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Verreauxs’
Eagle Aquila verreauxii at the Walter Sisulu
National Botanical Garden, Roodepoort: Prospects for
their long-term persistence
Verreauxs’ Eagle Aquila verreauxii has a distribution
similar to that of the rock hyrax Procavia capensis
and is widespread in southern Africa, being absent from
the drier regions of the Kalahari, the plains of southern
Mozambique and north-eastern KwaZulu-Natal and mountainous
regions of Lesotho (Davies & Allan 1997; Simmons
2005). Populations are thus dictated by hyrax population
fluctuations, with breeding suppressed in years of low
hyrax numbers (Davies & Allan 1997).
Walter Sisulu National Botanical Garden, Roodepoort,
has been a territory for a pair of Verreauxs’
Eagle for many years. The breeding pair is of iconic
significance at the garden and they are a popular attraction
for tourists and visitors. Because of urban development
in the region, and resultant reduction in natural prey
items in the vicinity of the nest site, there is concern
over the persistence of these birds at the garden. Observations
over 16 years (1993-2005) indicate that of 15 breeding
attempts (no laying in one year) 11 successful fledgings
occurred (BEPR unpubl. data). This consistency in breeding
activity, with few irregularities, suggests that they
are unlikely to vacate the area. However, there is concern
that the effects of urban change in the region of the
garden may lead to future pressure for food resources
of breeding birds, and it is suggested that the pair
be strategically monitored to assess and monitor their
persistence at the garden.
It is not known whether the home range of the pair presently
breeding in the Walter Sisulu National Botanical Garden
at Roodepoort is marginal; and whether territorial hunting
grounds are impacted on by increased human disturbance
and development. Observations recording hunting success
and records of prey returned to the nest site in breeding
years suggest that habitat and hunting grounds have
indeed become reduced in recent years, resulting in
an increase in foraging range. Increased hunting distance
then has implications on long-term breeding prospects
and the viability of the territory in support a breeding
pair. Previously, the pair has been supplemented with
prey since hunting success is thought to have declined.
However, the pair has been successful in returning with
a variety of prey items. This prey diversification may,
however, be a response to reductions in preferable prey
items and it is suggested that prey diversification
has enhanced their survival at the garden. Supplementation,
however, was stopped in 2009 to investigate whether
the eagles would be able to sustain themselves and a
growing chick during their breeding cycle. Without feeding
fledging of the nestling was successful suggesting there
was sufficient food for the birds.
The breeding pair of Verreauxs’ Eagle at the Walter
Sisulu National Botanical Garden offers the ideal opportunity
to conduct research on the biology of an apex predator
breeding in an urbanised and human-altered environment.
Data collected on the biology of these birds are important
for our understanding of complex ecological interactions
present in our natural world. In addition, a greater
understanding and knowledge is important for management
decision-making processes, and the overall maintenance
of the integrity of the ecological functioning of the
garden. For many years volunteers have been involved
in the collection of breeding and feeding data of the
eagles. This has occurred on an ad hoc basis and has
contributed somewhat to our understanding the biology
of these birds. However, the value of observers has
been underutilised, mainly because of the inefficient
and misinformed manner in which data collection has
occurred. By refining observation and data collection
techniques we would like to propose a revision of the
overall research objectives of the Black Eagle Project
Roodekrans programme. This will involve a two tiered
research focus on data collection through, 1) observations
of breeding, feeding and behaviour, and 2) data collection
on the breeding biology of these birds through active
monitoring of the nestling each year. Each of these
points is elaborated on in more detail below.

OBJECTIVES
It is proposed to conduct research in three-yearly
intervals, with the intention of revising objectives
and aims as new information becomes available. The objectives
of the study during 2006-2008 have been revised and
are now indicated as follows. Specifically we will attempt
to address a number of overall questions that will contribute
to our understanding of Verreauxs’ Eagles in general
and in particular the current breeding pair at the garden.
1. What is the post-fledgling
survival rate and how far do juveniles disperse from
the natal area subsequent to fledging?
Data on the survival of fledgling Verreauxs’
Eagles are few; in addition very little is known of
the survival and dispersal of fledglings from the breeding
pair at Walter Sisulu National Botanical Garden or elsewhere.
No more than 400 Verreauxs’ Eagles have been ringed
in southern Africa (Oatley et al. 1998). Of those recovered,
most have been rehabilitated and/or relocated birds
(8 of 19), and few have survived longer than a year
(Oatley et al. 1998). This exemplifies the lack of knowledge
on this relatively common yet little known raptor species.
Answering these questions is important in management
decisions and maintaining the long-term persistence
of this pair in the region. With the input of numerous
raptor biologists, methods of tracking the fledgling
have been investigated.
1.1 GPS tracking
In 2007 a GPS backpack-tracking device, similar to
that used on vultures, was tested on an adult Verreauxs’
Eagle at the National Zoological Garden of South Africa
in Pretoria (Transponder ID 00-0020-2E53; Ring number:
G-18545). Fitting occurred on 26 March 2007 under the
supervision of Sarah Chabangu (Bird Curator) and Dr
Paul Bartels (expert veterinarian advisor). The device
was removed on 26 April 2007 with no apparent harm to
the bird. If successful, a similar device would then
have be attached to a wild nestling Verreauxs’
Eagle just before fledging. After much consideration,
despite the study on the zoo bird being successful,
it was decided not to attach a similar backpack to a
wild bird. It was felt that the device needed to be
significantly lighter. Efforts are therefore ongoing
in an attempt to source funding to attach a lighter
solar powered satellite transmitter to a wild bird.
Such devices now weigh approximately 1.5 g, are solar
powered and provide real time data on bird movements
(Kenward 2001). They have been used successfully for
tracking smaller species such as the Eurasian Hobby
Falco subbuteo (mass = c. 230 g; Strandberg et al. 2009)
to the Red-footed Falcon F. vespertinus Linnaeus 1766
(mass = c. 135g).
1.2 Patagial Tags
Patagial Tags have been used for a number of years
as a method for successfully tracking movements of vultures
(and other raptors) (Botha 2007). An advantage of this
technique is that a greater number of recoveries and
resightings are recorded (when compared to ringing),
providing valuable information on movements and vulture
biology. This technique will therefore be employed to
assist in monitoring the post-fledgling movements of
juveniles recruited every year at the Walter Sisulu
National Botanical Garden. In this instance, the fitting
of patagial tags will be supervised and carried out
by raptor biologists experienced in the process (e.g.
Andre Botha, Endangered Wildlife Trust). In addition,
we will draw on the expertise of researchers in Cape
Town (i.e. Lucia Rodrigues, Dr Andrew Jenkins) who have,
for the past few years, been successfully attaching
patagial tags to Verreauxs’ Eagle nestlings in
the Cape Town area (see Figure 1). This component of
the project will be long-term since it will rely on
re-sightings and the reporting of recovered rings or
recaptured birds. A wide network of amateur birding
enthusiasts in the field will record sightings. In addition,
the nestling will be fitted with a metal ring (Safring
G-ring; 26mm Incoloy) applied to the tarsus (tarsometatarsus).
The application of uniquely marked metal rings has been
applied for many years and is an ethically accepted
technique used in the study of birds (See http://www.birdingafrica.com/verreauxs_eagles.htm
for details of patagial tags on Verreauxs’ Eagle
in Cape Town).
The outcome of this aspect of the project will be the
accumulation of detailed data on the movements and post-fledgling
period of breeding Verreauxs’ Eagle at the WSNBG.

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Figure 1. (a) Patagial tags attached to nestling Verreauxs’
Eagle (Y005), before being returned to the nest, |
(b) fledgling resighted after leaving the nest showing ease
in identification (Y007) of the specific individual
(Photographs courtesy of Lucia Rodrigues). |
2. What are the effects
of urbanisation and development on the long-term prospects
for the persistence of breeding Verreauxs’ Eagle
at the Walter Sisulu National Botanical Garden?
This aspect of the project has been addressed by an
MSc student (see details below under Progress) and involved
summarising all feeding and breeding data collected
by volunteers of the BEPR. This report will be made
available on completion of the project.
1.1 Behavioural monitoring
of WSNBG Verreauxs’ Eagles.
Information collected to date by the volunteers of
the BEPR has been useful in understanding and monitoring
the breeding Verreauxs’ Eagle at the WSNBG. However,
for the information to be of sound scientific value
the methods of data collection need to be refined. Plans
are currently in progress to address this issue and
a standard format data sheet and training programme
with volunteers will occur in the near future.
This method of data collection has very little impact
in disturbing the eagles on the nest, if any. As a result
data collection will be ongoing. These data will be
valuable in interpreting data collected on bird activity
at the nest (i.e. interactions of parents with different
sex nestlings, diet of different sex nestlings, behaviour
of each parent towards different sex nestling etc).
METHODS
Nestling ringing will be carried out by an experienced
climber and bird-handler (Luke Verburgt). For the application
of the patagial tag the relevant expertise will be present
to apply the tag (see details of procedures above under
objectives; details of project participants to follow).
In addition, the project will operate through the input
of a number of experts in their respective fields; members
of the team being as follows (contact details of primary
project members given in Appendix 1 below);
Craig Symes - University of the Witwatersrand (Academic
advisor and project co-ordinator)
Libby Woodcock - Black Eagle Project Roodekrans (Walter
Sisulu National Botanical Garden liaison and project
co-ordination, public relations and fund raising)
Luke Verburgt – University of Pretoria (rock climbing
expertise)
Andre Botha – Endangered Wildlife Trust, Birds
of Prey Working Group (fitting of patagial tag)
Paul Bartels – Pretoria Zoological Gardens (Advisory
and field veterinarian).
Additional experts have been and will be consulted
further during the period of the project for additional
professional advice:
Zephné Bernitz (Veterinarian and southern African
raptor expert, Middelburg)
Ben Hoffman (Africa Calling – Raptor Breeding
and Rehabilitation Centre, Pietermaritzburg)
RISK ASSESSMENT AND PROTOCOL
The high profile of the Verreauxs’ Eagles at
Walter Sisulu National Botanical Garden is recognised.
As such, all necessary precautions will be made in ensuring
the welfare and well being of the Verreauxs’ Eagles
at the garden.
The senior member of the ringing team is a qualified
A-permit ringers (Safring) and has a successful record
of handling and ringing numerous raptor species. Someone
experienced in the process will conduct Patagial tag
fitment; i.e. Andre Botha who has a vast amount of experience
in fitting patagial tags to vultures.
Luke Verburgt is an experienced mountain climber and
member of the Mountain Club of South Africa. He has
experience in fitting vultures with rings and has during
2006-2008 accessed the nest at the WSNBG to fit the
nestling with a ring. In Cape Town nestlings have been
successfully removed from the nest for tagging before
being returned. This technique has proved successful
and no ill harm is received by the nestling. If a patagial
tag is to be attached to the nestling we would envisage
removing it from the nest for the process of attaching
the tag.
MOTIVATION
Progress to date:
During 2006-2008 the nestling was successfully ringed
at the garden. Information on breeding attempts in these
years are summarised below. Each of these nestling was
sexed, providing valuable long-term information on Verreauxs’
Eagle biology. Therefore, during the ringing and tagging
procedure efforts will be made to collect a small blood
sample (<50µl) for genetic sexing. This sample
will also be housed at the Wildlife Biological Resource
Centre - Biobank Africa (Director; Dr Paul Bartels).
Knowing the sex of each nestling will provide valuable
information on the breeding cycle of Verreauxs’
Eagle.
An MSc (coursework) student (Tamara Kruger) has recently
completed a project entitled, “Long term prospects
for the persistence of breeding Verreauxs’ Eagle
(Aquila verreauxii) at the Walter Sisulu National Botanical
Garden, Johannesburg”. This project investigates
habitat changes within the vicinity of the nest site
during the past three decades and summarizes breeding
and feeding data of the breeding pair at the garden
since 1993. This project is near completion and will
provide valuable information for future decision making
processes in the garden concerning the breeding Verreauxs’
Eagle. The outcome of this project will hopefully advise
on future data collection techniques concerning breeding
and feeding of Verreauxs’ Eagle at the garden.
Table 1. Verreauxs’
Eagle breeding data (2006-2008) (Libby Woodcock)
YEAR |
2006 |
2007 |
2008 |
| First egg laid |
11-Apr |
11-Apr |
11-Apr |
| Second egg laid |
16-Apr (5 days)
|
16-Apr (5 days)
|
15-Apr (4 days) |
| First egg hatched |
Didn't hatch |
26-May |
24-May |
| Second egg hatched |
31-May |
Didn't hatch |
27-May (3 days) |
| Abel died |
N/A |
N/A |
31-May (4 days) |
| Fledged |
7-Sep (99 days) |
2-Sep (98 days) |
2-Sep (96 days) |
| Left Territory |
17-Dec |
17-Nov |
- |
| Ring Dates |
15-Aug (76 days) |
20-Aug (84 days) |
6-Aug (76 days) |
| Ring leg |
right |
left |
right |
| Ring number |
G22031 |
G22032 |
G22033 |
| Sex |
male |
female |
female |
SUMMARY
The overall aim of this project is to engage with concerned
citizens on the wellbeing and persistence of Verreauxs’
Eagle at the Walter Sisulu National Botanical Garden,
Johannesburg. Through the co-ordinated efforts of scientists
and volunteers we hope to provide valuable information
on Verreauxs’ Eagles that will assist in long-term
decision making processes concerning development in
the immediate vicinity of the garden. This liaison will
engage all relevant stakeholders in formulating a working
strategy for the greater understanding of Verreauxs’
Eagles at the WSNBG.
Craig Symes
School of Animal, Plant and Environmental Sciences,
University of the Witwatersrand, e-mail: craig.symes@wits.ac.za
REFERENCES
Botha, A. 1007. A review of colour-marking techniques
used on vultures in southern Africa. Vulture News 56:
52-63.
Davies, R.A.G. & Allan, D.G. 1997. Black Eagle Aquila
verreauxii. Pp. 175-177. In: The atlas of southern African
birds
- Vol. 1.Non-passerines, (eds). Harrison, J.A., Allan,
D.G., Underhill, L.G., Herremans, M., Tree,
A.J., Parker, V. & Brown, C.J. BirdLife South Africa,
Johannesburg.
Kenward, R.E. 2001. A Manual of Wildlife Radio Tagging
(Biological Techniques). Academic Press, London
.
Oatley, T.B., Oschadleus, H.D., Navarro, R.A. and Underhill,
L.G. 1998. Review of ring recoveries of birds of prey
in
southern Africa: 1948-1998. Endangered Wildlife Trust,
Johannesburg.
Gargett, V. 1990. The Black Eagle. Acorn Books and Russell
Friedman, Johannesburg
.
Simmons, R.E. 2005. Verreaux’s Eagle Aquila verreauxii.
Pp. 531-532. In: Roberts’ - Birds of southern
Africa. 7th
edn. Hockey, P.A.R., Dean, W.R.J. and Ryan, P.G. (eds).
Trustees of the John Voelcker Bird Book Fund,
Cape Town.
Strandberg, R., Klaassen, R.H.G., Hake, M., Olofsson,
P. and Alerstam, T. 2009. Converging migration routes
of
Eurasian hobbies Falco subbuteo crossing the African
equatorial rain forest. Proc. R. Soc. B 276: 727- 733.
APPENDIX 1. Contact details for significant
research project participants.
Craig Symes PhD
School of Animal, Plant & Environmental Sciences
University of the Witwatersrand
Private Bag 3
WITS, 2050
Tel: 011 486 4700 (w)
Cell: 072 071 0179 |
Libby Woodcock
Black Eagle Project – Walter Sisulu Botanical
Garden
Tel: 011 7953622
Cell: 082 667 7097
E-mail: verreaux@mweb.co.za |
Kerri Wolter
Vulture Programme: Manager & Director P.O. Box
180
Krugersdorp, 1740
Cell: 082 808 5113
E-mail: kerri.wolter@gmail.com |
Paul Bartels B.V.Sc
WRBC (wildlife Biological Resource Centre)
DNA Bank
Tel: 012 305 5840 (w)
Cell: 082 990 3533
E-mail: paulb@wbrc.org.za |
Luke Verburgt MSc
Department of Zoology and Entomology
University of Pretoria
Pretoria, 0002
Tel: 012 420 4872 (w)
Cell: 084 842 7457
E-mail: lverburgt@zoology.up.ac.za |
André Botha
Manager: Birds of Prey Working Group
Endangered Wildlife Trust
Private Bag X11
Parkview, 2122
Tel: 011 486 1102 (w)
Cell: 082 962 5725
E-mail: andreb@ewt.org.za |
Additional professional input.
Zephné Bernitz B.V.Sc
P.O. Box 1276
Middelburg
Mpumalanga, 1050
Tel: 013 245 1438 (h); 013 282 6419 (w)
Cell: 083 632 2970
E-mail: bernitz@iafrica.com |
Ben Hoffman
Africa Calling – Raptor Breeding and Rehabilitation
Centre
Pietermaritzburg
Cell: 082 359 0900
E-mail: rescue@africanraptor.co.za |
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