawk (Buteo swainsoni) sighting in Toronto may also be a misidentification, because its normal distribution, similar to the gray’s hawk does not extend to Ontario (Allaboutbirds.org 1.2 Sighting Data and Discussion 2016c). Before synthesizing the results, it needs to be understood that The owl species sightings are all below a count of 100, all of the recording methods only demonstrate the number of and do not follow any location trends (Table 2; Table 3). The birds that can be recognized by the recorders. Sightings are absence of barn owl (Tyto alba) sightings from every source likely influenced by recognizable traits, spatial and temporal and location except Waterloo (count of 1), is likely indicative flight patterns as well as and bird calls produced noise. Due of its endangered status (Ontario.ca 2016). The two owls with to these issues, the sighting data can only demonstrate the notably higher sightings from the rest of the owls are the great presence and absence of certain species; presence confidence gray owl (Strix nebulosa; 83 sightings from eBird) and the should increase with higher numbers because they are less great horned owl (Bubo virginianus; 40 sightings from the likely to be mistakes (Table 2; Table 3). The data may also CBC) (Table 2). The great gray owl likely has high counts be used as a rough estimate of urban abundance based on the because it is the tallest and has the greatest wingspan of all count of each species, however the above issues need to be North American owls and is thus relatively easy to identify taken into account (Table 2; Table 3). Additionally, informa- (Allaboutbirds.org 2016d). The great horned owl is also a tion of the relative amount of raptor urban use and degree large owl that is also easy to identify, due to the ear-like of use from Hager (2009) is included. Table 3 compares feathered tufts that on its head (Allboutbirds.org 2016e). The sighting trends across Peterborough, Toronto and Waterloo. low overall owl sightings may be more due to the difficulties of Waterloo is selected due to similarities of population size and studying owl habituation due to their quiet nocturnal activity, area to Peterborough (Table 1); there are no other urban cen- migration and habitat loss (Dykstra et al. 2012; Hager 2009). ters in Ontario similarly sized to Peterborough within eBird’s database (Statcan.gc.ca 2016a; 2016b). Toronto is included due to its massive land area and population, and its proximity 2. Literature Review and Discussion: to Peterborough (Table 1) (Statscan.gc.ca 2016c). Urban Raptor Adaptation Comparing the eBird highest counts from Peterborough with Waterloo and Toronto shows some species trends: the 2.1 Limiting Factors and Generalists/Specialists broad-winged hawk (Buteo platypterus) is the bird with the It may seem reasonable that the human disturbances, low highest hawk count for all three regions, with notably higher vegetation levels and structures associated with urban centers counts than the rest of the hawk data (Table 3). However, would limit the productivity and nesting sites of bird species; only eBird in Peterborough shows high results for the broad- however, many published studies have found that many birds, winged hawk (Table 2). The consistently high broad-winged including raptors, adapt well to urban habitats (including: hawk counts may be the result of sightings during migratory Hager 2009; Dykstra et al. 2012; Chase and Walsh 2006; periods, in which these hawks can be found in flocks with Rodewald and Kearns 2011; Stout et al. 2006; Minor et al. thousands of individuals (Allaboutbirds.org 2016a). Addition- 1993; Boksakowski and Smith 1997; Campbell 2009). ally, the red-tailed hawk (Buteo jamaicensis) has the second The ability of a species to successfully adapt to urban areas highest hawk count for all three regions (Table 3), and is is controlled by certain ecological limiting factors. Animals the only species (owl or hawk) which has consistently high living in urban areas will typically be affected by different Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 3/12

Table 1. The population and land areas of the City of Peterborough, Waterloo and Toronto, using information from Statistics Canada’s 2011 Census. Statscan.gc.ca 2016a; 2016b; 2016c respectively. Peterborough Waterloo Toronto 2011 Census Population 78,698 98,780 2,615,060 2011 Census Land Area 63.8 64.02 630.21 (km2) limiting factors than in natural areas due to altered ecosystems 2.2 Habitat/Nesting and resource availability (Adams et al. 2006). Adams et The ability of hawks and owls to habituate within urban en- al. (2006) suggest that there are generally fewer limiting vironments is suggested to be dependent on the populations factors for wildlife within urban centers than natural habitats of species rather than species alone (Dykstra et al. 2012). due to an increased abundance of resources including food, This is to say that a population of a certain raptor species may water and shelter, and decreased predator abundance. Raptors be able to thrive within some urban centers and not others. are limited by both the availability of habitat for nesting and Thus it is important to remember when reviewing the species’ food/prey resources, and may be generalists or specialists with within the literature that the success of a species population respect to both these resources (Bird et al. 1996; e.g. Rullman to colonize an urban area does not mean that all populations and Marzluff 2014). A specialist species requires certain prey of that species will colonize urban areas (Dykstra et al. 2012). to meet its dietary needs or certain habitat needs, while a However, reports concerning local population adaption may generalist is able to use a broader variety of prey/habitats be used to provide a synthesis of avian responses to urban to meet the same needs. Prey availability is influenced by environments, and more comprehensive ideas can apply to prey vulnerability and predatory access (Rullman and Marzluf broader regions. 2014). These factors shift across urban environments, and thus shift prey availability (Rullman and Marzluf 2014). Prey vulnerability is affected by many factors including foraging 2.3 Land Cover behaviour, bird feeders, breeding status/courtship behaviours, A key factor affecting of bird habitat is the land-cover type nest selection and overall landscape-based predation access (the landscape type on a regional scale: grassland, forested risks (Rullman and Marzluf 2014). Additionally, the density land, developed land, etc.). The number of bird species as- of avian nesting is limited by resource density, quality and sociated with certain habitats has been found to be higher by territorial zones from neighbouring birds – which is to say within Ottawa’s urban centers than greenbelts and some con- the amount of food, nesting site availability and competition tiguous forestland, due to greater land-cover heterogeneity (Newton 1986 as cited in Mannan and Boal 2000). within the urban areas (Campbell 2009). This is also the case Rullman and Marzluf (2014) observed that prey gener- with raptors. Stout et al. (2006) found that red-tailed hawks alist Cooper’s hawks (Accipiter cooperii) and barred owls (Buteo jamaicensis) had greater nesting use of heterogeneous (Strix varia) were able to meet dietary needs within urban and habitats, which are representative of suburban areas, than ho- forested areas with sufficient land-cover. Thus prey access mogenous habitats representative of highly developed areas. is likely interlinked with habitat factors. Specialist animal The heterogeneous nesting habitat had over three times the species are usually limited in their ability to adapt to urban amount of unused grassland and woodland land-cover for centers, due to the specific habitat and/or prey requirements nesting (Stout et al. 2006). This may imply that the red- (Gilbert 1989). Campbell (2009) suggests that the potential tailed hawk may successfully nest within Peterborough due to for specialist species to colonize greenbelts is affected by the the city’s large amount of suburban areas, surrounding green degree of similarity between greenbelt forest and contiguous spaces and inner parks. These areas may provide sufficient forests, and how recreational activities affect these species. grassland and forested land-cover for red-tailed hawks and This would likely also apply to specialist species nesting in other raptor species. urban landscapes. Thus, the similarity of urban forests to Undeveloped land-cover within urban centers can sup- contiguous forests may affect the degree to which specialist port rare urban birds (Loss et al. 2009). Thus, undeveloped species can adapt to urban habitats. Generalist species are land-cover will likely support habitat-specialist raptors. The more likely to adapt to urban environments with less strict availability of natural land-cover patches can also influence boundaries. Urban areas contain a relatively low predator the potential of migratory birds using urban habitats (Konze abundance, anthropogenic feeding, high perching availability, 2009). For information on managing urban raptor habitats see good access to water bodies along with natural land-cover ar- Literature Review: Management Implications. Raptors seem eas (Campbell 2009) and thus likely attract generalist species. to thrive within high natural and urban land-cover types, as demonstrated in western Washington (Figure 3) (Rullman and Marzluf 2014). Thus the ability for raptors to excel within Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 4/12

Table 2. Hawk sightings in Peterborough Ontario from three separate bird sighting counts. Records are from eBird’s highest individual count records; the Peterborough Field Naturalist’s Christmas Bird Count’s (CBC) totals over the past 20 years; the Atlas of Breeding Birds of Ontario’s (ABBO) records from 2001-2005. Degree of opportunity is on a scale of 1-3, representing inconsistent use, regular use and potential residency, respectively (Hager 2009). Urban activity use describes whether the bird uses urban areas for breeding (B), the winter (W) and for migration (M) (Hager 2009). N/A is included for species that are included by Hager (2009), but are not reported to use urban centers. Degree of urban activity and urban activity use are modiﬁed from (Table 1 as cited in Hager 2009, p 214) (Sightings are from eBird.og 2016b; Netapp.auborn.org 2016; Birdsontario.org 2016) Species eBird CBC ABBO Degree of Ur- Urban ban Activity Activity Use Hawk Species Broad-winged hawk (Buteo platypterus) 362 0 18 3 BWM Cooper’s Hawk (Accipiter cooperii) 3 69 1 3 BW Ferruginous hawk (Buteo regalis) 0 0 40 2 W Gray Hawk (Buteo plagiatus) 2 0 0 1 B Northern Goshawk (Accipiter gentilis) 0 11 3 1 WM Red-Shouldered Hawk (Buteo lineatus) 3 0 11 3 BW Red-tailed hawk (Buteo jamaicensis) 10 660 17 3 BWM Rough-legged hawk (Buteo lagopus) 0 7 0 N/A N/A Sharp-shinned Hawk (Accipiter striatus) 7 51 5 2 BWM Swainson’s Hawk (Buteo swainsoni) 0 0 0 2 B Owl Species eBird CBC ABBO Degree of Ur- Urban ban Activity Activity Use Barn Owl (Tyto alba) 0 0 0 2 B Barred Owl (Strix varia) 13 0 3 2 BW Boreal Owl (Aegolius funereus) 1 0 0 N/A N/A Eastern Screech-Owl (Megascops asio) 2 3 0 3 BW Great Gray Owl (Strix nebulosa) 83 0 0 N/A N/A Great Horned Owl (Bubo virginianus) 5 40 2 2 BW Long-eared Owl (Asio otus) 1 0 1 1 W Northern Hawk Owl (Surnia ulula) 1 0 0 1 BW Short-eared Owl (Asio ﬂammeus) 1 1 0 1 M Snowy Owl (Bubo scandiacus) 1 1 0 3 W Northern Saw-whet Owl (Aegolius 11 0 0 2 BWM acadicus) certain land-covers seems to be dependent on the species, duce equally well in urban and natural areas. Similarly, the population, and land-cover type. barred owl’s nesting habitat usage has been observed to be unaffected by suburban developments (Dykstra et al. 2012). This instance may be due to the owls having low interactions 2.4 Species and Population Traits with humans because of their low detectability and nocturnal Separate species sizes can also associate with separate land- activity as mentioned in Primary Report: Sighting Data and cover types. For example, in a study by Campbell (2009), Discussion (Dykstra et al. 2012; Hager 2009). Coleman et al. large birds were more commonly found within contiguous (2002) found no relationships between the quality of habitats forests than small birds. This may be due to high tree density and raptor productivity, implying that cover type may be a and low human activity (Campbell 2009). Also, generalist stronger parameter than habitat quality. Additionally, for an species were not found in the contiguous forest areas in this urban area to be a bird nesting source, it is important to have study. This may imply that larger species are generally habi- high reproductive success, nest site re-occupancy, and popu- tat specialists. Campbell (2009) suggests that bird presences lation recruitment, as observed in Milwaukee, Wisconsin, by can be well predicted using habitat types, while species pres- Stout et al. (2007). ence patterns are better explained by species type. Different communities have varying success with urban habitats and Some species have greater selectivity for certain nesting nesting. Minor et al. (1993) found that great-horned owls land-cover types. The sharp-shinned hawk (Accipiter striatus) and red-tailed hawks were able to successfully nest and repro- has been observed to nest within coniferous trees in habitats Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 5/12

Table 3. The highest recorded counts of hawk and owl populations from eBird in Peterborough, Toronto, and Waterloo, Ontario (eBird.org 2016b; 2016c; 2016d respectively). Hawk Species Toronto Waterloo Peterborough Broad-winged hawk (Buteo platypterus) 7060 1200 362 Cooper’s Hawk (Accipiter cooperii) 18 9 3 Ferruginous Hawk (Buteo regalis) 0 0 0 Gray Hawk (Buteo plagiatus) 0 0 2 Northern Goshawk (Accipiter gentilis) 0 1 0 Red-Shouldered Hawk (Buteo lineatus) 40 8 3 Red-tailed hawk (Buteo jamaicensis) 750 110 10 Rough-legged hawk (Buteo lagopus) 1 30 0 Sharp-shinned Hawk (Accipiter striatus) 646 15 7 Swainson’s Hawk (Buteo swainsoni) 1 0 0 Owl Species Toronto Waterloo Peterborough Barn Owl (Tyto alba) 0 1 0 Barred Owl (Strix varia) 2 2 13 Boreal Owl (Aegolius funereus) 2 1 1 Eastern Screech-Owl (Megascops asio) 6 37 2 Great Gray Owl (Strix nebulosa) 2 1 83 Great Horned Owl (Bubo virginianus) 6 38 5 Long-eared Owl (Asio otus) 10 10 1 Northern Hawk Owl (Surnia ulula) 1 1 1 Northern Saw-whet Owl (Aegolius 4 2 1 acadicus) Short-eared Owl (Asio flammeus) 15 5 1 Snowy Owl (Bubo scandiacus) 5 17 1 of low coniferous composition (Coleman et al. 2002). Also, fragmented landscapes, including forest edges and human the red-tailed hawk has been observed to nest specifically in developed landscapes (Rullman and Marzluff 2014). This well-covered and mature stands, however, this may be due to attraction towards urbanized fragmented landscapes has been predation threats in other land-cover areas rather than being suggested to be due to fragmented forests having greater nest- due to preferential habitats (Coleman et al. 2002). Former ing choices and forest openings than contiguous forests, and nesting sites also influence raptor habitat, for some raptors greater prey items supplemented by urbanization (Smith et al. will use the nests of separate species. The barred owl was 1999). Similarly, sharp-shinned hawks have been reported to observed by Dykstra et al. (2012) to frequently nest in recently nest within close proximity to forest openings associated with used nests of red-shouldered hawks (Buteo lineatus) within human activity within and surrounding the city of Montreal suburban areas (Dykstra et al. 2012). Time may also be an (Coleman et al. 2002). influencing factor, for the successful nesting sites of Cooper’s hawks was also observed to have rates of reoccupy of periods 2.6 Timescales of over 2 generations (Stout et al. 2007). Additionally, hawks have been suggested to behave with greater efficiency in new The age of neighbourhoods within certain landscapes may also nesting areas, with peak improvements occurring within the influence nesting. For example, old suburban neighbourhoods first 1-2 years (Mannan and Boal 2000). (> 75 years) with dense populations have been observed to include old trees that are likely to include cavities of sufficient size for nesting of species such as the barred owl (Dykstra 2.5 Fragmentation et al. 2012). Also, old neighbourhoods in Chicago, Illinois, Birds living within urban environments have been observed have been observed to have high degrees of undeveloped land- to favour fragmented habitats. Great horned owls (Bubo vir- cover (Loss et al. 2009) which may provide specialist habitat. ginianus) nesting in Connecticut, northern New Jersey, and However, population shifts have also been observed in aging southeastern New York were observed to select complex frag- neighbourhoods, including bird species richness decreasing mented habitats rather than communities in rural habitats with neighbourhood age, along with community composition (Smith et al. 1999). Great horned owls were even attracted changes from originally native and migratory birds to exotic to rural fragmented land-covers due to human developments and non-migratory birds (Loss et al. 2009). Thus older neigh- (Smith et al. 1999). Some raptors are known to excel within bourhoods in Peterborough may support greater diversities of Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 6/12

Figure 1. The richness of raptors within a gradient of urban and natural land-cover types within western, Washington, United states. The gray boxes represent species presence. The species are listed from highest site frequency. (Fig. 2. as cited in Rullman and Marzluf 2014, p 7) owl and specialist species, however, species habitation may in urban centres (Chace and Walsh 2006). Similarly, urban also depend on the size of the neighbourhood. Florida burrowing owls (Athene cunicularia floridana) have been observed with significantly different diets from rural 2.7 Human-Built Structures Florida burrowing owls, including with high insect diets and Human-built structures also effect raptor populations. Gen- more variable prey items (Mrykalo et al. 2009). However, the erally, developed fences, hedges and vegetative edges have study only recorded from one site in both urban and rural ar- been suggested to improve the hunting ability of raptors for eas, so this information may not be due to habitat differences prey items (Rullman and Marzluf 2014). For management (Mrykalo et al. 2009). Examples of raptors which consume purposes, these strategies may be implemented in cases where small prey are the burrowing owl and screech owl (Megas- local raptors are detrimentally limited by prey. On a smaller cops). The ferruginous hawk (Buteo regalis) and rough-legged scale, it has been suggested raptor species have greater repro- hawk (Buteo lagopus) are examples of raptors that consume ductive rates within human-made artificial nests than natural larger prey (Chace and Walsh 2006). Therefore, information nests (Chace and Walsh 2006). on rodent size and species found within Peterborough may be useful to further the understanding of the potential of each 2.8 Migratory Sites bird to adapt to developed landscapes. The City of Toronto released a “Literature Review and Data Assessment” of migratory birds in 2009, that likely has impli- 2.11 Rodent Abundance cations for migratory birds in Peterborough. In a broad sense, Hindmarch and Elliot (2015) observed rat prevalence as pos- birds may use nesting areas that have been routinely used itively related to urban-land area at barred owl nesting sites for generations, as suggested by this review (Konze 2009). within southwestern British Columbia. Barred owl rat preda- Additionally, many temperate and neotropical birds migrate tion was so great within urban environments that rats were past Toronto on their migration routes. The proximity of Pe- rated as the most consumed prey item (Hindmarch and El- terborough to Toronto may indicate that Peterborough is also liot 2015). However, the consumption of rodents in urban within the migratory range of these species. Toronto was also areas can put raptors at an increased risk of rodenticide ex- suggested to be a nesting stop for migratory birds that cross posure (see Literature Review: Urban Hazards: Disease and Lake Ontario; similarly Peterborough may be a reliable stop Poisoning) (Hindmarch and Elliot 2015). Raptor size can for birds traveling along the Otonabee River (Konze 2009). also limit preying ability within in certain developed areas. Scavenging raptors in the Rio Negro and Neuquen´ provinces 2.9 Prey/Diet of Argentina are known to use roads for scavenging, while 2.10 Prey Abundance the large hunting raptors do not appear to use the roads. This The ability of a raptor to find prey is of great importance. is suggested to be due to the relatively slow takeoff of large Chace and Walsh (2006) state that urban areas can positively raptors, which can increase the threat of roadside collisions influence the abundance of raptor prey, which then positively and hunting along roads (Lambertucci et al. 2009). In addi- influences raptor abundance (Chace and Walsh 2006). Red- tion to this abundance of prey, urban centers typically have an tailed and Swainson’s hawks (Buteo swainsoni) are examples abundance of anthropogenic waste and supplementary feeding of hawks that likely consume these high abundances of urban stations which habituated animals can use as food resources prey (Chace and Walsh 2006). Additionally, small prey are (Adams et al. 2006). Food resources in urban centers are specifically abundant in urban centers, and thus the raptors often distributed in concentrated locations, which results in that consume small prey are not likely to be limited by diet the distribution of animals concentrating in these areas. This Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 7/12 clumped distribution pattern is similar to natural environments 2007). This may be a major urban predation threat because of (Adams et al. 2006). the commonly high populations of raccoons.

2.12 Indications of High Prey Abundance 3. Urban Hazards In southeastern Arizona, Estes and Mannan (2003) observed 3.1 Collisions the prey delivery rate of Cooper’s hawks to urban nests to be While urban centers seem to be beneficial in terms of prey about twice as much as in rural nests. A high rate of prey and habitat, they also affect mortality rates and can be haz- delivery to nests may indicate an abundance of prey within the ardous to resident raptor species. Potential hazards include respective habitat (Estes and Mannan 2003). An abundance vehicular and window collisions, built structures, artificial of readily available prey items can also be indicated by hawks lighting, roads and diseases. In a comprehensive review of that continually deliver prey items to nestlings, while able to 86 articles, Hager (2009) discusses urban hazards to raptor vary their hunting effort to meet nestling diet requirements populations. The main hazards were window and vehicle colli- (Estes and Mannan 2003). When there is a high abundance of sions and electrocutions; the collisions and electrocutions are prey in a given site, hawk hunting locations will likely become substantial hazards in both urban and natural environments. dependent on the location of their nests (Mannan and Boal Lighting from human developments can also cause mortal- 2000). ities. In 1996, the Fatal Light Awareness Program (FLAP) stated that Toronto had an annual mortality rate of 732 deaths 2.13 Predation on raptors due to artificial lighting (Ogden 1996). Light towers are also Raptor species that prey upon other raptors will likely affect a major cause of bird mortalities, 6.8 million tower-related species abundance and distribution. For example, the Cooper’s bird kills annually are estimated within United States and hawk is a known predator of the sharp-shinned hawk (Cole- Canada (Longcore et al. 2012). Thus lit antenna towers and man et al. 2002). Thus, urban areas with a high abundance other structures within Peterborough may cause mortalities. of raptor-predating species such as the Cooper’s hawk may In addition, rural land changes such as land-expansion can put cause reductions in the numbers of the preyed-upon raptors pressure on wildlife by limiting or removing habitats (Neave such as the sharp-shinned hawk (Coleman et al. 2002). This is et al. 2000). Developing forested land-cover within urban cen- not specifically relevant to the available sighting data for these ters would have the same negative effects on nesting raptors; two species within Peterborough, as the sharp-shinned hawk positive changes would likely occur with park restoration, or has higher sighting counts than the Cooper’s hawk from 2 out forest planting. of 3 of the sighting sources within Table 2 and higher sighting counts within every city in Table 3. Nest depredation is also 3.2 Roads relevant, for raptors within urban centers have been observed Raptors use roads and their surrounding structures for for- as more likely to prey on avian nests in rural areas than urban aging road kills, hovering and hunting prey (Hager 2009). areas (Rodewald and Kerns 2011). Similarly, Rodewald et Roads can also disturb bird populations through noise levels, al. (2011) observed separations of interrelated connections visual disturbance and prey concealment (Bautista et al. 2004). between breeding birds and nest predators living in urban However, in terms of vehicular collisions, Hager (2009) found areas. This may be due to the abundance of additional prey that moralities were not significantly different between urban and food resources for predators within urban environments. and natural environments. Road disturbance to raptor species’ This separation may increase successful nesting potential in may occur on weekly cycles depending on traffic variations, urban environments, for nestlings likely have a higher survival because scavenging raptor road-occurrence has been observed potential with a lack of predation. to decrease during weekends with high traffic loads (Bautista Supplementary food from bird feeders in particular can et al. 2004). This may have implications for Peterborough attract avian wildlife to specific locations. Some raptors such during summer weekends, when tourism is likely highest. as the Cooper’s and sharp-shinned hawk may prey upon the birds that are attracted to feeders, and thus are also attracted 3.3 Feeding Stations to these feeders (Allaboutbirds.org 2016f). However, this is Bird feeding stations can cause issues with urban-living bird not always the case: Roth et al. (2008) found no significant species. Although these stations provide a concentrated and difference in predation from Cooper’s hawks at bird feeders. consistent source of food, the feeders can directly and indi- Feeders can also be detrimental to the birds that use them rectly cause mortalities. Feeders located near windows can and raptors (see Literature Review: Urban Hazards: Feeding attract birds and can cause window collision mortalities (Klem Stations). 1990). Raptors are also susceptible to window collisions for Nests within urban areas may also encounter predation they may prey on birds located at these feeders (Boal and from other urban adapted animals such as raccoons. Raccoons Mannan 1999). Hunters have also been found to use feeding may be an undocumented predator to raptor species and their stations to attract raptor species; this may occur at rates higher eggs, as they use similar habitats to Cooper’s hawk nesting than currently recorded if the hunting is illegal (Boal and sites and prey upon similarly sized eggs and birds (Stout et al. Mannan 1999). Also, feeders have the potential of exposing Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 8/12 birds to Trichomoniasis (Davidson and Nettles 1988 as cited low human tolerance and/or specialist requirements, a suffi- in Boal Mannan 1999) which may transfer to raptors that feed cient density of undeveloped patches can be estimated with on these birds (see Literature Review: Urban Hazards: Dis- an understanding of each species’ average flight and alert ease and Poisoning below) (Friend and Franson 1999; Boal et distances (Campbell 2009). Additionally, fenced corridors al. 1998). between undeveloped patches may increase the potential of colonization of species with low human tolerances (Camp- 3.4 Disease and Poisoning bell 2009). Shrub patch size and proximity to roads are also Urban adapted raptors may be required to cope with vari- important land features to consider when planning because ous diseases, including Trichomoniasis. Trichomonas galli- of their relevant consequences of human activity (Campbell nae (Trichomoniasis) is an endemic parasite of which doves 2009). Loss et al. (2009) suggest that natural land-cover (columbidae) are the foremost host (Stabler 1954 as cited in patches can increase avian richness within populations over 2 Estes and Mannan 2003; Lawson et al. 2011). This can be km away on average, and within urban landscapes composed passed on to raptor species that prey upon small birds such of less than 20% natural land-cover patches (including park as doves. Ultimately, the spread of Trichomoniasis depends and undeveloped land) (Loss et al. 2009). There are 102 on the degree to which the hosts are present in a raptor’s parks with varying sizes and levels of forest cover distributed diet (Boal and Mannan 1999). Another danger is the infu- throughout Peterborough, which are generally within 1-3 km sion of seeds with organophosphates as a poison control of of each other, and thus may increase suitable raptor habitat feral pigeons; this similarly puts raptors that consume these (Figure 4). pigeons at risk of organophosphate poisoning (Boal and Man- nan 1999). In addition, as noted above (Literature Review: 4.2 Species size Prey/Diet: Rodent Abundance), there can be high abundances Urban forests and parks can be managed to provide habitat of small prey such as rats within urban environments (Chase for larger birds that are not normally associated with urban and Walsh 2006; Hindmarch and Elliot 2015). This abundance areas. These birds will likely require large areas of contiguous would increase the risk of raptors becoming exposed to ro- forests (Campbell 2009). Large raptors sighted in Peterbor- denticides (such as anticoagulant rodenticides [AR]) through ough include the great horned owl, the great gray owl (Strix secondary exposure; rats were the main pathway for AR to nebulosa) and the red-tailed hawk. Larger birds may require barred owls exposure from a study in southwestern British isolation within these areas, this can be achieved with high Columbia (Hindmarch and Elliot 2015). density forests and by fencing off certain areas (Campbell 2009). 3.5 Human Communities 4.3 Diseases Raptors within urban and suburban environments can be no- In managing for bird feed related diseases such as Trichomo- ticed and appreciated by neighborhood communities (Boal niasis, Mannan and Boal (1999) recommend the regular clean- and Mannan 1999). However, there have been instances of ing of feeders, “dove-proof feeders”, and the general avoid- individuals being intentionally hit by Cooper’s hawks in Tuc- ance of attracting doves to the feeders (p 82). There are son, Arizona, due to nest protection and defensive behaviours available treatments for Trichomoniasis, however, they usu- (Boal and Mannan 1999). Aside from concerns of injuries, ally result in bacterial infections or mortalities even when the potential threats of these nests within human communities successful, and thus euthanizing infected individuals has been can cause humans to mistrust raptor nests (Boal and Mannan recommended (Boal and Mannan 1999). 1999). Thus, educating the communities with an ecological A potential alternative of rodenticide use is to use rap- understanding of this behaviour should positively influence tors as a natural pest control (Hungeryowl.org 2016). This is local opinions (Boal and Mannan 1999). also a potential alternative to the use of organophosphate poi- sons. For example, owls may be encouraged to act as natural 4. Management Implications rodent pest management by building owl boxes for nesting (Hungryowl.org 2016). Community groups and organizations 4.1 Land-cover within Peterborough could advertise and create incentives to To effectively manage for each species, the biology of the implement these within Peterborough. However, in order for species, its population and limiting requirements should be this to be effective, poison use would first need to be reduced understood. In terms of land-cover, it is recommended by to prevent exposure, and raptor habitats may require proper Campbell (2009) to plant a variety of forest densities for management of land-planning. human tolerant and non-tolerant bird species. Similarly, Cole- man et al. (2002) recommends that forest stands within urban 4.4 Planning centers should be considered raptor habitats and thus be con- Management should focus on specific specialist species, for served. Additionally, fragmented forest patches within an generalist species are less likely to require management due to urban landscape benefit generalist raptors, and thus should their ability to adapt to a greater range of habitats. Within gen- be conserved (Rullman and Marzluf 2014). For species with eralists and specialists, it seems that individual species have Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 9/12

Figure 2. Park locations within the City of Peterborough, Ontario, Canada. (For an enlarged map, see Peterborough.ca 2016) Urban Raptors: Owl and Hawk Adaptation to Urban Centers — 10/12 their own requirements for habitat and prey. Therefore, ur- species population rather than the traits of a species in general ban managers focused on raptors should manage for specialist (Dykstra et al. 2012). species that are affected by the most limiting factors. Addition- This report demonstrates general responses of raptors to ally, planners may focus on increasing the available habitat urban areas, and it would be useful for other studies to include for endangered species such as the barn owl, however, this broader implications on urban responses to seek out more would expose them to potentially threatening urban hazards generalized trends. Local results are useful in respect to the (see Literature Review: Urban Hazards) (Ontario.ca 2016). local management of species but may limit the usability of Managing for specialist species may create an umbrella of pro- their results on a broader scale. A generalized understanding tection, by providing a greater amount of available resources of raptor response to urban areas is also useful, for it provides for less limited specialist species and generalist species. In resources to regions distant from the original study locations. other words, managing for specialists would likely improve The available information on raptor adaptation should be used resource availability for low abundance raptor populations. by wildlife managers, researchers and policy makers to im- However, there is insufficient sighting information for Peter- prove and continue our shared use of urban centers with these borough to determine which species are of high or low urban species. abundance. Therefore a systematic evaluation of urban avian wildlife abundance and distribution within the city would be useful for this purpose. Acknowledgments This paper was originally for David Beresford’s Environmen- 5. Conclusion tal Seminar Course (ERSC-4730). The ability of raptor species to adapt to urban environments seems to be dependent on resource availability, commonly in References terms of habitat and diet requirements and their generalist or 12.statcan.gc.ca. 2016a. Peterborough Census Profile. specialist requirements with respect to these resources. Gen- Available from http://www12.statcan.gc.ca/ eralist species are commonly better able to adapt to urban census-recensement/2011/dp-pd/prof/det environments, while some specialist species can adapt with ails/page.cfm?Lang=E\&Geo1=CSD\&Code1= the availability of specific habitat, and prey. Urban center 3515014\&Geo2=CD\&Code2=3515\&Data=Coun resources can differ from natural areas through factors such t\&SearchText=Peterborough\&SearchType as supplementary feeding and prey abundance (Smith et al. =Begins\&SearchPR=01\&B1=All\&Custom=\& 1999; Adams et al. 2006; Hindmarch and Elliot 2015), built- TABID=1 [accessed 11 January 2016]. structure influences (Hager 2009; Rullman and Marzluff 2014; Longcore et al. 2012), decreased contiguous forest cover, Adams, C. E., Lindsey, K. J., Ash, A. J. 2006. Urban Wildlife natural predators (Campbell 2009; Adams et al. 1006) and Management, Taylor & Francis Group. Boca Raton, Florida. increased land-cover heterogeneity (Campel 2009). 84-85. Allaboutbirds.org 2016d. Birding Reference Guide. The Cor- The Peterborough sighting counts (Table 2 and 3) are lim- nell Lab of Ornithology. Available from https://ww ited in their ability to accurately demonstrate distribution or w.allaboutbirds.org/guide/ [accessed January abundance; however, they are important tools for understand- 11, 2016] ing the presence of specific species. The broad-winged and red-tailed hawks had the highest counts of all recorded species, Bautista, l., Garc´ıa, J., Calmaestra, R., Palac´ın, C., Mart´ın, C., while the great gray and great horned owls had slightly higher Morales, M., et al. 2004. Effect of weekend road traffic counts than other owls. Additionally, there was only one on the use of space by raptors. Conservation Biology 18: sighting of the endangered barn owl (Ontario.ca 2016). It 726-732. doi: 10.1111/j.1523-1739.2004.00499.x. would be useful to have an intensive record of bird species Bezener, A. 2000. Birds of Ontario. Lone Pine Publishing. abundance and distribution in addition to these sightings for Edmonton. 97. Peterborough and other urban centers. Bird, D., Varland, D., and Negro, J. 1996. Raptors in human With respect to the reviewed literature, many studies have landscapes. Academic Press, London. Preface, xiii. been done in the United States on raptors in urban centers, Birdsontario.org. 2016. Atlas of the Breeding Birds of On- however, few have been conducting regarding Canadian urban tario. Region 16. Peterborough, list of species. Avail- centers. Also, many of the studies focus on how specific able from http://www.birdsontario.org/atl species responded to urban habitat/prey availability. This is as/datasummaries.jsp\#results [accessed Jan- generally useful information, however, the degree to which uary 11, 2016] these species will show similar trends between separate popu- Boal, C., and Mannan, R. 1999. Comparative breeding ecol- lations and other urban centers is uncertain. 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