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1 June 2013 A Journey of Raptor Research: Commemorating the Scientific Contributions of Gary R. Bortolotti
Russell D. Dawson
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This special issue of the Journal of Raptor Research is dedicated to the memory of Gary R. Bortolotti. Gary's passion and excitement for avian research, and in particular for raptors, was extremely infectious, and he instilled this excitement in all of us who were fortunate enough to have had the privilege of working with him over the course of his career. Sadly, Gary's career was cut short with his untimely passing on 3 July 2011 at the age of 56 years. Those left behind felt a deep sense of loss, not only because he was a valued colleague, but also because we had lost a great friend. Soon after his passing, a proposal was made that an appropriate way to honor Gary's memory would be to publish a selection of papers in a special issue of the Journal of Raptor Research, and I am privileged to write the introduction to this issue. A number of tributes and memorials to Gary have already been published both in this issue (Arroyo et al. 2013, Houston 2013) and elsewhere (Dawson 2011, Blas et al. 2011, Gerrard 2011, Houston and Gerrard 2011); readers wishing more details on Gary's life are referred to these. In the text that follows, I therefore provide an overview of the diversity of research interests that Gary pursued over his career, and integrate these with a brief synopsis of the topics that are included in this issue.

Eagles and Besnard Lake

The research interests that occupied the career of Gary Bortolotti were many and diverse. Although he received his B.Sc. in Forestry from the University of Toronto, during the course of his undergraduate degree it became apparent that forestry was not his true calling. Gary contacted Jon M. Gerrard, a professor of hematology at the University of Manitoba with a keen interest in raptors who, along with Douglas W.A. Whitfield, had been studying the Bald Eagles (Haliaeetus leucocephalus) that nested around Besnard Lake, in Saskatchewan's boreal forest. Jon was able to get Gary out to Saskatchewan and out onto the lake for a summer to conduct surveys of the eagles. This first trip to Besnard Lake was formative, and Gary continued to study the eagles at Besnard for his Ph.D., completed in 1984 under the supervision of Jon C. Barlow of the Royal Ontario Museum. Unquestionably, Besnard Lake would play a central role not only in Gary's professional career, but in his personal life as well.

The initial motivation for Gerrard and Whitfield to first go to Besnard in the late 1960s was to conduct a population census of Bald Eagles, and over the course of many decades of surveys, the population dynamics of eagles at Besnard Lake have been extremely well documented (e.g., Gerrard et al. 1990), as have their general patterns in reproductive biology over a similar time frame (Gerrard et al. 1992). Indeed, the extensive time spent on the water working on eagles also has allowed for population surveys of other birds using the aquatic environments of Besnard Lake (Gerrard et al. 1993, Bortolotti et al. 1996b, Gerrard et al. 2006). Gary and Jon's general interest in the birds of this area of Saskatchewan, as well as Gary's later work on American Kestrels (Falco sparverius) in the area surrounding the lake, culminated in a 27-yr-long inventory of the birds of Besnard Lake and the surrounding boreal forest (Gerrard et al. 1996). In the present issue of Journal of Raptor Research, Mougeot et al. (2013) continue to examine trends in both population size and productivity of the Bald Eagles of Besnard Lake. Their study is particularly noteworthy for its duration, which encompasses over 40 yr. Such investigations are rare, but extremely important for the insights that they reveal; Mougeot et al. (2013) are able to demonstrate that many of the reproductive variables of eagles show density dependence, and that there also is density dependence in population growth rate, suggesting that this population of Bald Eagles is being regulated.

During the course of Gary's Ph.D. research, he was able to develop some simple and accurate methodologies for determining the sex of both mature and adult Bald Eagles based on their morphology (Bortolotti 1984b, 1984c). Gary also developed similar methods for determining sex of Golden Eagles (Aquila chrysaetos; Bortolotti 1984a), and in this issue Harmata and Montopoli (2013) present results of their study of morphological variation in Golden Eagles, where they are able to correctly classify the sex of birds with 100% accuracy. The determination of the sex of nestling Bald Eagles was an important step in Gary's innovative research on facultative sex ratio manipulation. Like most raptors, Bald Eagles show reverse sexual size dimorphism, with females larger than males. Gary showed that male-first, female-second broods were rare in Bald Eagles because they lead to greater sibling conflict (Bortolotti 1986). Sex ratios, sibling competition and aggression, and sex biases in the order of hatching of eagles continued to be a fruitful area of research for the next decade and beyond (e.g., Bortolotti 1989, Dzus et al. 1996, Wiebe and Bortolotti 2000). In this issue, Woolaver et al. (2013) examine sex ratios in Ridgway's Hawks (Buteo ridgwayi) and show that the remaining females in this endangered species show a consistent bias for producing female-biased broods, which may be a consequence of abundant food resources for these birds, or alternatively a consequence of inbreeding.

The Kestrel Years

Although the focal species of Gary's research changed from Bald Eagles to American Kestrels when he became a faculty member in the Department of Biology at the University of Saskatchewan in 1987, the physical location of his studies remained the area around Besnard Lake. An extensive network of nest boxes was established along roads and logging trails within an approximately 80-km radius of Besnard, and the convenience of using a nest-box population of kestrels for research was immediately apparent. In fact, research on kestrels at the Besnard study site has continued more or less continuously up until the present (e.g., Smallwood et al. 2009, Greenwood and Dawson 2011), primarily because of the logistics associated with using nest boxes. In this issue, Liébana et al. (2013) report on occupancy of nest boxes by raptors in central Argentina, while Rodríguez et al. (2013) describe the establishment of a breeding colony of Lesser Kestrels (Falco naumanni) within an urban environment.

With American Kestrels, Gary's work focused on an array of issues, including more studies on facultative sex ratio manipulation, as well as the causes and consequences of hatching asynchrony, parasitism, and parental investment decisions (e.g., Wiebe and Bortolotti 1992, 1994a, 1994b, Dawson and Bortolotti 2001, 2002). One key question that Gary was interested in examining was how American Kestrels selected mates, and while he was not able to perform experimental studies, he was able to show that they paired assortatively with respect to both body condition and feather quality (Bortolotti and Iko 1992, Bortolotti et al. 2002). In this issue, Arroyo et al. (2013) examine the sexual functions of sky-dancing displays in Montagu's Harrier (Circus pygargus), and show that males have more intensive displays and that such displays are costly for the individuals performing them, suggesting that they are traits that are honest advertisements of individual quality.

Indeed, during many of his studies, one of the key characters that Gary attempted to quantify in kestrels was some component of “individual quality.” And while defining exactly what individual quality actually might be is difficult, he nonetheless tested the utility of various aspects of blood chemistry (e.g., Dawson and Bortolotti 1997) and feather quality (fault bars; Bortolotti et al. 2002) as surrogates for quality. Kestrels also have bare skin at the base of the bill and anterior to the eyes, the cere and lores, respectively, which ranges from dull yellow to bright orange, and he began to quantify variation in coloration among individual birds. Such coloration in animals often is the result of the deposition of carotenoid pigments, which animals cannot synthesize and therefore must be obtained from the diet. Brightly colored birds may therefore be advertising their quality because it shows superior foraging ability. Carotenoids also have many biological functions, including roles in the immune system and as antioxidants for detoxifying free radicals, so the ability to deposit these pigments in ornaments as opposed to utilizing them for physiological processes may also indicate an individual's quality.

In 1995, Gary made a trip to David Bird's Avian Science and Conservation Centre (ASCC) at MacDonald College of McGill University, where David kept a captive colony of American Kestrels. The goal of this trip was to gain further insight into the physiological underpinnings of the expression of color by kestrels, and together with Spanish colleagues, Gary provided evidence that these traits in kestrels were condition dependent and sexually selected, and furthermore, by examining seasonal patterns of coloration and circulating carotenoids, that kestrels were physiologically regulating their expression of color (Bortolotti et al. 1996a, Negro et al. 1998). Although much work has focused on carotenoid-dependent color within the context of sexual selection, in this issue Blas et al. (2013) examine skin color in the highly social Black Kite (Milvus migrans), and test its role as a signal of status in social situations beyond mate choice and sexual selection. Their results also suggest that kites are physiologically regulating the expression of carotenoid traits, and furthermore that this regulation differs not only between the sexes, but also between breeders and floaters within the population.

An Evolving Research Agenda

The original work that Gary conducted at the ASCC on carotenoids and coloration of kestrels with Spanish colleagues resulted in collaborations that were enduring, and Gary would eventually develop many friendships and close working relationships with other Spanish researchers. At the same time, the work on carotenoids and coloration would ultimately lead to a major shift in the direction of his research program. Ecologists were becoming increasingly interested in using various methods in an attempt to quantify an individual's ability to respond to challenges to their immune system, and Gary was involved in studies that were among the first to relate immune responses of nestlings to attributes of their parents (Tella et al. 2000a), as well as to examine the heritability of immunocompetence (Tella et al. 2000b). As some of his research became more physiologically oriented, Gary and colleagues developed a number of projects examining issues related to toxicology, such as the exposure of Bald Eagles to lead poisoning in prairie Canada (e.g., Miller et al. 2001), as well as a multifaceted study looking at an array of effects resulting from exposure of American Kestrels to polychlorinated biphenyls (e.g., Fernie et al. 2001, Bortolotti et al. 2003). Not only was this new avenue of research driven by an interest in using physiological tools to answer behavioral and ecological questions, but also I believe from Gary's desire that his research make a contribution toward the conservation of species. In this issue, Speziale and Lamertucci (2013) examine the published literature on how introduced nonnative species influence raptors, and while there is clearly a paucity of information available, the majority of evidence suggests the effects are detrimental, owing both to reductions in the prey base of birds, or through poisoning associated with the introduced species.

Perhaps related to his long-term interest in individual quality, Gary developed a keen interest in measuring stress levels in birds (e.g., Blas et al. 2005), which eventually led to the development of a novel noninvasive technique to quantify avian endocrine status through feather composition. This involved the extraction of the primary stress hormone of birds, corticosterone, from feathers (Bortolotti et al. 2008, 2009a). While the groundbreaking technique of using corticosterone levels in feathers as a means to monitor stress in wild bird populations opened up new avenues of research not only for Gary but for all avian ecologists, it also has allowed the reexamination of many previous questions. For example, it was now possible to examine the role that stress played in the expression of secondary sex traits and more clearly understand that the ability to express ornaments was ultimately a result of the cumulative physiological response to challenges individuals faced from their environment (Bortolotti et al. 2009b). Similarly, while some of his previous work on kestrels examined the role that parasites might play in mediating color expression (Dawson and Bortolotti 2006), it was now feasible to examine such relationships in much greater breadth than was previously possible (Mougeot et al. 2010). Coloration of nestling birds, and in particular raptors, has been largely ignored in previous studies, but in this issue, Martínez-Padilla et al. (2013) examine relationships between feather corticosterone and carotenoid-dependent skin coloration in nestling Common Buzzards (Buteo buteo). They show that the degree of coloration is negatively related to corticosterone levels, but only among female nestlings, again suggesting that regulation of coloration and carotenoids is carried out differently by each sex (see also Blas et al. 2013).

Corticosterone level in feathers of nestlings has added a new dimension to assessing the impacts of pollution on birds (Harms et al. 2010) and has also revealed sex-specific investment strategies by parents (Fairhurst et al. 2012). In this issue, Yosef et al. (2013) examine how resource availability and sibling competition influence stress responses of Upland Buzzards (Buteo hemilasius), and show that although nutritional condition appears to have little influence on responses, junior siblings have higher levels of feather corticosterone than their senior siblings. Because these differences became more pronounced as the age difference between siblings increased, this study provides compelling evidence for the importance of sibling conflict in mediating levels of stress within nestling raptors.

Coming Full Circle

In recognition of his research accomplishments, the Department of Biology at the University of Saskatchewan named Gary the first Stuart and Mary Houston Professor of Ornithology in 2002 (Houston 2013). In addition to the honor of holding this professorship, it allowed the pursuit of research opportunities that otherwise might not have been possible. For example, Gary was able to assess whether the white plumage of Snowy Owls (Bubo scandiacus) could act as a social signal, and further, how the signaling potential of this trait could be modified with behavioral adjustments such as body posture and orientation (Bortolotti et al. 2011). In this issue, Bettega et al. (2013) similarly explore the signaling role of white plumage patches in Eurasian Eagle-Owls (Bubo bubo) and, in addition to showing age and sexual dimorphism, are able to demonstrate condition dependence of reflectance patterns. The Houston Professorship also facilitated work on Turkey Vultures (Cathartes aura), a species that has increased in number and expanded their breeding range within Saskatchewan over the past 30 yr (Houston et al. 2007). Herein, Rollack et al. (2013) report on a number of aspects of breeding Turkey Vultures in Saskatchewan and, through the use of cameras mounted within the abandoned buildings that are used for nesting sites, are able to provide new information on natal dispersal distances as well as age at first breeding. Using satellite transmitters, the Saskatchewan vultures also were tracked to their wintering ranges in Venezuela, which were considerably larger than has been previously reported (Hedlin et al. 2013).

The relationships and linkages between Stuart Houston and Gary Bortolotti have roots that extend much longer and deeper than the Houston Professorship. Houston's influence on the ornithological community is substantial and well known, and Stuart has a long history of providing mentorship to aspiring amateur biologists, especially raptor enthusiasts. Among the many mentees of Stuart's was Jon Gerrard, who in turn provided mentorship to Gary and so influenced the direction that Gary's professional life was to take. It is therefore appropriate that this special issue of the Journal of Raptor Research close with some of Stuart's personal reflections on Gary (Houston 2013). In a sense, we have come full circle.

Closing Remarks

This issue of the Journal of Raptor Research is dedicated to the memory of Gary Roy Anthony Bortolotti—professor, biologist, photographer, mentor, husband, father, and friend. His passion, enthusiasm, colorful language, warmth, humor, and friendship will be profoundly missed, but never forgotten.{ label needed for fig[@id='i0892-1016-47-2-89-f01'] }

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Gary Bortolotti at Besnard Lake, Saskatchewan, Canada, in 2004. Photo courtesy of Heather Trueman.



I am grateful for the information provided by Heather Trueman, Jon Gerrard, Linda and Michael Hutcheon, and Vipen Sawhney. I thank Karen Wiebe for helpful discussions, and Erin O'Brien and Cheryl Dykstra for comments on a previous draft. Most importantly, I am deeply indebted to Gary Bortolotti for providing me with a stimulating environment both as an undergraduate and graduate student, for the freedom to pursue the questions I was interested in, for the privilege of being able to conduct fieldwork together, and for being such a wonderful friend and colleague to me.

Literature Cited


B Arroyo F Mougeot and V Bretagnolle 2013. Characteristics and sexual functions of sky-dancing displays in a semi-colonial raptor, the Montagu's Harrier (Circus pygargus). Journal of Raptor Research 47:185–196. Google Scholar


B Arroyo J.J Negro and J Blas 2013. Personal reflections on Gary Bortolotti's links with Spain. Journal of Raptor Research 47:219–220. Google Scholar


C Bettega L Campioni M Del Mar Delgado R LourenÇo and V Penteriani 2013. Brightness features of visual signaling traits in young and adult Eurasian Eagle-Owls. Journal of Raptor Research 47:197–207. Google Scholar


J Blas R Baos G.R Bortolotti T Marchant and F Hiraldo 2005. A multi-tier approach to identifying environmental stress in altricial nestling birds. Functional Ecology 19:315–322. Google Scholar


J Blas S Cabezas J Figuerola L López A Tanferna F Hiraldo F Sergio and J.J Negro 2013. Carotenoids and skin coloration in a social raptor. Journal of Raptor Research 47:174–184. Google Scholar


J Blas R.D Dawson J.J Negro J.L Tella and K.L Wiebe 2011. In memorium: Gary R.A. Bortolotti, 1954–2011. Newsletter of the Animal Behaviour Society 56(4):8–9. Google Scholar


G.R Bortolotti 1984a. Age and sex size variation in Golden Eagles. Journal of Field Ornithology 55:54–66. Google Scholar


G.R Bortolotti 1984b. Criteria for determining age and sex of nestling Bald Eagles. Journal of Field Ornithology 55:467–481. Google Scholar


G.R Bortolotti 1984c. Sexual size dimorphism and age-related size variation in Bald Eagles. Journal of Wildlife Management 48:72–81. Google Scholar


G.R Bortolotti 1986. Influence of sibling competition on nestling sex-ratios of sexually dimorphic birds. American Naturalist 127:495–507. Google Scholar


G.R Bortolotti 1989. Sex-ratios of fledgling Golden Eagles. Auk 106:520–521. Google Scholar


G.R Bortolotti R.D Dawson and G.L Murza 2002. Stress during feather development predicts fitness potential. Journal of Animal Ecology 71:333–342. Google Scholar


G.R Bortolotti K.J Fernie and J.E Smits 2003. Carotenoid concentration and coloration of American Kestrels (Falco sparverius) disrupted by experimental exposure to PCBs. Functional Ecology 17:651–657. Google Scholar


G.R Bortolotti and W.M Iko 1992. Nonrandom pairing in American Kestrels: mate choice versus intrasexual competition. Animal Behaviour 44:811–821. Google Scholar


G.R Bortolotti T Marchant J Blas and S Cabezas 2009a. Tracking stress: localisation, deposition and stability of corticosterone in feathers. Journal of Experimental Biology 212:1477–1482. Google Scholar


G.R Bortolotti T Marchant J Blas and T German 2008. Corticosterone in feathers is a long-term, integrated measure of avian stress physiology. Functional Ecology 22:494–500. Google Scholar


G.R Bortolotti F Mougeot J Martinez-Padilla L.M.I Webster and S.B Piertney 2009b. Physiological stress mediates the honesty of social signals. PLoS ONE 4:e4983. Google Scholar


G.R Bortolotti J.J Negro J.L Tella T.A Marchant and D.M Bird 1996a. Sexual dichromatism in birds independent of diet, parasites and androgens. Proceedings of the Royal Society of London B 263:1171–1176. Google Scholar


G.R Bortolotti M.J Stoffel and I Galvan 2011. Wintering Snowy Owls Bubo scandiacus integrate plumage colour, behaviour and their environment to maximize efficacy of visual displays. Ibis 153:134–142. Google Scholar


G.R Bortolotti K.L Wiebe and J.M Gerrard 1996b. Diversity and population trends of the birds of Besnard Lake. Pages 33–44 in P Jonker [Ed.], The Churchill: a Canadian heritage river, proceedings of the Churchill Heritage River Conference. Univ. of Saskatchewan Extension Press, Saskatoon SK, Canada. Google Scholar


R.D Dawson 2011. Remembering Gary R.A. Bortolotti, 1954–2011. Picoides 24((3)):11–12. Google Scholar


R.D Dawson and G.R Bortolotti 1997. Are avian hematocrits indicative of condition? American Kestrels as a model. Journal of Wildlife Management 61:1297–1306. Google Scholar


R.D Dawson and G.R Bortolotti 2001. Sex-specific associations between reproductive output and hematozoan parasites of American Kestrels. Oecologia 126:193–200. Google Scholar


R.D Dawson and G.R Bortolotti 2002. Experimental evidence for food limitation and sex-specific strategies of American Kestrels (Falco sparverius) provisioning offspring. Behavioural Ecology and Sociobiology 52:43–52. Google Scholar


R.D Dawson and G.R Bortolotti 2006. Carotenoid-dependent coloration of male American Kestrels predicts ability to reduce parasitic infections. Naturwissenschaften 93:597–602. Google Scholar


E.H Dzus G.R Bortolotti and J.M Gerrard 1996. Does sex-biased hatching order in Bald Eagles vary with food resources? Ecoscience 3:252–258. Google Scholar


G.D Fairhurst J Navarro J Gonzalez-Solis T.A Marchant and G.R Bortolotti 2012. Feather corticosterone of a nestling seabird reveals consequences of sex-specific parental investment. Proceedings of the Royal Society of London B 279:177–184. Google Scholar


K.J Fernie J.E Smits G.R Bortolotti and D.M Bird 2001. Reproduction success of American Kestrels exposed to dietary polychlorinated biphenyls. Environmental Toxicology and Chemistry 20:776–781. Google Scholar


J Gerrard 2011. Tribute to Gary Bortolotti. Wingspan 20:18. Google Scholar


J.M Gerrard G.R Bortolotti E.H Dzus P.N Gerrard and D.W.A Whitfield 1990. Boat census of Bald Eagles during the breeding season. Wilson Bulletin 102:720–726. Google Scholar


J.M Gerrard G.R Bortolotti and K.L Wiebe 1996. Birds of the Besnard Lake area north-central Saskatchewan, 1968–1994. Nature Saskatchewan, Regina, Saskatchewan. Google Scholar


J.M Gerrard E Dzus G.R Bortolotti and P.N Gerrard 1993. Water-bird population-changes in 1976–1990 on Besnard Lake, Saskatchewan: increases in loons, gulls, and pelicans. Canadian Journal of Zoology 71:1681–1686. Google Scholar


J.M Gerrard P.N Gerrard P.N Gerrard G.R Bortolotti and E.H Dzus 1992. A 24-year study of Bald Eagles on Besnard Lake, Saskatchewan. Journal of Raptor Research 26:159–166. Google Scholar


J.M Gerrard P.N Gerrard E.H Dzus G.R Bortolotti and E Scragg 2006. Population changes in water-associated birds at Besnard Lake, Saskatchewan 1976–2005. Blue Jay 64:149–154. Google Scholar


J.L Greenwood and R.D Dawson 2011. Risk of nest predation influences primary reproductive investment in American Kestrels (Falco sparverius): an experimental test. Journal of Raptor Research 45:15–26. Google Scholar


A Harmata and G Montopoli 2013. Morphometric sex determination of North American Golden Eagles. Journal of Raptor Research 47:108–116. Google Scholar


N.J Harms G.D Fairhurst G.R Bortolotti and J.E.G Smits 2010. Variation in immune function, body condition, and feather corticosterone in nestling Tree Swallows (Tachycineta bicolor) on reclaimed wetlands in the Athabasca oil sands, Alberta, Canada. Environmental Pollution 158:841–848. Google Scholar


E.M Hedlin C.S Houston P.D McLoughlin M.J Bechard M.J Stoffel D.R Barber and K.L Bildstein 2013. Winter ranges of migratory Turkey Vultures in Venezuela. Journal of Raptor Research 47:145–152. Google Scholar


C.S Houston 2013. Personal reflections on Gary Bortolotti and synchronicity. Journal of Raptor Research 47:221–222. Google Scholar


C.S Houston and J.M Gerrard 2011. In memoriam: Gary Bortolotti, 1954–2011. Auk 128:798–799. Google Scholar


C.S Houston B Terry M Blom and M.J Stoffel 2007. Turkey Vulture nest success in abandoned houses in Saskatchewan. Wilson Journal of Ornithology 119:742–747. Google Scholar


M.S Liébana J.H Sarasola and M.Á Santillán 2013. Nest-box occupancy by neotropical raptors in a native forest of central Argentina. Journal of Raptor Research 47:208–213. Google Scholar


J MartÍnez-Padilla F Mougeot J.T GarcÍa B Arroyo and G.R Bortolotti 2013. Feather corticosterone levels and carotenoid-based coloration in Common Buzzard (Buteo buteo) nestlings. Journal of Raptor Research 47:161–173. Google Scholar


M.J.R Miller M.E Wayland and G.R Bortolotti 2001. Exposure of migrant Bald Eagles to lead in prairie Canada. Environmental Pollution 112:153–162. Google Scholar


F Mougeot J Gerrard E Dzus B Arroyo P.N Gerrard C Dzus and G.R Bortolotti 2013. Population trends and reproduction of Bald Eagles at Besnard Lake, Saskatchewan, Canada, 1968–2012. Journal of Raptor Research 47:96–107. Google Scholar


F Mougeot J Martinez-Padilla G.R Bortolotti L.M.I Webster and S.B Piertney 2010. Physiological stress links parasites to carotenoid-based colour signals. Journal of Evolutionary Biology 23:643–650. Google Scholar


J.J Negro G.R Bortolotti J.L Tella K.J Fernie and D.M Bird 1998. Regulation of integumentary colour and plasma carotenoids in American Kestrels consistent with sexual selection theory. Functional Ecology 12:307–312. Google Scholar


A RodrÍguez J.J Negro J Bustamante and J AntolÍn 2013. Establishing a Lesser Kestrel colony in an urban environment for research purposes. Journal of Raptor Research 47:214–218. Google Scholar


C.E Rollack K.L Wiebe M.J Stoffel and C.S Houston 2013. Turkey Vulture breeding behavior studied with trail cameras. Journal of Raptor Research 47:153–160. Google Scholar


J.A Smallwood M.F Causey D Mossop J.R Klucsarits B Robertson S Robertson J Mason M.J Maurer R.J Melvin R.D Dawson G.R Bortolotti J.W Parrish Jr T.F Breen and K Boyd 2009. Why are American Kestrel (Falco sparverius) populations declining in North America? Evidence from nest box programs. Journal of Raptor Research 43:274–282. Google Scholar


K.L Speziale and S.A Lamertucci 2013. The effects of introduced species on raptors. Journal of Raptor Research 47:133–144. Google Scholar


J.L Tella G.R Bortolotti R.D Dawson and M.G Forero 2000a. The T-cell immune response and return rate of fledgling American Kestrels are positively correlated with parental clutch size. Proceedings of the Royal Society of London B 267:891–895. Google Scholar


J.L Tella G.R Bortolotti M.G Forero and R.D Dawson 2000b. Environmental and genetic variation in T-cell mediated immune response of fledgling American Kestrels. Oecologia 123:453–459. Google Scholar


K.L Wiebe and G.R Bortolotti 1992. Facultative sex-ratio manipulation in American Kestrels. Behavioral Ecology and Sociobiology 30:379–386. Google Scholar


K.L Wiebe and G.R Bortolotti 1994a. Energetic efficiency of reproduction: the benefits of asynchronous hatching for American Kestrels. Journal of Animal Ecology 63:551–560. Google Scholar


K.L Wiebe and G.R Bortolotti 1994b. Food supply and hatching spans of birds: energy constraints or facultative manipulation? Ecology 75:813–823. Google Scholar


K.L Wiebe and G.R Bortolotti 2000. Parental interference in sibling aggression in birds: what should we look for? Ecoscience 7:1–9. Google Scholar


L.G Woolaver R.K Nichols E Morton and B.J.M Stutchbury 2013. Nestling sex ratio in a critically endangered dimorphic raptor, Ridgway's Hawk (Buteo ridgwayi). Journal of Raptor Research 47:117–126. Google Scholar


R Yosef S Gomboobaatar and G.R Bortolotti 2013. Sibling competition induces stress independent of nutritional status in broods of Upland Buzzards. Journal of Raptor Research 47:127–132. Google Scholar
The Raptor Research Foundation, Inc.
Russell D. Dawson "A Journey of Raptor Research: Commemorating the Scientific Contributions of Gary R. Bortolotti," Journal of Raptor Research 47(2), 89-95, (1 June 2013).
Published: 1 June 2013

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