Observations at a nest of Crested Eagle Morphnus guianensis in the ...

Cotinga 35Observations at a nest ofCrested Eagle Morphnusguianensis in the southern GranSabana, VenezuelaCrested Eagle Morphnusguianensis is a low-density, NearThreatened, resident of forestedareas of Middle and South Americathat is known in Venezuela fromthree specimens and a few otherrecords, most recently from thellanos in 2006 12 , from Junglaven,Amazonas, in December 2006 (G.M. Kirwan in litt. 2012), and fiveobservations by AC in the region ofEl Paují, Bolívar, since June 2008 2 .The latter involved both pale- andbarred-phase birds. AC has alsoseen Harpy Eagle Harpia harpyjatwice nearby 2 (c.1 and 3 km fromthe Crested Eagle sightings). Thisand a report by G. M. Kirwan (inlitt. 2012) of nests of both speciesseen in the early 2000s within1 km of each other in the Serrados Carajás, Pará, Brazil, provideadditional evidence of theirsympatry 5,11 , although Thiollayobserved that their territories didnot overlap in two study areasin French Guiana 9 . Nesting inVenezuela, in 1981, was reportedin Hilty 6 , and there are breedingdata for Brazil (north of Manaus)in 1984 1 , for Guatemala in 1995 10and Peru in 2002 7 .On 1 April 2011, we heardseveral long, high-pitched,unfamiliar whistles emanatingfrom forest canopy close to theEl Paují–Santa Elena dirt roadin the southern Gran Sabana,Bolívar, near a ridge in the ríoSurucún basin (in the headwatersof the río Caroní). On searching,we discovered a pair of CrestedEagles, close to a very large nest inthe main fork, at canopy level, ofan emergent tree. Annual rainfall 3in this region is 2,000–2,250 mmand the Surucún supports largelyintact primary forest of c.400 km 2 .The nest site is on a gentle slope,c.20 m lower and 220 m from theridge at 990 m elevation, alongwhich is the road carrying 30–60vehicles per day. A logging trailpasses below the nest tree andhas been used recently. To avoiddrawing the attention of huntersto the nest and because detailedbreeding data are available 1,10 , weShort CommunicationsFigure 1. Female Crested Eagle Morphnus guianensis, 30 June 2011; note white crestfeathers tipped black, and absence of barbules basally on the main crest feather; tailbarring is pale greyish brown above and white below (Anthony Crease)Figure 2. Female Crested Eagle Morphnus guianensis on nest, 30 June 2011(Anthony Crease)elected to sporadically monitor thenest from the ground, despite theinherent limitations. We openeda separate path to our mainobservation location and did notmeet anyone during our visits tothe nest, thereby fulfilling one ofour principal objectives, to avoidjeopardising the breeding attempt.The nest tree, a Baliziapedicellaris (Fabaceae), hascompound leaves mostly at itsextremities, so that the treeis open with unusually ‘clean’branches, providing easy accessfor a large raptor, and is a well-litlocation. The trunk, of 1.05-mdiameter near ground level, risesvertically to the primary fork c.23m above ground, where the nest islocated. Here, the tree separatesinto several large, widely spread,crooked branches, with upperfoliage 12–15 m above the nest.90

Cotinga 35Figure 3. Unfledged young Crested Eagle Morphnus guianensis, c.105 days of age, 30August 2011 (Anthony Crease)Figure 4. Juvenile Crested Eagle Morphnus guianensis in nest tree post-fledging, c.133days old, 27 September 2007 (Anthony Crease)Most trees around the nest havecrowns below c.24 m with a moreopen area and lower growth c.70m to the north-west, and an oldtreefall c.40 m to the south. Thenest is higher than most adjacenttrees, particularly those downslopethereby providing a wide view overthe canopy to the north, whichdirection was normally used by theeagles for take-off. The nest wasc.1 m in diameter, 0.8 m deep, andcomprised sticks up to c.3 cm indiameter, with lianas growing onthe sides, possibly originating fromleafy lianas brought by the eagles(Fig. 2). Such ‘adorning’ of the nestwith greenery has been reportedpreviously 1 .We visited the nest on 22occasions between 1 April and 1November 2011, for a total of 70hours, including some day-longvisits. We were unable to preciselydetermine the dates of laying andhatching. However, we did observeShort Communicationsthe young eagle’s first flightsand could therefore estimate thehatching date as 17 May, basedon 114 days to fledging 10 . Bycomparing our own observationswith 11 developmental milestonesprovided by Whitacre et al. 10 ,we can confirm 17 May as a fairestimate of hatching date. Layingand commencement of broodingoccurred between 1 and 15 April,consistent with the incubationperiod of 40–50 days assumed byBierregaard 1 .We first saw the young eagleon 30 June, at c.44 days of age (itwas not seen on days 10, 13, 21and 28). On 30 June the femalewas away from the nest for 80%of the day, including a periodof 30 minutes of light rainfall.In lowland Guatemala 10 , thefemale only left the young aloneat 59 days. It is probable thatthis difference reflects the coolerclimate (and considerably higherelevation) of our site, relieving thefemale of the need to shade theyoung earlier in its development.Development of the young andadult behaviour was otherwisesimilar to those in lowlandGuatemala, with two exceptions.Firstly, the young appeared lessexcitable (e.g., less jumping duringwing exercising and less reactionto over-flying vultures and otherlarge birds) and secondly, andmore significantly, we observedthe female withhold food fromthe young for many hours, duringconsecutive full-day visits 81and 99 days after estimatedhatching, which behaviour has notpreviously been reported in theliterature.At 81 days, the female left thenest area at 06h12, was seensoaring overhead at 10h30 andreturned to the nest at 11h08,remaining in the environswithout a break of more than 15minutes until 14h13. Additionally,during this period, the youngmade begging whistles almostconstantly, again implying theadult’s continuous presence. At13h16 the female was seen with aWoolly Mouse Opossum Micoureusdemerarae, presumably capturedduring the period of absence priorto 11h08. However, the prey was91

Cotinga 35Short Communications5. Normal whistles of adults; note slightly lower pitched 6. Long double whistle7. Long single whistle of femalewhistle of a second distant eagle at boom rightof femalewith short introductory notesBegging whistleof eaglet at 28 daysHigh-pitched, short doublewhistleof female, weeyuh8. Begging whistle 9. Whistles of eaglet aer fledging (133 days);of eaglet at 81 days ignore lower trace (insect)Figure 5 ‘Normal whistles’, three from one bird (probably the female), two from the other at slightly lower pitch.Figure 6. Long doubled whistle from female.Figure 7. Variant of female’s long whistle with introductory ‘squeal’, which is also commonly given alone.Figure 8. Begging whistle of young at 81 days.Figure 9. Whistles of post-fledged young at 133 days.All recordings made with EDIROL R-09HR and Sennheiser ME-67 microphone by Anthony Crease; software: Wavesurfer.not delivered to the young untilnearly 16h58. During this periodthe female landed and quicklytook off from the nest on sevenoccasions without depositingthe prey, despite the nestling’sbegging; and also whistledsporadically from nearby, causingthe pullus to redouble its beggingcalls. The eventual delivery justpermitted the young to feed beforedusk. Similar behaviour wasobserved 18 days later, when anunidentified large batrachian waswithheld for c.4 hours. Whateverthe reason for this behaviour,it appears that other factorsthan maximum weight gain,which would best be achieved byfeeding the young rapidly, arefunctioning.The female did not incubatethe egg or remain with the youngcontinuously, but took shortabsences when it was warm orthe nest was sunlit. However, shewas always present early in themorning prior to hatching andwhen the young was

Cotinga 35feather was devoid of barbs forc.30% of its length, perhaps dueto wear as it is pushed to and frobetween the shorter crest featherswhen rotating the head in windyconditions (Fig. 1). Loss of barbswas not observed in the juvenileat 19 weeks, supporting thehypothesis of wear as the causeof loss.Vocalisations comprise whistlesof variable length, separationand pitch pattern, and alwaysshow a second, and sometimesalso a faint third, harmonic. On1 April 2011, when both adultswere at the nest prior to laying,they uttered similar whistles(‘normal whistles’), of 1.0–1.4seconds duration, their pitch risingslightly to a peak of 2.7–3.0 kHz,then falling slightly, wiieeeuh(Fig. 5). In the sonogram, threeloud whistles by one bird andtwo fainter ones by the other atslightly lower pitch and longerspacing are visible. The louderwhistles are probably from thefemale, which appears strongervoiced, based on our cumulativeexperience. The female also madeloud and much longer (2.5–3.6seconds) whistles of similarpitch and pattern on 6 July 2011(Fig. 6). Whether this reflectedwarning or alarm is unclear.The whistles were mostly givendoubled with the second somewhatshorter (75%). A variant of thelong whistle was also recordedin which the pitch dropped veryslightly through 3 kHz and waspreceded by a short (0.38-seconds)high-pitched, bisyllabic squeal,skee’yuh (Fig. 7), which rises from4 to 6 kHz, before falling. Thissqueal was also commonly givenalone.Begging whistles of theyoung at 81 days are short (0.35seconds), see Fig. 8, and have acharacteristic pattern, which peaksearly at 5.5 kHz and then falls,rises and falls to c.4.5 kHz; tsiu.They are similar to those recordedat 50 days and appear to be anattempt to reproduce the adult’s‘squeal’. These begging whistleswere given in bouts of 3–10 with1–2 seconds between whistles. Aspreviously reported 10 , the youngappeared only to beg when theadults were in view or audible, andwas otherwise silent. At 19 daysafter fledging, the juvenile gavea different whistle (presumablynot begging as the adults wereabsent), similar in pattern to the‘normal’ whistles of adults, buthigher and shorter, twee (Fig. 9).AcknowledgementsWe thank Mario Gabaldónand Pierre Perret for helpingto identify the nest tree, RobBierregaard for his comments onthe submitted manuscript and GuyKirwan for many suggestions andimprovements to the same.References1. Bierregaard, R. O. (1984)Observations of the breedingof the Guiana Crested EagleMorphnus guianensis. WilsonBull. 96: 1–5.2. Crease, A. B. (2009) Avianrange extensions from thesouthern headwaters of therío Caroní, Gran Sabana,Bolívar, Venezuela. Cotinga31: 5–19.3. Corporación Venezolana deGuayana-Electrificacióndel Caroní (CVG-EDELCA)(2004) La cuenca del ríoCaroní: una visión en cifras.Caracas: CVG-EDELCA.4. Ferguson-Lees, J. & Christie,D. A. (2005) Raptors ofthe world. Princeton, NJ:Princeton University Press.5. Global Raptor InformationNetwork (2011) Speciesaccount: Crested EagleMorphnus guianensis. www.globalraptors.org (accessed 7July 2011).6. Hilty, S. L. (2003) Birds ofVenezuela. Princeton, NJ:Princeton University Press.Short Communications7. Raine, A. F. (2007) Breedingbird records from theTambopata-CandamoReserve Zone, Madre de Dios,south-east Peru. Cotinga 28:53–58.8. Restall, R., Rodner C. &Lentino, M. (2006) Birds ofnorthern South America.London, UK: ChristopherHelm.9. Thiollay, J. M. (1989) Arearequirements for theconservation of rain forestraptors and game birds inFrench Guiana. Conserv.Biol. 3: 128–137.10. Whitacre, D. F., Lopez Avila,J. & Lopez Avila, G. (2002)Behavioral and physicaldevelopment of a nestlingCrested Eagle Morphnusguianensis. J. Raptor Res.36: 77–81.11. Vargas-González, J. de J.,Mosquera, R. & Watson,M. (2006) Crested EagleMorphnus guianensis feedinga postfledged young HarpyEagle Harpia harpyja inPanama. Orn. Neotrop. 17:581–584.12. Vargas-González, J. de J., RiosUzcátegui, G. A., SerranoMarin, J. J., Cancion Arias,M. J. & Briceño David, E.J. (2010) Primer registro deÁguila Crestada Morphnusguianensis en los llanosoccidentales de Venezuela.Cotinga 32: 160–161.Anthony Crease andIvan TepedinoEl Pauji, Oficina de CorreosIpostel, Santa Elena de Uairén,Estado Bolívar, Venezuela.E-mails: trcrease@gmail.com andivantepui@yahoo.com.Received 1 November 2011; finalrevision accepted 31 July 2012;published online 10 March 201393