An investigation into the hunting and home range of Verreaux’s Eagle Aquila verreauxii at Watler Sisulu National Botanical Gardens, Roodepoort.

INTRODUCTION

Verreaux’s Eagle Aquila verreauxii has a distribution close to that of rock hyraxes Procavia capensis and is thus 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). Monogamous pair bonds likely last for years and within a defended territory up to five nest sites may be used, although one is favoured (Simmons 2005). Bonded pairs remain close together in a day (75-95%) and will often hunt together.
Walter Sisulu National Botanical Gardens, Roodepoort, has been territory to a pair of Verreaux’s Eagle for many years; observations in the last 16 yrs (1993-2005) indicate that of 15 breeding attempts (no laying in one year) 11 successful fledgings occurred (L. Woodcock pers. comm.). None of these juveniles were marked or tracked so no details concerning post-fledging survival are known.
The Johannesburg greater metropolitan area is the largest urbanised region in South Africa. It is not known whether the home-range of the pair presently breeding in the Walter Sisulu National Botanical Gardens 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 returned prey to the nest site in breeding years suggest that habitat and hunting grounds have indeed become reduced in recent years. Presently the pair is supplemented with food since hunting success has 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.

OBJECTIVES

This study will seek to address and answer two major questions:

1. What is the hunting and home range of the Verreaux’s Eagle pair at Roodepoort?
By understanding the movement patterns and hunting range of Verreaux’s Eagles in a region of heavy urbanisation, we will seek to establish the long-term survival prospects for a Verreaux’s Eagle pair in a semi-urban environment.

2. What is the post-fledglings survival rate and how far do juveniles wander from the natal area subsequent to fledging?
Data on the survival of fledglings Verreaux’s Eagles are few; in addition nothing is known of the survival and dispersal of fledglings from the breeding pair at Roodepoort. Such questions are important in management decisions and maintaining the long-term persistence of this pair in the region.

Answering both questions will be important in assessing food supplementation protocols presently in place, where the pair are only supplied fresh prey after thorough observations on an 'as and when needed basis'

We will attempt to address these questions by applying the following techniques:

1. We will, through the use of GPS and cell phone technology, seek to determine the hunting range of one of the pair presently occupying the territory at Roodepoort. Since the pair often hunt together, data on the pairs movements will be obtained from tracking one individual. We will capture one of the pair and attach a backpack to the bird to monitor its movements (details of procedure and technology used follows below). This component of the project will be short term, and if data collection successful, applied in subsequent years to nestlings shortly before fledging. There is then scope to apply the technique to Verreaux’s Eagles country-wide. This technology will also allow us to establish movement patterns in time and space over a short-term period (see Appendix).

2. In successful breeding years nestlings will be ringed with a colour ring and Safring metal ring (G-ring; 26mm Incoloy). This component of the project will be long-term since it will rely on sightings being reported or the reporting of recovered rings or recaptured birds. When fitted with a backpack the adult will be fitted with the above described rings. Colour rings will also facilitate identification during observations in the area. Presently many dedicated observers are unable to sex the pair at the nest. Reports on prey returned by the eagles to the nest or gardens have reduced academic value and management decision making processes are thus less informative.

This project will form part of a broader project investigating the movement of rehabilitated vulture at de Wildt Vulture Unit. As such, the relevant expertise is on hand to assist with important components of the project (details of project participants to follow)..

Capture, backpack attachment and data analysis protocol are covered below.

METHODS

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 Pretoria (Academic advisor and project co-ordination)
Libby Woodcock - Black Eagle Project Roodekrans (Walter Sisulu National Botanical Gardens liaison, public relations and fund raising)
Kerri Wolter - De Wildt Vulture Unit (Harness application)
Dirk van Stuyvenberg, Ernst Retief, Rihann Geyser - Pretoria Bird Ringing Club (Bird Capture)
Paul Bartels – Pretoria Zoological Gardens (Advisory and field veterinarian, on site during backpack fitting)

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)
Andre Botha (Birds of Prey Working Group; Johannesburg)
Ben Hoffman (Africa Calling – Raptor Breeding and Rehabilitation Centre; Pietermaritzburg)

RISK ASSESSMENT AND PROTOCOL

The high profile of the Verreaux’s Eagles at Watler Sisulu National Botanical Gardens is recognised. As such, all necessary precautions will be made in ensuring the welfare and well being of the Verreaux’s Eagles involved in the project.

1. Bird capture and backpack fitting

This component of the project is being led by members of the Gauteng North Bird Ringing Club (Pretoria) and incorporates members with significant experience in bird ringing, and particularly experience in raptor capture and ringing. Members of the capture team are qualified A-permit ringers (Safring) and have a successful record of handling and ringing numerous raptor species (Appendix 2). Although many of these species are significantly smaller than those captured and ringed the process of handling birds remains the same.

1.1 Eagle capture and procedures

Capture of the Verreaux’s Eagle will occur using a Bal-chatri trap, a successfully proven technique used in the capture of raptors (Maritz XXXX). The successful use of this technique requires the application of strict protocol, e.g. the use of strong nylon gut with free running nooses. The cage will be designed with no sharp edges and weldmesh of suitable mesh size to ensure the safety of the bait. The trap will weigh c. 3kg with an attached weight of c. 1kg to allow limited movement of the trap. (A trap of excessive weight can cause damage to a captured bird when the bird attempts to fly off and resistance is a dead weight). A live rabbit will be provided as bait in the Bal-chatri and trap setting will occur in the early morning or late-afternoon to ensure reduced heat stress on the rabbit.
The capture team will remain in a position where they can view the trap, so that any response by the eagles is acted upon immediately. This will reduce the time that a captured bird is left on a trap, time that may prove detrimental to the health of the bird. On approaching the bird it will be covered in darkness by a towel; this prevents the bird from struggling so it can be removed safely from the trap. The nooses will simply be cut to reduced the time the bird is handled.
Once captured, the bird will be fitted with a calico bag over the head. This technique is similar to that used by falconers where the bird is placed in darkness to reduce panic whilst being handled. Also, it prevents biting and damage to itself and handlers. The talons will be isolated and held by one handler; to allow those working on attaching the backpack to work unhindered and prevent damage to handlers. If handled on the ground a towel will be used to reduce damage to the feathers of the bird.
First the rings will be fitted and then the backpack team will fit the backpack. A veterinarian (Dr Paul Bartels) will be on site to assure the procedure runs smoothly, and to attend to any health problems that the bird may encounter. The vet will also do a routine health check to ensure the bird is in good health before release. A blood sample will also be collected to test for possible diseases and poison loads obtained through feeding on poisoned prey in an urban environment e.g. rats, pigeons.

1.3 Backpack
Current consensus agrees that tracking devices attached to birds do not exceed 10% of the birds body weight, preferably not above 7%, with low mass attachments encouraged to decrease negative effects on normal behavioural activities (REFS). Weights given for Verreaux’s Eagle, and percentage of body mass of 200g backpack, are as follows; Male: 3.0 - 4.2kg (6.7 – 4.8%), Female: 3.1 – 5.8 kg (6.5 – 3,4%) (Gargett 1990). These fit within acceptable and ethical limits for both sexes.

1.3.1 The technology being used,
Traditional VHF radio tracking, in use since 1963, has required the tracking of animals to determine positions. This technique revolutionised wildlife research and has, since its inception, provided scientists and wildlife management with invaluable data on animal (individual and group) movements and behaviours. This form of research requires a level of intrusiveness that may affect results. Also, it requires triangulated fixes to determine position, or the animal to be sighted. The use of GPS-cell phone technology allows for a reduction in man-power and increase in data collection. Presently, backpacks weigh 200g for a device that is capable of recording 1200 data points. Positions are almost immediate, relying on a delayed response that the SIM card requires to make communication with towers. These time delays can be corrected for. However, methods are presently being tested to obtain instantaneous positions, as well as obtaining speed records. In addition, altitude is also recorded. Data concerning flight height in relation to variables such as time of day can be obtained, thus providing valuable biological data on Verreaux’s Eagles.
Although GPS tracking involves intrusive techniques during the initial stages of capture, a monitoring device can be applied to an animal and data simply downloaded as required. There is also no added concern of the animal moving beyond the range of the receiver where important data are not collected. GPS tracking systems rely on reliable cell phone coverage. Therefore, as the backpack device is within range of cell phone reception towers then a fix can be obtained. If not then a fix will be obtained as soon as the device comes within range. In the semi-urban environment of this study it is envisaged that there will be few moments when coverage is not obtained. Also, recording of position can be set to record data points as required. Although a limited number of points can be downloaded efficiency can be maximised by optimising the use of download time and battery life. For example, recording of positions can be geo-referenced; if the bird moves out of a certain set boundary e.g. the boundary of the Botanical Gardens, then data collection will commence. This would reduce superfluous data collection of numerous points should the bird remain at a specific site e.g. the confines of the garden. These data collection criteria can be reset so long as the device is within cell phone coverage.
We will aim to recover the tracking device by applying a weaker link of thin cotton on the harness. This will ensure the eagles activity and behaviour are not intruded on in the long term.

1.3.2 Past/present projects and "laboratory" testing,
Methods of attaching a mock back-pack have proved successful on White-backed Vultures. At DeWildt Vulture Unit an aviary tested Lappet-faced Vulture successfully carried a 200g pack in a large flight aviary for 2 months before it was removed. The harness system in no way hindered movement of the vulture and no signs of abrasion or irritation were observed on the bird itself. Tests with a similar backpack will be tested of a captive, non-releasable Verreaux’s Eagle held in captivity at XXXX (Lorna Stanton pers. comm.).

MOTIVATION

The use of modern technology provides the ideal opportunity to obtain valuable biological data for management decisions. This project will apply the expertise and knowledge of a broad base of dedicated conservationists to ensure the long-term conservation of a unique species.

Comparison with other projects

A 167g backpack (c. 3-3,5%) (Piper 2005) has been successfully attached to a juvenile Bearded Vulture Gypaetus barbatus in Crete and successful fixings of movements obtained for an annual period (http://www.environmental-studies.de/projects/28/vulture-1.html). In this project conventional radio tracking of the chicks hatched in previous years revealed that young Bearded Vultures; remain in an area when food is available until they consume it, forage 12-15 km from roosting site, often follow Griffon Vultures that aggregate in large numbers over carcasses, and prefer to forage in regions with low adult density. However conventional radio tracking failed to provide information on the exact period of abandonment of the natal territory and the initiation of the long range movements of the birds. Also gaps in the routes followed proved difficult. Similarly, technology used in this project allows for the setting of data received
In the USA, The Raptor Center has successfully satellite tracked numerous raptor species. The transmitter's worn are similarly worn like a backpack, where nylon straps extend from the box, go under the wings and are sewn on at the breastplate with biodegradable thread. The thread disintegrates in about 18 months causing the backpack to fall off in time (http://www.herald-journal.com/archives/1998/stories/raptor.html).

REFERENCES

Gargett, V. 1990. The Black Eagle. Acorn Books and Russell Friedman, Johannesburg.
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) J.A. Harrison, D.G. Allan, L.L. Underhill, M. Herremans, A.J. Tree, V. Parker & C.J. Brown. BirdLife - South Africa, Johannesburg.
Maritz, A. The ethics of raptor ringing. Safring News
Mech, l.D. & Barber, M.D. 2002. A critique of wild-life radio tracking and its use in national parks. unpubl. report. The Raptor Centre. University of Minnesota, St. Paul, Minnesota.
Piper, S.E. 2005. Bearded Vulture Gypaetus barbatus. pp. 484-485. In: Hockey, P.A.R., Dean, W.R.J. and Ryan, P.G. (Eds). 2005 Roberts’ - Birds of Southern Africa. VIIth ed. The Trustees of the John Voelcker Bird Book Fund, Cape Town.
Simmons, R.E. 2005. Verreaux’s Eagle Aquila verreauxii. pp. 531-532. In: Hockey, P.A.R.,
Dean, W.R.J. and Ryan, P.G. (Eds). 2005 Roberts’ - Birds of Southern Africa. VIIth ed. The Trustees of the John Voelcker Bird Book Fund, Cape Town.

APPENDIX 1. Contact details for major project participants:
Craig Symes
Department of Zoology and Entomology
University of Pretoria
Tel: 012 4204872 (w)
Cell: 0720710179
E-mail: craig.symes@zoology.up.ac.za
Kerri Wolter
De Wildt Vulture Unit
De Wildt Cheetah & Wildlife Trust
Tel: 012 5041921 (w)
Fax: 012 5041556
Cell: 0828085113
E-mail: vulture@dewildt.org.zaLibby Woodcock
Black Eagle Project Roodekrans
Tel: 0 011 958-1320 / 0826677097
Cell: 0826677097
E-mail: verreaux@mweb.co.za Paul Bartels B.V.Sc
Dirk van Stuyvenberg
Tel: 012 5483547 (h); 012 3114410 (w)
Cell: 0828380037
E-mail: stuyvies@telkomsa.net

Ernst Retief
E-mail: efretief@absamail.co.za Rihann Geyser
E-mail: RihannG@nda.agric.za

Additional professional input.

Zephné Bernitz B.V.Sc (Pret)
P.O. Box 1276
Middelburg
Mpumalanga
1050 South Africa.
Tel & fax: 013 2451438 (h)
Tel & fax: 013 2826419 (w) 013 2435266
Cell: 0836322970
E-mail: bernitz@iafrica.com

Andre Botha
Birds of Prey Working Group
Johannesburg
Ben Hoffman
Africa Calling – Raptor Breeding and Rehabilitation Centre
Pietermaritzburg

APPENDIX 2. Members of the Verreaux’s Eagle capture team indicating level of experience through the number of raptors successfully ringed.
Total number of raptor species ringed Total raptors ringed
Dirk van Stuyvenberg
Ernst Retief
Rihann Geyser
Craig Symes 12
(African Goshawk, Blackshouldered Kite, Jackal Buzzard, Lanner Falcon, Longcrested Eagle, Steppe Buzzard, Yellowbilled Kite, Fish Eagle, Secretary Bird, Wood Owl, Barn Owl) 31