Is HARLAN S HAWK a subspecies of Red-tailed Hawk? Review of publications that advocate such and why their taxonomic justifications are not convincing

Transcription

1 Is HARLAN S HAWK a subspecies of Red-tailed Hawk? Review of publications that advocate such and why their taxonomic justifications are not convincing British Columbia Washington harlani William S. (Bill) Clark B. j. calurus

2 HARLAN S HAWK: described as Buteo harlani by Audubon (1830), based on his Louisiana adult specimen. Ornithological Biography i: Type specimen is in the British Museum British Natural History Museum

3 TAXONOMIC STATUS - history : Species: B. harlani : Subspecies of Red-tailed Hawk: Buteo jamaicensis harlani, but without taxonomic justification. AOU 2 nd check-list : Species: B. harlani, with justifications given for separation. AOU to present: Subspecies of Red-tailed Hawk: Buteo jamaicensis harlani, but without taxonomic justification. AOU 1972.

4 1891: AOU check-list committee decided harlani was a subspecies of the Red-tailed Hawk. Apparently based solely on Ridgway (1890), who thought a light-morph adult Harlan s specimen was a hybrid, an adult Red-tail with a Harlan s tail. Light-morph adult Harlan s Hawk - Canadian Museum of Nature Specimen was collected in late September in Iowa. I was unable to locate it. Ridgway s description fits many adult light Harlan s. But even if it had been a hybrid, that does not make Harlan s the same species, as many hybrids exist between good species of Buteo.

5 However, Ridgway in 1895 still treated Harlan s Hawk as a species on page 469 of his: Ridgway, R The Ornithology of Illinois. Part I, volume II. Description catalogue. State Laboratory of Natural History. pp Included descriptions of both light and dark color morphs of Harlan s Hawks and differences from Red-tailed Hawk.

6 1944: AOU reinstated B. harlani, citing Peters 1931 & Taverner Peters (1931) Check-list of the Birds of the World treated B. harlani as a species, perhaps based on the work of Kirk-Swann. Taverner (1936) changed his mind (from Taverner 1927) and argued why harlani is a good species based on plumage differences. Wood (1932) (not cited) described plumage differences between 137 harlani specimens & > 200 of B. jamaicensis and considered Harlan s a species.

7 AOU check-list committee cited three publications to justify its 1973 decision: 1. Brown & Amadon Listed harlani as a race of jamacensis but stated that some considered it a species. 2. Godfrey Birds of Canada. Listed harlani as a race of Red-tail, no reasons given. 3. Van Tyne and Sutton Paper described new subspecies B. j. fuertesi. State that they cannot differentiate between juvenile dark calurus and harlani. NONE offered taxonomic justifications for lumping or rebuttals of separate species arguments given by Taverner, Peters, and Woods.

8 Questioning of this decision Dr. Richard Banks, then chairman of the AOU Check-list committee, gave me copies of four letters regarding this taxonomic decision. Dr. Laurence Jerome wrote a letter in 1974 to the then Chairman of the AOU check-list committee and pointed out the lack of justification for lumping Harlan s with Red-tailed. He noted the lack of reference to Wood (1932) and suggested that the committee review its decision and urge studies to better understand the taxonomy of this taxon.

9 Questioning of this decision The Chairman wrote a long response to Jerome. He offered no taxonomic justifications for this lumping other than this was the accepted taxonomic opinion. He referred to alleged interbreedings between the taxa as a justification, but we now know that this happens regularly between good species and is not in itself a factor in taxonomy. He did not refute the differences mentioned by Wood (1932) or Taverner (1937) nor address the request for further studies. Two other committee members, both eminent ornithologists, also wrote letters to Jerome but offered no further taxonomic justifications.

10 But Harlan s Hawks consistently differ from Red-tailed Hawks harlani Buteo jamaicensis calurus British Columbia British Columbia My presentation listing all of the differences is on The P-Fund s GRIN web site. See next slide for a summary and URL:

11 Harlan s Hawk differs from Red-Tailed Hawk, Buteo jamaicensis calurus, by: 1. Frequency of color morphs; 2. Adult plumage by color morph especially in tail pattern and color; 3. Harlan s adult & juvenile plumages are almost alike; those of Red-tails differ; & 4. Extent of bare area on the tarsus. 5. Some behaviors. For a presentation explaining these differences, go to: ults.asp?lresid=155 And scroll down to Publications and click on pdf after Harlan s Hawk differs

12 Treated as the same species most likely due only to alleged records of interbreeding, as this was the Biological Species Concept of the time. Mindell (1983) showed that Harlan s had a breeding range exclusive of Red-tailed Hawks, and concluded that they were subspecies, based on the citations above. He could just as easily used the same data to consider Harlan s a species. Two citations given as proof of interbreeding: Taverner (1927) and Lowe (1968) Both are based on Alaska breeding adults, with one adult harlani & the other calurus, however both are harlani.

13 HARLAN S IS A VALID SUBSPECIES OF RED- TAILED HAWK Mindell (Auk 1983): Mindell, when a grad student, surveyed for raptors along rivers in west central Alaska for three summers. During the 3rd summer, he noted the tail color of adult Harlan s seen and little else about their plumages (Dark and light circles). >10% All

14 Mindell (1983) He saw 82 adults in 3 rd summer, of which 9 had some rufous in their tails; he called these 9 intergrades based on alleged interbreeding, but all of these were most likely harlani. He offered no proof of interbreeding, but cited Taverner (1927) and Lowe (1968), nor did he present any good taxonomic reasons to support his assertion that this is a valid subspecies. Mindell has since published monumental papers on raptor phylogeny. Important result of this paper: ONLY HARLANI OCCURS IN THAT AREA OF ALASKA! Mindell could also have used his results to justify considering Harlan s as a species.

15 Mindell (1983) cited for interbreeding: Taverner (1927) His alleged calurus specimen breeding in Alaska with a harlani was, upon inspection, also harlani (see previous slide). Same with other alleged interbreedings.

16 Taverner (1927): Family was collected on the Chitina River, AK in July 1925 Chicks harlani 3 chicks Canadian Museum of Nature Adult male is not calurus. It is harlani, with short bare tarsi, as are the 3 chicks.

17 Mindell (1983) cited for interbreeding: Lowe (1978) thesis U. Of Alaska Actually harlani MS Lowes AK calurus & borealis breeding adults differed from those seen elsewhere and were all harlani that had some rufous or banding in tails

18 Plates 5 & 6 of Lowe s Thesis Lowe thought that the dark adult on the right was an adult Western Red-tail, B. j. calurus. But it is a rather typical dark-morph adult Harlan s Hawk. Lowe s records of breeding between harlani & calurus are not valid.

19 Mindell in Auk (1983) and Amer. Birds (1985) believed that harlani was a Red-tail subspecies, apparently based on his seeing rufous in the tails and body plumages of hawks in Alaska, which he thought meant that they breeds freely with neighboring jamaicensis. Many adult Harlan s have some rufous in their tails but have no traits of Red-tailed Hawks of (other) subspecies. Alaska Bob Dittrick

20 Mindell took three nestling Harlan s Hawks from interior Alaska One was a typical dark, one was light, and the third was black; all three were pure harlani! David Mindell He noted rufous in the adult plumages of all three hawks and concluded that there was gene flow between harlani and B. j. calurus. That and his observations of rufous tails in Alaska were the basis for his two papers (1983 & 1985).

21 Adult plumage of Mindell s light-morph hawk David Mindell He noted the rufous in the tail and thought this bird had calurus genes. But there are no calurus traits on this hawk s head, underparts, or tail. It is a typical adult harlani!

22 Adult plumage of Mindell s typical hawk David Mindell He noted the rufous in the breast and thought this hawk had calurus genes. But there are no calurus traits on this hawk. It is a typical adult harlani!

23 Adult plumage of Mindell s dark hawk The underparts of this hawk were uniformly blackish David Mindell He noted the rufous in the tail and thought this hawk had calurus genes. But there are no calurus traits on this hawk s head, upperparts, or tail. All of these are pure Harlan s Hawks

24 Another reason for lumping was that adult Harlan s can show rufous in their tails, that this could only happen by interbreeding, ignoring ancestry & hybridization. Quite a few adult Harlan s show rufous in their tails & no traits of Red-tailed Hawk. My presentation on extreme variation in adult tails is available on The Peregrine Fund web site GRIN: Go to Results.asp?lresID=155 And scroll down to Publications, then click on pdf after Extreme tail variation

25 Adult Harlan s tails can by gray or can have some rufous & are variable British Columbia Adult Red-tails always have all rufous tails with a narrow dark subterminal band and sometimes have other narrow bands MVZ Texas It is possible that the rufous in some harlani tails is due to interbreeding.

26 A recent paper presented some results from sampling DNA (but non-coding areas) of Harlan s and Red-tailed Hawks. Hull et al (2010) Population structure and plumage polymorphism: The intraspecific evolutionary relationships of a polymorphic raptor, Buteo jamaicensis harlani. BMC Evolutionary Biology

27 They sequenced 17 microsatellite loci and 430 base pairs of mt-dna control region of: Western Red-tail (B. j. calurus)(ca & UT) Eastern Red-tail (B. j. borealis)(wi) Harlan s Hawk (harlani) (AK) *B. j. alascensis of se Alaska was not sampled RESULTS: Mt-DNA & nuclear DNA between Harlan s Hawk and two subspecies of Redtailed Hawk differed, but only a little.

28 Hull et al interpreted their results to indicate gene flow betweenthese taxa and concluded that harlani is closer to borealis than to calurus. They also concluded: our findings are inconsistent with the historical description of harlani as a separate species. In other words, they do not reject the hypotheses that harlani is a separate species, they just found no support for such in the DNA they sampled.

29 Hull et al found no differences in the sequences of Mc1r gene among these taxa (only one of many genes that control for color), and they suggested that differences in color morph frequency (harlani mostly dark; other taxa, mostly or always light) could be due to environmental differences. (epigenetic and not due to the many other genes that control color). They did not address the differences in color between harlani (black) and the others (brown) nor that many other genes can control for color.

30 Hull et al. state: The extent of variation makes descriptions of definitive B. j. harlani characters difficult and no diagnostic set of B j. harlani plumage characters has yet been accepted (Liguori & Sullivan 2010). However, Liguori & Sullivan do present characters that distinguish harlani, as did Wood (1932). Hull et al. did not address other differences in plumage and morphology. And also I do so in my presentation: Harlan s Hawk differs which was mentioned previously but was not available to Hull et al.

31 Hull et al included no discussion of the differences in plumages between harlani and the other taxa and did not cite Wood (1932), who described some of these differences. They cited Mindell (1983) for validation of subspecies status of B. j. harlani. Mindell (1983) cited Taverner (1927) and Lowe (1978) for instances of interbreeding. NONE OF THESE ARE VALID CASES OF INTERBREEDING! Examination of specimens in all instances verified that the alleged calurus and borealis were in fact harlani.

32 Finally, Hull et al. conclude by recommending many further investigations: 1. Determine the mechanisms influencing plumage patterns in B. J. harlani, and 2. Identify the gene(s) responsible for variation in the plumages of these taxa, and 3. Determine factors responsible for the dark plumages, and 4. Perform a controlled study on environmental influences on the plumage characters of harlani. In light of the above, this paper seems to ask more questions than it answers.

33 The following articles are useful in interpreting the results from Hull et al. (2010): Winker (2009) advocated using both phenotype (results of natural selection) & genotype (results of time and random mutations) to evaluate speciation. Hull et al (2009) used only genotype. Humphries and Winker (2009) showed that for nine species pairs of Beringia birds, Mt DNA, nucdna, and phenology gave conflicting estimates of divergences due to separation by the rising Bering sea.

34 Irwin et al. (2009) found that two taxa of Eurasian buntings, Yellowhammers and Pine Buntings, which have distinct plumages, had nearly identical sampled mtdna. They hybridize in an extensive zone in western and central Siberia. No one questions that they are both species However, variation in the nuclear gene CHD1Z between them was comparable to that of other species pairs.

35 Gay et al (2009) showed that for two speciespairs of gulls that had significant gene flow and essentially identical mtdna, they nevertheless maintained their species distinctness in active DNA, no doubt because of selection. Glaucous-winged Hybrid Western This is another case of DNA being almost alike in two good species, & much closer than the DNA of harlani & jamaicensis of Hull et al (2009).

36 Brelsford & Irwin (2009) found that two taxa of Yellow-rumped Warblers had identical sampled DNA, but used SNPS to find genetic differences that they related to plumage differences between them on both sides and across a hybrid zone. They advocated two species. Audubon s Warbler Myrtle Warbler From Sibley They identified two nuclear loci (one sex-linked and one autosomal) that showed fixed differences across the hybrid zone, in a close concordance with patterns of plumage variation.

37 In many of these studies, the MtDNA was identical or nearly so between the two species reported, but in the results of Hull et al (2010), the mtdna was not identical. Their results are: For mtdna: the various Φst are: 0.203* between harlani & calurus 0.059* between harlani & borealis 0.032* between calurus & borealis * All three were significantly different. Bottom line: it takes only a few differences in important genes to reflect assortative mating between taxa.

38 From Dice 1932: According to the usual geographic concept of subspecies employed by zoologists, no two subspecies of the same species should, except under extraordinary conditions, occur in the same area; for if they should occur together they would be expected to interbreed and lose their distinctness.

39 Breeding Ranges Harlan s Hawks breed in Alaska, Yukon, nw BC, and the far north of NWT. The ranges of five (other) subspecies of Red-tails are shown. Mixture From Wheeler 2003, with modifications harlani

40 HOWEVER, Light-morph Harlan s Hawks are & have been breeding within the calurus range in western Canada Based on specimens, sightings, and photographs taken at nests Alberta BC

41 HARLAN S HAWKS ARE & HAVE BEEN BREEDING WITHIN THE RED-TAILED HAWK RANGE IN WESTERN CANADA For a presentation explaining the extent of overlap in breeding, go to: rcherresults.asp?lresid=155 And scroll down to Publications and click on pdf after Harlan s Hawk are & have been

42 And Red-tails occur in the Harlan s breeding range 2X Adult lightmorph calurus sighted in late spring and summer April X Atlin July

43 Red-tails in Harlan s breeding range Apparent Red-tailed Hawk nesting in Alaska. This adult was nesting near the Hawk Count site at Gunsight Mt., AK. Brian Sullivan noted that it was a male breeding with a light adult female Harlan s. His plumage is similar to Red-tails in NWT & Alberta (Sullivan 2011). Adult was a typical light adult Harlan s, with whitish head, underparts, & upper tail. It was the only light adult seen by Brian that trip. Brian Sullivan

44 Dark Red-tailed X dark Harlan s in se AK Chuck Susie found a pair of dark adults breeding near Klukwan, se Alaska in June The male was a dark-morph Harlan s and the female was a dark-morph red-tailed Hawk. No dark morph is known for B. j. alascensis. Chuck Susie Adult male Adult female Juvenile One of two juveniles was decidedly Harlan s Hawk

45 Some hybrids exist between Harlan s & Redtailed Hawks, but there is no classic hybrid zone, e.g., as shown by Glaucous-winged & Western Gulls & Yellow-rumped Warblers and other good species pairs. Glaucouswinged Gull Also, can two subspecies be breeding in the same areas? Hybrid zone From Gay et al 2009 Western Gull

46 One possible scenario for the origin of harlani is that it was isolated from jamaicensis during the last glacial maxima, most likely in Beringia, & evolved in isolation to look and act differently. Nothing in the Hull et al (2009) results rules out this scenario for the evolution of Harlan s Hawk.

47 Harlan s Hawk As the glaciers retreated, most likely secondary contact occurred with one or more of the subspecies of B. jamaicensis, with some resulting hybridization. If the resulting gene flow were unrestricted, then one would expect that both forms would share traits and look much more alike, most likely with a hybrid zone between their breeding ranges. Clearly this isn t happening. Something is causing the majority of Harlan s to be dark and their plumages to differ, and that most likely is selection, either natural or sex-linked or both, resulting in assortative mating.

48 Hybridization Many good species hybridize, for a variety of reasons. This is especially true in the genus Buteo, in which many species pairs have been reported hybridizing, some on a regular basis. Red-tailed Hawks have been found to hybridize with: Swainson s Hawks, Red-shouldered Hawks, Ferruginous Hawks, & Rough-legged Hawks.

49 Hybridization Hybridization between harlani and several taxa of B. jamaicensis is happening, but it is not resulting in the widespread mixing of characters between them or in a classic hybrid zone at the junction of their breeding ranges. Further study of this hybridization will help us understand the true taxonomic relationship between these taxa.

50 HARLAN S HAWK SPECIES STATUS Harlan s Hawk is clearly much more different from the various subspecies of Red-tailed Hawk than they are from each other. Harlan s Hawk differs from Red-tailed Hawk more than any two subspecies of any other raptor species. The BOU (see below) and the adherents of the Phylogenetic Species Concept both would have no problem assigning species rank to Harlan s Hawk. I plan to publish my findings on phenotypical differences and will assist any and all analyses of genetic differences.

51 Criteria for determining if a taxon is a species The American Ornithological Union (AOU) has no criteria for judging species status. But Helbig et al (2002) have published criteria of assigning species rank that have been accepted by the British Ornithological Union. These are: 1. Are the taxa diagnosible? 2. Are they likely to retain their genetic and phenotypic integrity in the future?

52 Criteria for determining if Harlan s Hawk is a species 1. Is Harlan s Hawk diagnosably different from Red-tailed Hawk? The answer is a clear YES. 2. Is Harlan s Hawk likely to retain its genetic and phenotypic integrity in the future? There are no reasons to assume that Harlan s will be subsumed into Red-tailed Hawk in the primary breeding range of Alaska and Yukon, as it has not done so in the past.

53 FUTURE RESEARCH DNA researchers should locate and sequence the genes that are causing these differences and compare and relate their phenotypes and genotypes to get a clearer understanding of the taxonomic status of Harlan s Hawk. We also need to better understand why light Harlan s are breeding in the western Canadian range range of calurus and why a few adult calurus occur in the breeding range of harlani.

54 LITERATURE CITED: AOU Thirty-second supplement to the Check-list. Auk 90:414. Audubon, J. J Birds of America, Folio ed., Plate 86. Brelsford, A., & D. Irwin Incipient speciation despite little assortative mating: the yellow-rumped warbler hybrid zone. Evolution 63-12: Brown L. H., & Amadon, D Eagles, Hawks, and Falcons of the World. Vol. 2:606. McGraw-Hill, New York. Dice, L. R The Occurrence of Two Subspecies of the Same Species in the Same Area. J. Mammalogy 12: Gay et al Speciation with gene flow in the large white-headed gulls: does selection counterbalance introgression? Heredity 102: Godfrey, W. E The birds of Canada. Rev. ed. Natl. Mus. Nat. Sci., Ottawa, ON. Helbig, A. J., A. G. Knox, D. T. Parkin, G. Sangster, and M. T. Collinson Guidelines for assigning species rank. Ibis 144: Hull, J. et al Population structure and plumage polymorphism: The intraspecific evolutionary relationships of a polymorphic raptor, Buteo jamaicensis harlani. BMC Evolutionary Biology 10:224. Humphries and Winker Discord reigns among nuclear, mitochondrial and phenotypic estimates of divergence in nine lineages of trans-beringian birds. Molecular Ecology Irwin, D. E., A. S. Rubtsov, and E. N. Panov Mitochondrial introgression and replacement between yellowhammers (Emberiza citrinella) and pine buntings (Emberiza leucocephalus) (Aves: Passeriformes). Biol. J. Linnean Soc. 98: Liguori, J., and B. L. Sullivan Comparison of Harlan s Hawks with western and eastern Red-tailed Hawks. Birding 42: (Continued)

55 LITERATURE CITED (Cont.) Lowe, C. M Certain life history aspects of the Red-tailed Hawk in central Oklahoma and interior Alaska. MS thesis, U. of Alaska. Mindell, D. P Harlan s Hawk is a valid subspecies of Red-tailed Hawk. Auk 100: Mindell, D. P Plumage variation and winter range of Harlan s Hawk (Buteo jamaicensis harlani). American Birds 39: Peters, J. L Check-list of birds of the world, vol. 1. Harvard Univ. Press, Cambridge, MA. Ridgway, R Harlan s Hawk a race of the Red-tail, and not a Distinct Species. Auk 7:205. Ridgway, R The Ornithology of Illinois. Part I, volume II. Description catalogue. State Laboratory of Natural History. pp Sullivan, D Apparent Eastern Red-tailed Hawk nesting in Alaska. North American Birds 65(3) 1-4. Sullivan, B. & J. Liguori A territorial Harlan s Hawk (Buteo jamaicensis harlani) in North Dakota, with notes on summer records of this subspecies from the northern Great Plains. No. Am. Birds 64: Taverner, P. A A study of Buteo borealis, the Red-tailed Hawk, and its varieties in Canada. Victoria Mem. Mus. Bull. No. 48 Biol. Series 13:1-25. Taverner, P. A Taxonomic comments on Red-tailed Hawks. Condor 38:6 Winker, K Reuniting Phenotype and Genotype in Biodiversity Research. BioScience 59: Van Tyne, J., and G. M. Sutton The birds of Brewster County, Texas. Misc. Publ. Mus. Zool. Univ. Mich. No. 37:20. Wood, N. A Harlan s Hawk. Wilson Bull.44:78-87.

56 Thanks The following people made helpful comments on earlier drafts of this presentation: Richard Banks, Donna Dittman, Darren Irwin, Jim Lish, Brian Millsap, Van Remsen, Ildiko Szabo, Kevin Winker, & Chris Witt. David Mindell kindly shared his photos and information. Bob Dittrick, Chuck Susie, and many others freely shared their photos of these taxa with me.

57 Thanks I thank with great enthusiasm the many curators and collection managers for permission to look at and study their bird specimens and for their freely given help, especially the Canadian Museum of Nature and Michel Gosselin, but also Mark Robbins (KU) and Robert Prys- Jones (British Museum). Theirs is a most valuable and important resource for bird study.

58 THANKS FOR YOUR ATTENTION Thanks also to The Peregrine Fund (especially Lloyd Kiff & Travis Rosenberry) for making this presentation available on their Global Raptor Information Network (GRIN) web site