buteo polyosoma y buteo poecilochrous

8/17/2019 Buteo polyosoma y Buteo poecilochrous

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AXONOMIC AND PLUMAGE RELAIONSHIPBEWEEN REDBACKED BUZZARDS Buteo polyosoma

AND Buteo poecilochrous

José Cabot1 y jitte de Vries2

1 Estación Biológica Doñana. C.S.I.C. Avda. Américo Vespucio s/n 41092 Sevilla, Españ[email protected]

2 Escuela de Ciencias Biológicas, Pontificia Universidad Católica del Ecuador, Casilla 17-01-2184,Quito, Ecuador

[email protected]

INRODUCION

Te Gurney‘s Buzzard Buteo poecilochrous and the Variable Buzzard B. polyosoma are twoclosely related neotropic species (Lerner et al.,2008). Te first is found all along the Andeanchain from Colombia to the north of Argen-tina y north of Chile, and always above 3000m in altitude. Tis species occurs in habitatslike open paramos, mountain ridges and al-

tiplano, with the exception of an establishedpopulation at 2000 m above sea level andrestricted along the borders of the Loa river, which in a deep canyon crosses the Atacamadesert in the Antofogasta region in Chile, atthe limit of its south western distribution. According to Lehmann (1945) this speciesoccupies in SW Colombia also an altitude ofaround 2000 m, but Cabot et al. (2006) haveindicated that these specimens refer to the White-tailed Buzzard , B. albicaudatus .

Buteo polyosoma , in contrast, has a more

extensive distributional range from the westof South America, from Colombia to the ex-treme south of the sub continent, includingthe Falkland Islands and the Juan Fernándezarchipelago.

Gore y Gepp (1978) indicate that B. polyo-soma is rare in Uruguay and Reichholf (1974)mentions this species for NW Brasil.

B. polyosoma occurs in a great variety ofhabitats in a wide altitudinal range (Cabot,1991; Jiménez, 1995) preferable xerophytic

regions with different climatic and physicalconditions, including high Andean altitudes4000 m, Andean valleys and mountain slopesto the low level plains of El Chaco and thepampas region, as well as southern Chile and Argentina.

MAERIAL AND MEHODS

Te present study is based on the exa-

mination of feathers and body measure-ments taken from nearly 500 skins of bothspecies, from collections in European andSouth American museums (mentioned inthe acknowledgement section). Since 2000the moult process was observed by JC, onB. polyosoma (four birds) and B. poecilochrous (six birds), legally imported from Peru, onthe changes in plumage from specimens ofButeo polyosoma (four) and B . poecilochrous (six). Also four chicks of B. polyosoma, hat-ched in captivity in 2008, were observed over

the years. Field data was taken in irregularpatterns in Ecuador, Peru Bolivia and Chilefrom 1981 until 2008. Te specimens weresexed by body measurement and moleculartechniques (Ellegren, 1996).

Te taxonomic affi nities study was se-quenced in one segment of 620 bases of thecytochrome b mitochondrial DNA followingstandard procedures. Identification was accor-ding the measurements and details mentio-ned in Cabot y de Vries (2003).


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RESULS AND DISCUSSION

A complex taxonomic history

Te history of the taxonomic relations between the two species is long and controversial. raditionally, these two forms have been con-sidered separate species, albeit closely related.However, they have also been considered asco-species, in other words different at thesub-species level, but in neither case has therebeen any fundamental back-up to justify the-se designations of status. Brown and Amadon

(1968) point to the altitude variant to distin-guish one f rom the other. At present, they arerecognised as two separate species based onthe biological species concept (Cabot and deVries, 2003; 2004).

Te reasons for this long taxonomic deba-te are varied and basically stem from:

Te high variability in plumage in both•species due to ontogenical changes ofplumage depending on sex, morph andage over a period of six years, complica-ted further by males acquiring tempora-

rily similarities with the female plumage.Some patterns are very similar betweenthe two species (Vaurie, 1962; Cabotand de Vries, 2005). Te lack of valid criterion to determine•the specific difference, in the hand as well as in the field. Te non-familiarity, of the taxonomists•involved, with these species, and thescarcity of a series to determine the se-quence of changes of the plumages ofspecimens in ornithological collections.

Te overlapping geographic ranges and• altitudes, body measurements and theplumage patterns occurring in thesespecies added to the debate.

Te first species described was B. polyoso-ma from an adult male dark morph specimenoriginating in the Falklands (Quoy and Gay-nard, 1824). Several authors have treated thetaxonomy e.g. Hellmayr, 1932; Johnson, 1945;Housse, 1945; Lehmann, 1945; Vaurie, 1962;

Brown and Amadon, 1968; Farquhar, 1998;Cabot and de Vries,200; the latter consideringbiological and ecological aspects). Tree sub-species in B. polyosoma have been discussed, B. p. polyosoma, B. p. peruviensis, B. p. exsul , the la-tter confined to the Juan Fernández Island.

Te complicated and tortuous roadtowards the systematic relationship started55 years later with the description of Buteo poecilochrous Gurney 1879. A larger species, in which there is a considerable overlap in somemale body measurements, compared with the

B. polyosoma females. wo subspecies havebeen described for B. poecilochrous. Te nomí-nate form and B. p. felsai from northern Peru,Bolivia, NW Argentina and Chile (Cabotand de Vries, 2009).

European and North American orni-thologists, who were partially or completelyunfamiliar with these species in their naturalenvironment, only had a few skins available inmuseums, which represented, in a small andincomplete way, the complex plumage mosaicproper to these strongly polymorphic species.

Te taxonomists were faced with a complexdiversity of shapes, designs and sizes whichconsisted of a heterogenic sample with ele-ments which were diffi cult to understand andclassify. Even if some plumages were duplica-ted in the series of museums, others could beabsent and, at the same time, similar plumages were found in specimens of different sizes.

In addition, it was found that specimensof both species could have the same or simi-lar geographic origin, or that within the se-ries there might be specimens whose sex hadnot been determined or wrongly determined,(even by the collector), as well as a considera-ble number of males classified as females ( Ji-ménez, 1995; Cabot and de Vries, 2003), sincethey carried the red dorsal patch characteris-tic of the definitive plumage of adult female(Vaurie, 1962). However, this characteristic isalso present in immature males (Pávez, 1998;Cabot and de Vries, 2004).

Examples from other species, wronglyclassified as B. polyosoma or B. poecilochrous ,


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have been found in outstanding scientific co-llections from Europe. Inter alia: B. swainso-ni , B. ventralis, B. albicaudatus and B. albigula , which were presumably used in taxonomicstudies of red-backed buzzards.

Unfortunately, the criteria devised by thetaxonomists only complicated matters further.One of these, the one which was the most widely disseminated, is known as the Strese-mann rule (1925). Tis criterion became theonly guideline available to ornithologists toseparate B. poecilochrous from B. polyosoma . It

is based upon the relative distances betweenthe tips of the third and fifth most externalprimaries: longer in B. polyosoma than in B. poecilochrous . Our results have shown that thisrule is not met in B. poecilochrous (Cabot andde Vries, 2003), since in this species both fea-thers are practically the same and, in nearlyhalf the specimens, the third primary is muchlonger than the fifth. Tere are even specimensthat have one formula for one wing and thereverse for the other, as in the case of the typespecimen. In this way, the same individuals

were classified and reclassified several timesover, according to the criterion of the orni-thologist (Vaurie, 1962), as has occurred withsome paratypes of Chilean origin of the subs-pecies B. poecilochrous feldsai , recently descri-bed by Cabot and de Vries (2009), specimensreferred in Hellmayr (1932), Hellmayr andConover (1949).

Another criterion used in the study ofplumage was the difference in categories foradults and for juveniles according to the pa-ttern of the markings and the coloration ofthe tail (Farquhar, 1998). Birds with a whitetail and a subterminal black band were consi-dered adults, and those with a greyish-browntail with irregular dark lines, juveniles. Tisseparation does not match up to reality sincethe subadults (also with a white tail) are con-sidered as adults, ascribing a greater degreeof polymorphism to the latter than is in facttrue. Tis made it diffi cult to study plumageand to understand the differences betweenthe species.

For a long time, South American ornitho-logists with direct knowledge of both forms,have been asserting that the plumage of B. polyosoma and B. poecilochrous are the result ofa plumage succession pattern relating to age,from the first basic plumage of the juvenileto the definitive adult plumage with differentpatterns in the sequences, according to morph,sex and age (Housse, 1945; Lehmann, 1945;Goodall et al., 1951; orres-Barreto, 1986). Tis occurs also in other related species B al-bicaudatus (Lehmann, 1945; orres-Barreto,

1986; Johnsgard, 1990) and Geranoaetus me-lanoleucus (Hudson, 1945; Lehmann, 1945;Goodall et al., 1951; Johnson, 1965; Jiménez y Jaksic, 1990). Tese results were not widelycirculated internationally since they were pu-blished in Spanish. Because of this, later stu-dies were made without taking into accountthese results, for example the recent studyby Farquhar (1998) which attributes pluma-ge variability to chance; while, at the sametime, Pávez (1998) describes in detail an or-dered sequence of changes in plumage, sub-

ject to a pattern, from juvenile to adulthood. Te suggestion of con-specificity between B. polyosoma and B. poecilochrous based on a cli-mal gradient of size depending on altitude(Farquhar, 1998) should not be taken intoaccount. Tis gradual change does not exist(Cabot y de Vries, 2003).

Each species shows characteristic morpho-metric values and has its own ranges whichgive it different proportions (de Vries, 1973), which is also the case at high altitudes over3.800 m at the Altiplano in Bolivia (Cabotand de Vries, 2003). So far no intermediateforms are known, in museums or in the field.Cabot and de Vries (2003) demonstrate thatspecimens from the Andean Altiplano above3800 m are morphologically different fromB. poecilochrous and, moreover, B. polyosomaat the Altiplano are of smaller size than theirconspecifics at lower altitude in the FalklandIslands. Also, no gradient in size and in clinalprocess in body sizes have been detected inspecies of the genera of Geranoaetus, Buteo,


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Falco, Circus , which occur at high Andean al-titudes as well as in the lowlands.

In order to disentangle the systematicrelations between similar taxa, an accurateidentification of each one of the specimens which represent these taxons is required. Inthe case of B. polyosoma and B. poecilochrous ,incorrect identification of the individuals hasbeen the core of the long and distended de-bate between these two species.

Buteo polyosoma and B. poecilochrous areidentifiable by body measurement, by plu-

mage pattern as well as by its silhuette andflight. Te specific differences in morphology(measurements, plumage patterns and per-centage of color morphs), ecologic aspectsand behavior, represent biological barriers which favor specific isolation between bothforms.

Cabot (1988, 1991) found both speciescoexistent in the puna region in northern Bo-livia. B. polyosoma wintering in this area showsa solitary behavior and occurs in mainly flatareas, whereas B. poecilochrous is sedentary, li-

ving in pairs and is distributed in hilly country, with ridges and gorges. Similarily JC foundthis coexistence in the Atacama dessert nearCalama, Chile, where B.polyosoma occured ina xerophytic hábitat and B. poecilochrous in theoasis of the river Loa

Distinct species of recent origin

Mutations in the sequences of DNA ba-ses of the mitochondrial cytochrome b, be-cause of its constant mutational rate, cons-titute a biological clock which quantifies the

period of time taken to differentiate betweenthe biological forms under study. Te rate ofsubstitution of nucleotides is assumed at between 2% and 10% per million years (Irwinet al., 1991). It could be assumed that theolder the genetic divergence of the forms,the greater the biological differences shouldhave been between them. Nevertheless, it isnot always so; selective pressures can act in aqualitative and quantitative differential way,upon the organisms in very short distances

in mountain ecosystems (Fjeldså, 1992). Teeffect of a differential pressure from the na-tural selection between the populations andthe variability in the flexibility of adaptationof the organisms, as a response to this pre-ssure, will mould the populations differently.

Riesing et al. (2003) state that, accordingto analysis of a segment of mitrochondrialDNA of 606 bases of cytochrome b, B. po-lyosoma and B. poecilochrous have identicalsequences. We have obtained similar resultsover one sector of mitochondrial DNA with

620 base pairs that B. polyosoma and B. poeci-lochrous have identical sequences , also ofthe same material and similar bases number. Te specimens, two examples of B. polyoso-ma peruviensis and four B. poecilochrous, wereobtained from Peru. Te results indicate thenonexistence of intraspecific variation in thefirst species.

Tis results is not an indicator of co-spe-cificity (as assumed by Farquhar, 1998 andRiesing et al., 2003), but that the evolutio-nary process of speciation has been very re-

cent and has not yet left its mark on the chainof nucleotides of the cytochrome c, due to itsscant variability (Haring et al., 1999).

Analysis carried out on fragments of thepseudoregion control (), which has a grea-ter mutational rate, shows inter-specific di-fferences in the sequences, which in passingalso shows a close affi nity of both species toB. albicaudatus, with which they constitutea definite cluster (Riesing et al., 2003). Te variations in the pseudoregion control finelyreflect the evolutionary processes within thegenus Buteo (Riesing et al., 2003).

Lerner et al. (2008) found genetic supportin the CR_1 control region for independentorigins of polyosoma and poecilochrous fromalbicaudatus , thus supporting their status asdistinct species.

Te hypothesis on the speciation of B. po-lyosoma and B. poecilochrous relates to a recentparapatrics respective differentiation starting with B. albicaudatus. Tese situations arecommon in the speciation process of High


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Andean ornithofauna (Garcia-Moreno andFjeldså, 2000).

In the southern Colombian Andes,B. albi-caudatus reaches medium altitudes (Lehmann,1945) and its diet is centred on rabbits Syl-vilagus brasiliensis, similarly, B. poecilochrousalso bases its diet on this prey. Additionally,in this zone it is the only place where B. al-bicaudatus shows sexual dimorphism with agreater expansion of red over the shouldersof the females, and even over the back (Leh-mann, 1945). Tis points to the latter form

becoming different starting with B. albicau-datus , when it ascended and adapted to highaltitude areas, free of ice after the last ice age,a few millennia ago, and inhabited the uppermountain levels following S. brasiliensis, which is very common in the paramo.

In fact both species of buzzards are verysimilar in size and plumage, especially in thepattern of the ventral parts of the dark morph,(Figure 5 in Cabot and de Vries, 2005). Tissimilarity is mentioned by Gurney in the des-cription of the type specimen B. poecilochrous .

As a matter of fact, three study skins of B. poecilochrous , deposited in the museum ofStockholm, collected at Pichincha and Anti-sana (Ecuador) between 11.500-12.000 feet, were identified by Lönberg and Rendhall(1922) as B. albicaudatus . In this same mu-seum a specimen of B. albicaudatus (NHRM568608) was identified as B. poecilochrous ,collected by Sneidern at Rio imbio, Cauca,Colombia.

Buteo polyosoma could have originated inmedium altitudes starting with those formsderiving from B. albicaudatus, already red-backed, which were climbing the slopes;spreading towards the south, reaching theextreme south where the ice was melting atthose latitudes, and benefitted by the advanceof mammals of Nearctic origin, reaching thesouth of the subcontinent. Tis species colo-nized the Falklands and diversified in somepopulations, as in the case of B. polyosoma pe-ruviensis which inhabits the coastal desert ofPeru and southern Ecuador.

Plumages Te two species of red-backed buzzards

are sexually dimorphic in their two formsof coloration: light and dark (Cabot and deVries, 2004). One outstanding fact (unusualin the Buteo genus) is that both species takesix years to acquire their definitive plumage. Tis occurs in both coloration morphs andadheres to patterns depending on sex andage (Pávez, 1998; Cabot and de Vries, 2004,2009). In this process in both species, suba-dult males acquire in both morphs (light and

dark) red dorsal patches, similar to the fema-les in their definite plumage. All the femalesshow in the definitive plumage the upperpartsgrey with an extensive brick-red dorsal patchin the mantle, whereas for all the males in thedefinite plumage the mantle is dorsal grey(Cabot and de Vries, 2005).

Te B. poecilochrous dark morph specimensare more common than pale morph specimensand this relation seems to occur all along itsrange of distribution. B. polyosoma dark mor-ph specimens are very rare and infrequent

in relation to the light morph, but increasesto the extreme south of its range (Reynolds,1938). Certain plumage patterns of the darkmorph related to age and sex were consideredaberrant forms by Housse (1945).

Te converging of plumages between B. polyosoma and B. poecilochrous of the same sex,age and coloration morph is remarkable. Plu-mage repetition also occurs in both morphsof B. albicaudatus, with small variations. Tislong delay in acquiring definitive plumage isalso manifest in Geranoaetus melanoleucus (Le-

hmann, 1945; orres-Barreto, 1986; Jiménezand Jaksic, 1990; Goodall et al ., 1951; Hud-son, 1945; Johnson 1965) closely related to the White-tailed buzzards (Riesinget al., 2003). Anunusual plumage of Geranoaetus melanoleucus isidentical to the adult definitive pale morph ofB. albicaudatus (Cabot and de Vries, 2008b).

In both species, there are three stages inthe process for changing plumage:

Juvenile: first and second calendar year. Tey show very different plumages from the


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adults and subadults. At this age there existsalready sexual dimorphism in plumage color.Males in their basic background plumageshow more uniform plumage and with darkerbackground with fewer paler marks than fe-males, which show warmer brown plumages, with clear markings, but less pale as in males,in upper as well in lower parts. Juvenile fe-males, especially in B. poecilochrous , have thesmall feathers of the bend of the wing and theborder of the tail feathers, reddish, a characte-ristic not found in juvenile males.

Pale morph, underparts: brown markingson a whitish creamy to tannish cream back-ground, brown or greyish brown tail with na-rrow, transversal, irregular blackish bands.

Dark morph, underparts: uniform brownto black brown background with pale mar-kings; tail as above.

Immature: Teir plumage becomes similarto the definitive plumage of the adult femalebut the background colour on upperparts isgreyish brown, not pure grey as in the adult. Te males show pale reddish patches on the

mantle (and also a reddish or brown reddishfeathers in median lowerparts in the darkmorph). Tey imitate the females in the samephase, but always with less purity and richnessof color and less surface and defined area.

Te subadult females are extensivelyerythristic, as though trying to distance them-selves from the males who are imitating them. Tey show an extensive red dorsal patch whichspreads to the flanks and neck sides (palemorph) until the neck or under parts extensi- vely red or brown red (dark morph). Tese arebirds in their third and fourth livery.

Adults: Te sexual dimorphism is accen-tuated.

Males: A tendency to differentiate fromthe females. Tey show a uniformly grey back with white underparts (pale morph) or mainlygrey (dark morph): usually smooth and uni-form coloring without markings in B. polyoso-ma, and strong white and grey barring usua-lly in B. poecilochrous along the flanks, thighs,

belly and undertail coverts. However someB. poecilochrous specimens have upper andmedian underparts uniform grey with some whitish marks on flanks, thighs, and grey and white upper and undertail coverts.

Females: Extensive red dorsal patch. Whi-te underparts in pale morph females, as forthe males in the same phase. Dark morph B. polyosoma females show uniform grey upper-parts with a red breast band usually withoutmarks on under parts. B. poecilochrous femaleson the other hand, have no red band in their

definitive plumage and the under parts are si-milar to the males in the same phase.

Te significance of polymorphism

Te significance of the delayed matura-tion process in these two species and betweenother related buzzards remains a mystery.

Te coloration differences between sexesand ages in B. poecilochrous may be related tothe coexistence of several individuals within arestricted area and with high food availability.

Individual variations in the duration of

this process may occur which is frequent inprocesses of delayed maturation, but this ispoorly known. We have observed in somestudy skins some feathers corresponding totwo earlier phases, more easy detectable inimmature birds and new adults. Tese indivi-dual variations need further studies, but maybe related to stress in subadult males withfemale characteristics, in situations of domi-nancy and hierarchy.

De Vries ( pers. obs .) has observed that juveniles enter those territories, where they

were born the previous year, without aggre-ssion, and are fed by their parents who at thetime are breeding growing chicks. Also, thereare breeding females, which have not reachedtheir definitive plumage. (Solís and Black,1985; Coello, 1997). Tis has been provedin dark morph birds which are easily distin-guishable by their reddish breast band. Tis ismore diffi cult to detect in females of the lightmorph as both in subterminal and definiteplumage the ventral part is white.


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Te reproductive behaviour observed ingroups of up to five individuals could explain why subadult males take on the appearance offemales in order to minimize aggression andto cooperate in the breeding process in viewof the scarcity of territory. Tese helpers areassumed to be male, because of their plumage,although in one case at least there appears tohave been one other female in addition to thereproductive female. Tese were not sexed bymeasurement or molecularly.

Tese observations on several helpers were

carried out in Ecuador. Tere are no similardata available for other Andean areas, Bolivia,Northern Chile and Argentina, where thereare no Sylvilagus brasiliensis.

In B. poecilochrous males which form partof pairs have a grey mantle as do alpha malesliving with male helpers, but also red-backedimmature males may be present in the sameterritory (Solís and Black, 1985; Coello,1997; and field data). Also red-backed males were observed together hunting along theriver Loa (northern Chile), where hunting

grounds are restricted along the borders ofthe river, an oasis in this desert region. Testudy skin (MCINB 199) in the Natio-nal Museum Bolivar in Ambato (Ecuador) with grey and red feathers on the back is anexample of a male loosing the red feathers ofthe mantle. Birds in Bolivia (EBD 6917 andBMNH 1902.318. 1601) are grey mantled with just one grey-red feather what couldindicate a quicker molt where no gregarinesis known.

Male helpers may therefore remain for alongtime red-backed, whereas other males will have the normal and quicker sequency inmolting to the definite plumage.

Gregarious behaviour has not been seen inB. polyosoma . Also its diet is more varied, andthe availability of food in its wide and diver-se distribution area can be subject to seaso-nal changes. Tere are also cases of subadultbreeding females (Reynolds, 1935).

B. polyosoma nests in pairs, so far no groupshave been observed, except for some threeso-

mes defending a territory (Alvarado and Fi-gueroa, 2006). In captivity stressed males re-main with red feathers on the back, dominantmales are completely grey.

It remains to be discovered if the dura-tion and sequence of changes is subject toindividual changes which can be shortened,lengthened or the process arrested, as occursin some species. Te potential effect exercisedby social factors, such as the size and compo-nents of the reproductive group, also needs tobe investigated.

Plumage recognition of B. poecilochrous and B. polyosoma

We have described and illustrated theplumages of B. polyosoma (Cabot and deVries, 2004) and B. poecilochrous (Cabot andde Vries, 2005, 2008) with comments on spe-cific plumage patterns; in spite of the highindividual and geographic variability of theplumages, especially and still for describingfor B. polyosoma. In this work we give theplumage patterns features, of more detailed

form, according coloration morph, age andsex (able 1). Te ontogenic process of plu-mage variation for dark male and dark femaleis showed for B. polyosoma (Figures 1, 2) andfor B. poecilochrous (Figures 3, 4).

Recognition in the field

Te species are recognisable by their si-lhouette (Cabot, 1991; Fjeldså and Krabbe,1990). Identification is helped by knowingthat B. poecilochrous is gregarious or usually fliesin pairs along mountain rock faces or peaks

and is found in high altitude ecosystems, whe-reas this is not the case with B. polyosoma. Tere could be further complications

with identification of wandering or solitary juveniles since their morphology differs fromadults, with a proportionately larger tail inboth species.

B. poecilochrous circles and forms a cha-racteristic dihedral angle with its wings. Te wing beats are slow and profound (Pávez,2005), hovering frequently when hunting in


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Age B. polyosoma B. poecilochrous

1 year basic

Very variable. Upper-parts brown with white-cream to buff markings on wing-coverts and with dark barring on greatercoverts, primaries and secondaries. Sideof head, supercilium and under-partspale cream to tawny. Obvious dark-

brown malar stripe. White throat with variable black streaking; sides of neck with brown tear-shaped markings;central under-parts with rusty-brownarrowhead markings that become morespaced out towards thighs and belly;markings of the same colour on under wing-coverts. ail grey-brown, normally with thin, irregular dark barring. Fema-les are more mixed in colouration and with warmer tones than males.

Variable. Bigger and otherwise similar toequivalent in polyosoma . Brown upper-parts with uniform and darker mantle, pale to buffmarkings on scapulars and tertials. Sides of

head (including subocular area and ear-coverts) and rest of under-parts whitish tointense buff-cinnamon with rusty to dark-brown markings. Noticeably long tail withgrey brownish ground colour and more regu-lar dark barring. Males are more uniform anddarker, but with fewer, paler markings than infemales, which usually have warmer plumagetones and feathers edged in buff-cinnamon.

2nd calendar year

Variable. Similar to preceding plumagetype. Paler and upper underparts cream whithish more uniform; centre of chestand belly variabily barred or reticulatedin rusty- orange to brown; females aremore heavily marked. Te markingsget smaller and more spaced out on thethighs and under-belly. Wing under-coverts with markings of the same co-lour. Grey-brown tail with fine, blackishirregular transversal lines.

Variable. Similar to the equivalent in polyoso-ma , but with the sides of the head with moreextensive pale colouration. Same patterningon under-parts, but browner, from cinna-mon-brown to dark chestnut (occasionallyrusty brown) and generally less rusty thanequivalent in polyosoma. Te ground colourof the under-parts ranges from creamy whiteto cinnamon. Females are generally moreprofusely marked on under-parts and areoften washed with buff-cinnamon. Greyish

tail with regular dark barring.

able 1. Plumage recognition of B. poecilochrous and B. polyosoma .

DISINCIVE FEAURES IN PALE MORPH


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Immature

Variable. Head brown to darkgrey-brown with sides with white streaking. Whitish-cream underparts, rustybarring on centre of chest and thighs.Sides with rusty wash; rusty-brownmarkings on wing under-coverts.Brick-red patch, variable in size, onmantle that in females can merge into

scapulars and tertials. Rectrices whiteand spotted with grey-brown at tips;rectrices also with fine transversal linesabove a black subterminal band, whichis sometimes incomplete.

Variable. Crown blackish brown with andpale sides to head. Back brown with purereddish (or mixed with brown) patch.Scapulars with profusion of pale cream-to-buff markings; tertials with contrastingbarring towards tips, also on upper side ofthe secondaries and primaries. Wing andmedian coverts similarly barred in femalesand sometimes in males. Te barring on thesefeathers is obvious when the wing is closedand remains a constant feature in successive

plumages in both colour morphs in this spe-cies. Under-parts cream-white to buff withchestnut-brown barring in the centre of thechest, but barring more spaced out and fineron belly and thighs. Under wing-coverts with chestnut-brown markings. Rectrices si-milar to equivalent, but more grey tinged and with the transversal barring usually thickerand blacker.

Pre-definitive

Variable. Head brown to brown greyish-

and brown-black, with rest of upper-parts brown-grey, but more uniformand appearance and less barred than inequivalent plumage in B. poecilochrous . White under-parts with dark marks incentre of breast, flanks and on under wing-coverts. Female more denslybarred underneath and with more ex-tensive mantle patch, which reaches thenape and merges into the sides of neck,chest and flanks.

Variable. op of head black to grey-black with white cheeks and the rest of the upper-parts grey-brown to dirty grey, with fewerpale markings; dorsal patch like the equiva-lent plumage in polyosoma , but often exten-ding to scapulars, rump and tertials. In malesthe dorsal patch red with intermixed darkmarks restricted to the upper mantle. ertialsdistally dark barred. Uppertail coverts whitedark barred

Definitive

Variable. Male. Crown and upper halfof sides of head mid-grey to more purepale grey. Upper-parts more uniformand under-parts purer white than inprevious plumage. Barring and greymarkings on sides. Female similar, but with darker back.

Variable. Male similar, but with steel-greyto slate-grey back; female with red mantleand sometimes with black crown, white sidesof head (including ear-coverts and subocu-lar feathers). Under-parts white with dark vermiculation in centre of chest and withoutobvious markings or grey streaking on sides.Greater under wing-coverts boldy darkbarred.


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DISTINCTIVE FEATURES DARK MORPHThe upper-parts are as in the previously described plumages and are only mentioned in passing here.

Age B. polyosoma 66,231 mm

1 year basic

Variable. Uniform bituminous to darkbrown with ochre markings on upper-parts, which are more abundant and warmer-coloured in females. Black-brown with pale spots on central under-parts and sides. Uniform underwing

with a few pale spots. Males with fewermarkings, darker more uniform thanfemale.

Similar underneath to juvenile B. albicauda-tus, with brown stripes on buff-tawny to rus-ty-ginger ground colour (blackish markingson white background in albicaudatus ). Brownand sometimes blackish barring on buffbackground on sides of head and neck; broadbrown-black malar stripe descend to sides ofchest. Central underparts dark brown withpale markings that give reticulated appearan-ce. Tighs and under tail-coverts with thickdark and pale barring. Under wing-coverts with profuse pale markings.

2nd calendar year

Variable. Brown to black-brownappearance, sometimes with varyingdegree of pale markings on the flanksand wing-coverts. Males at least seemfairly uniform, whilst females are moreprofusely marked.

Variable. Whole head blackish with striatedappearance; neck and chest uniform brown with visible black feather shafts. Centre ofchest blackish with feathers with pale emar-ginations, giving scale-like appearance; therest of the under-parts and thighs barred in

dark brown to cinnamon-ochre.

Immature

Variable. Head and bib uniform brown;central under-parts red-brown in maleor red in female, usually without ba-rring. Female with large dorsal patch.

Variable. Head and bib brown to grey-brown;males with red-brown chest and the rest ofthe under-parts brown with faint barring onlower under-parts; female with extensive redon under-parts with pale-bordered feathersand lower under-parts and thighs with paleor dark barring that reaches belly and blendsinto chest. Under wing-coverts whitish withdark barring.

Pre-definitive

Variable. Under-parts differ betweensexes: males almost completely lead- toblue-grey with red feathers mixed inthe mantle and centre of chest; female with grey head and extensive red areason under-parts, with black sooty areasabove all on sides, thighs and belly.

Variable. Males with bicolour reddish andgrey on lower hindneck and upper mantle;head and bib greyish , centre of chest as far asbelly reddish and the rest of the under-partsgrey, with quite dense barring. Te barringblends into the sides of the neck where itmixes in with the red pectoral band. Femalessimilar, but with extensive dorsal patch andcentral under-parts reddish, and lower under-parts with white and grey barring. Under andupper tail coverts white.


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a peculiar way (Walker, 2002, Cabot et al .,in this volume). It has the silhouette of aneagle, with a greater wingspan, and wings wi-der at the base (rounded at the back), and thetail proportionately shorter and rounder (fanshaped) than B. polyosoma. Te latter is sma-ller in size, more graceful, with a rectilinearoutline, narrow wings and a proportionately

longer tail. When perched, B. poecilochrous is more

voluminous, with long, large secondaries lea- ving the distal extremities of the primaries very little exposed. Te svelter Buteo polyo-soma appears to have proportionately longertarsals, especially those from the coastal de-sert of Peru and Ecuador.

In both species the wing tips overlap thetail in adults; this is from observation of cap-tive birds and in the field. However, this cri-terion should not be used, since it does not

serve to distinguish the species. Juvenilessuffer from a notorious shortening of the tailon becoming subadults, especially in B. poeci-lochrous. Notable shortenings also occur inB. albicaudatus and in G. melanoleucus wherethey even change morphology.

Recognition by measurement

Te following is a key to distinguish thespecies; measurements are expressed in mi-llimeters:

Measurements above those indicatedapply to B. poecilochrous and vice versa for B. polyosoma.

Over 1300 mm wingspan.Distance from the tip of the eighthprimary (P8) to the tip of P6 less than8mm. Wing width at centre (with the wings

spread) less than 260 mm.Distal width from P8 to the start of thedovetail more than 20 mm.Distal width from P9 to the start of thedovetail more than 23 mm.Distal width from P10 to the start of thedovetail more than 25 mm. Wing length measurements less than380 mm are characteristic of B. polyoso-ma males; length measurements over 445mm apply to B. poecilochrous females.

ACKNOWLEDGEMENS.– o Juan José

Negro for his valuable comments. o the curatorsof the various collections for allowing us to usetheir facilities to examine specimens: Doctor Jo-sefina Barreiro, bird curator, National Museumof Natural Sciences, Madrid; Doctor Sonia San-doval, Executive Director, Ecuadorian Museumof Natural Sciences; Doctor Marta Espinosa,Director, “Mejia” Museum of Natural Sciences,Quito; and Doctor Cristina Leon, Director, “Bo-livar” echnical Institute Museum, Ambato; Doc-

Definitive

Variable. Usually no barring on chestand belly, rump and uppertail covertsgrey. Sexes different underneath: maleall uniform lead-grey above and below;female back like male, but with dorsalpatch and red pectoral band, and withbelly and thighs sooty black, and withunder tail-coverts whiteish with sootyspots. Females from the FalklandsIslands have barred lower under-parts, while some from the Central Valleyof Chiles have fine pale barring in themiddle of the chest and pale markingson the under wing-coverts.

Variable. Usually obvious barring on centreof chest and belly. Under-parts similar inboth sexes. Chin and throat grey or white,black streaked, bib grey with white markings;centre of chest, thighs, belly and under wing-coverts with grey and white barring. Underand upper tail-coverts white. Some malesare more uniform in appearance and lackmarkings on mid and upper under-parts, buthave fine barring on flanks, thighs and belly.


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tor Gerhard Aubrecht, Landes Museum, Linz;Doctor Alice Cibois and Doctor Manuel Ruedi,Museum d’Histoire Naturelle Ville de Geneve,Geneva; Doctor Geraldine Veron, Museum Na-tional d’Histoire Naturelle, Paris; Dr H. BaagoeZoological Museum University of Copenhagen.Doctor Göran Frisk, Museum of Natural His-tory, Stockholm, Doctor René W. R. J. Dekker,Naturalis Leiden, Doctor Kees Roselaar and Miss ineke Prins, Zoological Museum Amsterdam,Doctor Lenglet, Institut Royal des Sciences Na-turelles de Belgique, Brussels; and Doctor Claudio

Pulcher, Museo Regionale di Scienze Naturali de urín; Dr Martin Päckert, Senckenberg NaturalHistory Collections, Dreden; Dr Sylke Frahnertof the Museum für Naturkunde, Berlin, and Dr erry Chesser at the US National Museum ofNatural History, Washington DC, for providingphotographs of specimens. We thank the staff ofthe British Museum of Natural History (in ring)for their outstanding attention during our visit totheir collection. o Fernando Hiraldo Cano, di-rector of the Estación Biológica de Doñana fortheir support. Also to María Angeles Prieto, Fer-

nando Feás Costilla and Javier Ceballos for theirinestimable help. We are most grateful to TereseNewenham for translating the conference presen-ted at the First Ecuadorian Ornitological Mee-ting, Quito, March 2005 (I Reunión Ecuatorianade Ornitología).

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Figure 1. Age related changes for B. polyosoma dark morph male


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Figure 2. Age related changes for B. polyosoma dark morph female


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Figure 3. Age related changes for B. poecilochrous dark morph male


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Figure 4. Age related changes for B. poecilochrous dark morph female

buteo polyosoma y buteo poecilochrous

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