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

More documents

Recommendations

Info

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
Page 1: Cotinga 35Observations at a nest of

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

Create successful ePaper yourself

Delete template?

Save as template?