86 SHORT NOTES Forktail 32 (2016)
The Critically Endangered Philippine Eagle Pithecophaga jeﬀeryi is
one of the world’s largest forest eagles and is known to occur only
on the Philippine islands of Luzon, Leyte, Samar and Mindanao
(BirdLife International 2016). Since its discover y (Ogilvie-Grant
1897), most studies pertaining to the biology of the species have
been focused on Mindanao. Exploration of Luzon has led to the
detection of adult eagle pairs and young birds; however, no active
nest has previously been found. Here we report the ﬁrst discovery
and observation of an active Philippine Eagle nest in 2015 and
record the nest characteristics, prey items and breeding biology of
the eagles on Luzon. We also report details of what we believe was
another Philippine Eagle nest found in 2013.
We searched for Philippine Eagles and their nests in the northern
Cordillera range of Calanasan, Apayao province, Luzon, during
intermittent expeditions between November 2011 and April 2015.
Our survey sites in the range consisted of predominantly secondary
dipterocarp and montane forests in mountainous terrain from
100 to 1,200 m. We divided the 2,592 km2 study area into a 5 km
× 5 km grid map, and systematically selected survey locations
based on local reports of eagle sightings and appropriate forested
Our ﬁrst success was on 22 March 2013 when we discovered a
large stick nest in the interior of montane forest in the northern
Cordillera range at 1,098 m. After making sure the nest was empty,
we climbed the tree—an almaciga Agathis philippinensis, similar
to some of the trees used by Philippine Eagles for nesting on
Mindanao—using ropes and harnesses. The nest was 1.02 m in
diameter and 0.73 m deep, and we judged that it was too big to
belong to a smaller Philippine raptor; we had already seen the nests
of, for example, North Philippine Hawk Eagle Nisaetus philippensis
in the same mountainous area, but this nest was signiﬁcantly larger
and we concluded that only Philippine Eagles would build a nest of
this size. We also found evidence that the nest had recently been
in use: twigs on the nest bowl appeared intact and fresh, whilst
foliage and epiphytes surrounding the nest appeared recently torn
and had not yet grown over it.
It appeared that the nest had been deliberately located so that
it was concealed by the epiphytes surrounding it. It is interesting
to note that we had seen a juvenile Philippine Eagle about
3.1 km from this nest-site about a week earlier. However, we have
no evidence linking this bird directly to this nest; although the nest
was empty, we monitored it for a few months but never saw either
juvenile or adult birds return to it.
We surveyed for eagles from vantage points on hilltops and in
the canopy of tall trees. When an eagle was detected, we made a
systematic ground search for potential nest trees using locations
from which they had emerged or where they descended into
the forest canopy. After a series of sightings that included a food
delivery by one of the adult eagles, we found the active nest on 21
April 2015 and observed it from 29 April to 1 September. The nest
was on a densely forested slope of lowland dipterocarp at about
450 m, built at a height of 31 m in the middle canopy of a 2.29 m
dbh Hopea sp. tree. The nest was surrounded by towering pandan
Freycinetia sp. epiphytes (in much the same way as the empty
nest found in 2013) and was substantially concealed by the thick
foliage of an adjacent Rauvolﬁa sp. tree (Plate 1). It was roughly
circular in shape, 1.54 m in diameter and 0.5 m deep. Based on the
development of nestlings on Mindanao (Kennedy 1977, Ibañez et
al. 2003, Ibañez 2007), we estimated the age of the chick to be over
one month when the nest was found. Hence the egg was probably
laid towards the end of January 2015 and hatched around the end
of March, indicating that the onset of breeding of Philippine Eagles
on Luzon was relatively delayed compared with those on Mindanao.
The 2015 nest site was about 31.45 km north of the disused
nest found in 2013, located within an area protected under the
‘Lapat’ system, an adaptation of traditional indigenous natural
resources management (Sadao 2010) by local government and
central government oﬃces working together (Local Government
Unit [LGU] Calanasan & Communit y Environment and Natural
Resources Oﬃce [CENRO] Calanasan 2011).
We recorded nest activit y at 10 minute intervals, and also
oppor tunistically recorded rarer events such as practice flights
and other noteworthy behaviour when they occurred outside this
sampling regime. We followed Marti et al. (1987) in computing the
biomass of the food items (quantity × weight) and their percentage
biomass (individual biomass/total biomass × 100). We also computed
the numerical percentage (number/total number × 100). The weights
of food items were based on the mean specimen weights published
by Kinnaird & O’Brien (2007) and FMNH (2010), plus data provided
by E. Sy and B. Santos (unpubl. data).
Philippine Eagles are sexually dimorphic, with females weighing
nearly a third more than males. Apart from their size diﬀerence,
the male and female adults were distinguished from each other
through features peculiar to each bird, such as relative size and
structure of tarsi, the presence of torn and moulted feathers, and
other plumage features.
Nest monitoring results
We monitored eagle activity at the nest and food deliveries to the
nest daily using a 20–56× spotting scope from a canopy observation
hide located about 60 m away. In total, we spent 977 daytime
hours over 92 days up to 1 September monitoring the nest and the
eagles’ activities. The main everyday activities (89.8%) of the chick
recorded from the nestling to the pre-ﬂedging stage were related
to general maintenance such as perching, sleeping, preening and
defecating (n = 5,267 individual records). Five percent of activities
involved feeding by the adults and feeding on its own (n = 294).
Other signiﬁcant activities included vocalising (3.6%, n = 210),
object play consisting of grabbing and biting at sprigs (1.3%, n =
75), and ﬂapping exercises (0.4%, n = 18), all of which became more
frequent as the chick grew; the chick’s developmental milestones
are given in Table 1. On 20 July, about two weeks before the nestling
began practice ﬂights, the opportunity arose to carefully trap it
for examination and to attach a ring and transmitter. Comparison
of its size and weight at that time with nestlings of a similar age
monitored on Mindanao indicated that it was a female.
We documented a total of 59 food items brou ght to the
nest, consisting of 12 vertebrate species. The two most common
were Northern Luzon Giant Cloud Rat Phloeomys pallidus and
Smooth-scaled Mountain Rat Snake Ptyas luzonensis. The cloud
rats were also the most important food item in terms of biomass
contribution. The rest of the food items were other rat snakes,
monitor lizards, macaques, civets and a ﬂying fox. There were
also portions of unidentiﬁed birds that we suspect were Northern
Rufous Hornbills Buceros hydrocorax and of unidentiﬁed rodents that
were most likely to be Philippine Forest Rats Rattus everetti. Many
items were already decapitated and dismembered so that they
First nesting record of Philippine Eagle Pithecophaga jeﬀeryi from Luzon,
Philippines, with notes on diet and breeding biology
TATIANA ROSE C. ABAÑO, DENNIS JOSEPH I. SALVADOR & JAYSON C. IBAÑEZ
Forktail 32 (2016) SHORT NOTES 87
could not be identiﬁed with certainty. In terms of biomass, mammals
(57.6%) made the largest contribution to the chick’s diet, but in terms
of the number of food items, reptiles made up 37.4%, mammals
32.3%, birds 10.2% and unidentiﬁable items 20.3% (Table 2).
Although we found no signiﬁcant diﬀerence in the placement of
the nests compared with those on Mindanao, where the mean
nest diameter is 2 m (Gonzales 1968, Kennedy 1985, Ibañez 2007),
the nests on Luzon were relatively smaller. This diﬀerence in size
and the atypical concealment of the nest by surrounding foliage
are probably adaptations to protect it from strong winds during
typhoons. The egg-laying time on Luzon appeared to be somewhat
delayed compared with the typical September–December egg-
laying season on Mindanao (Kennedy 1985, Ibañez 2007). This
delay is probably another adaptation to cope with the typhoon
season—typhoons occur about 80% more frequently on Luzon
than on Mindanao (PAGASA 2011) and aﬀect the region more
frequently in the period from July to December (PAGASA 2015).
Although, as reported in Table 1, we saw the juvenile ﬂying away
from the nest-tree to another tree 100 m away on 26 August 2015,
this was not the ﬁnal time that the juvenile made use of the nest:
she continued to return to the nest-tree and to be seen in the close
vicinity a number of times after that date. Based on our experience
of the behaviour of juvenile Philippine Eagles on Mindanao, we
would anticipate that she is likely to ﬁnally move away from this
area around the end of 2016. Likewise, the same hypothesis—
based on Mindanao breeding period observations that, following
an incubation period of about two months, a juvenile eagle will
mostly reside in or close to its birthplace for a period of around 21
months—may be applied to the young eagle seen in mid-March
2013. It was never seen again in the area close to the recently
vacated nest-site that we found on 22 March 2013, implying that if
it did originate there it was already on the move when we saw it. If
that was the case, its parents may have bred early in 2011 (around
January), similar to the 2015 Luzon pair.
Both the Luzon nests were located deep in forest interiors; this
is diﬀerent from Mindanao where the majority of nests are within
100 m of the fore st edge (Bue ser et al. 2003). However, whilst the
nest found in 2013 at 1,098 m was well within the known altitudinal
range on Mindanao—630–1,434 m (Ibañez 2007)—the 2015 nest
at about 450 m is about 200 m lower than previously reported on
Tab le 1. Summary of the dates on which indicators of the development
of the young Philippine Eagle in the Luzon nest were ﬁrst documented;
the estimated hatching date was the end of March 2015
Date Indicat ors of juvenil e development
1 May 2015 Object p lays; weak vocalisati ons; momentary up right posture; wal king with tiny steps
6 May 2015 Flapping exe rcises
9 May 2015 Feeding in dependently bu t with the adult fema le on the nest
24 Jun 2015 Feeding indep endently on lef tovers withou t an adult on the nest; i mproving uprig ht
posture, p erching and other a ctivities
26 Jun 2015 Feeding indep endently on fre sh prey delivered by t he adults
7 Aug 2015 Pr actising ight s out of the nest bow l and hopping and yin g from one branch to
another in th e canopy above
26 Aug 2015 Flight from nes t tree to another tr ee 100 m away
Table 2. Summary of the food items delivered by the adult Philippine
% of Weight Biomass
Food item No. total (kg) (kg) %
Unidentie d prey 12 20.3 – – –
Northe rn Luzon Giant Cloud R at Phloeomys pallidus 8 13.6 2.6 20.8 22.8
Smooth-s caled Mountain R at Snake Ptyas luzonensis 8 13.6 1.2 9.6 10.5
Unidentie d birds 6 10.2 1.8 10.8 11. 8
Philippin e Water Monitor Varanus marmora tus 6 10.2 1.2 7. 2 7.6
Reddish Rat S nake Coelognathus ery thrurus manillensis 5 8.5 0.3 1.5 1.9
Unidentie d rodents 4 6.8 0.5 2.0 2.1
Long-tail ed Macaque Macaca fascicul aris 3 5.1 6.5 19.5 21.3
Palm Civet Parado xurus hermaphroditus 2 3.3 3.0 6.0 6.6
Red-tail ed Green Rat Snake Gonyoso ma oxycephalum 2 3.3 0.3 0.6 0.8
Malayan Cive t Viverra tangalunga 1 1.7 4.0 4.0 4.4
Mottle -winged Flying Fo x Desmalopex leucopterus 1 1.7 0.4 0.4 0.4
Northern Sierra Madre Forest Monitor Varanu s bita tawa 1 1.7 9.0* 9.0 9. 8
Tota l 59 100.0 91.4 100.0
*based on o ne specimen only
Plate 1. Philippine Eagle Pithecophaga jeﬀeryi nest in the canopy of a
Hopea sp. tree, 11 May 2015.
TATIANA ROSE C. ABAÑO
Plate 2. Adult female eagle feeding young, 6 May 2015.
TATIANA ROSE C. ABAÑO
88 SHORT NOTES Forktail 32 (2016)
The Yellow-bellied Tit Pardal iparus venus tulus, classiﬁed as Least
Concern (BirdLife International 2015), is a species of forests and
woodlands previously thought to be endemic to south-east and
north-east China (Gosler & Clement 2016). Since 2011, a standardised
bird ringing programme has been carried out as part of the Amur
Bird Project at Muraviovka Park, Far East Russia (Heim & Smirenski
2013). The Muraviovka Park for Sustainable Land Use (49.874°N
127.704°E) is a non-government-managed nature reserve, about
50 km south-east of Blagoveshchensk, Amurskaya oblast (Heim
2016). It covers 6,500 ha of wetlands with small deciduous forest
islands, along the middle reaches of the Amur River.
On 25 September 2013 at 11h00, a juvenile Yellow-bellied Tit
was caught in a mist-net located in a deciduous grove close to farm
First record of Yellow-bellied Tit Pardaliparus venustulus in Russia suggests a
signiﬁcant range extension of a species formerly endemic to China
P. FETTING, S. THORN, M. PÄCKERT & W. HEIM
buildings (Plate 1). The following measurements were recorded:
wing length 63.5 mm, p8 length 48.0 mm, tarsus length 17.0 mm,
bill (to skull) 10.6 mm, fat score 2, muscle score 3, weight 11.0 g.
Body feathers were collected for genetic analyses. Body dimensions
matched the literature values for P. ve nu stu lu s: wing (of male) 61–68
mm, tarsus 14.2–18.0 mm, weight 9.0–12.5 g (Harrap & Quinn 1996).
Whilst this bird was being ringed, a pair of adult Yellow-bellied Tits
were photographed near the mist-net (Plates 2 & 3). The ringed bird
was recaptured (once) at 10h00 the following day.
The feather samples were used for genetic barcoding analysis
with the standard marker cytochrome-oxidase I (COI). DNA was
extracted using the sbeadex® forensic kit (LGC Genomics) according
to the manufacturer’s instructions. Standard bird primers and PCR
Our records of food deliveries to the Luzon nest also revealed
important diﬀerences between Luzon and Mindanao. In terms of
biomass contribution, the Northern Luzon Giant Cloud Rat was the
most important prey species on Luzon, unlike Mindanao where the
Long-tailed Macaques made up the highest biomass contribution
(36.5%). In numerical terms the Northern Luzon Giant Cloud Rat was
also one of the top prey species on Luzon, in place of the Philippine
Flying Lemur Cyno ce ph alu s v ol ans and Mindanao Flying Squirrel
Petinomys crinitus, the most numerous prey items on Mindanao
(Kennedy 1985, Ibañez et al. 2003, Ibañez 2007); these two species
are absent from Luzon. On Luzon, reptiles numerically accounted for
37.4% of the prey items, compared with less than 10% on Mindanao
(Kennedy 1985, Ibañez 2007), suggesting a greater variety of available
prey on Luzon. Finally, it is noteworthy that no domestic animals
were recorded from the Luzon nest, contrary to the observations of
Concepcion et al. (2006) and Ibañez (2007) on Mindanao.
The diﬀerences in both nest location (altitude and habitat)
and breeding period discovere d during the inves tigation of
this firs t confir me d bree di ng record on Luzon suggest that
some temporal and range adjustments may be needed in ongoing
nest search eﬀorts in the region. More signiﬁcantly, the noteworthy
location of the two nests so far discovered in pristine forest interiors,
as well as the apparent variety and suﬃciency of wild prey, together
strengthen the need to maintain and enhan ce existing local
conservation strategies for the area.
We dedicate this paper to the late Mayor Elias K. Bulut Sr. for his
political will to conserve Calanasan forests. San Roque Power
Corporation and the Phil. Tropical Forest Conservation Foundation,
Inc. funded our expeditions. We thank the local governments of
Calanasan and Apayao, the Department of Environment and Natural
Resources, A.M. Oxales III, P.S. Balicao, A.A. Allado, R.M. Masalay and
G.S. Opiso. We also thank E. Sy, B. Santos and A. Diesmos for reptile
prey identiﬁcation and biomass computation.
BirdLife International (2016) Species factsheet: Pi thecop haga jef feryi .
Downloaded from http://www.birdlife.org on 07/08/2016.
Bueser, G. L., Bueser, K. G., Afan, D. S., Salvador, D. I., Grier, J. W., Kennedy,
R. S. & Miranda, H. C. (2003) Distribution and nesting density of the
Philippine Eagle Pithecop haga jeﬀeryi on Mindanao Island, Philippines:
what do we know after 100 years? Ibis 145: 130–135.
Concepcion, C. C., Sulapas, M. & Ibañez, J. C. (2006) Notes on food habits
and breeding and nestling behavior of Philippine Eagles in Mount Apo
Natural Park, Mindanao, Philippines. Banwa 3: 81–95.
FMNH (Field Museum of Natural History) (2010) Synopsis of Philippine
mammals. Downloaded from http://archive.fieldmuseum.org/
philippine_mammals/ on 15/04/2016.
Gonzales, R. B. (1968) A study of the breeding biology and ecology of the
monkey-eating eagle. Silliman J. 15: 461–491.
Ibañez, J. C. (2007) Philippine Eagle Pithecophaga jefferyi breeding
biology, diet, behavior, nest characteristics and longevity estimate in
Mindanao Island. MSc Biology Thesis. Downloaded from https://www.
researchgate.net on 28/12/2015.
Ibañez, J. C., Miranda, H. C., Balaquit-Ibanez, G., Afan, D. & Kennedy, R. S.
(2003) Notes on the breeding behavior of a Philippine Eagle pair at
Mount Sinaka, Central Mindanao. Wilso n Bull. 115: 333–336.
Kennedy, R. S. (1977) Notes on the biology and populations status of the
Monkey-eating Eagle of the Philippines. Wilson Bu ll. 89: 1–20.
Kennedy, R. S. (1985) Conservation research of the Philippine Eagle. Nat.
Geogr. Soc. Res. Rep. 18: 401–414.
Kinnaird, M. F. & O’Brien, T. G. (2007) The ecolo gy and conservation of Asia n
hornbills: farmers of the f orest. Chicago: University of Chicago Press.
Local Governmen t Unit (LGU) Calanasan & Communit y Environment
and Natural Resources Oﬃce (CENRO) Calanasan (2011) Adoption of
indigenous cultural practices in implementing Executive Order No.
23: the Calanasan way.
Marti, C. D. (1987) Raptor food habit studies. In B. A. Giron-Pendleton, B.
A. Millsa., K. W. Cline & D. M. Bird, eds. Raptor manag ement technique
manual. Washington: Wildlife Federation.
Ogilvie-Grant, W. R. (1897) On the birds of the Philippine islands. Part IX.
The islands of Samar and Leite. Ibis (7)3: 209–250.
PAGASA (Philippine Atmospheric, Geophysical and Astronomical Ser vices
Administration) (2011) Climate change in the Philippines. Downloaded
from https://www.pagasa.dost.gov.ph on 22/08/2016.
PAGASA (Philippine Atmospheric, Geophysical and Astronomical Ser vices
Administration) (2015) Seasonal climate outlook. Downloaded from
https://www.pagasa.dost.gov.ph on 22/08/2016.
Sa da o, N. C. (2010 ) La pat sy stem: an indige nous n atur al res ource
management system of the Isnags in Apayao. Downloaded from http://
agris.fao.org/ on 13/10/2016.
Tatiana Rose C. ABAÑO & Dennis Joseph I. SALVADOR, Philippine
Eag le Foundati on, Ma lagos, Bagu io Distric t, Dava o City 8 000,
Philippines. Email: email@example.com (corresponding author)
Jayson C. IBAÑEZ, University of the Philippines Mindanao, Mintal,
Davao City 8022 and Philippine Eagle Foundation, Malagos, Baguio
District, Davao City 8000, Philippines.