Research & Innovation 2015-16 - Page 122



Feature
Flight risk
The martial eagle project continues to make strides in determining the causes
driving the decline of Africa’s largest eagle in protected areas such as the
Kruger National Park.
Rowen van Eeden, a PhD student at the Percy
Fitzpatrick Institute of African Ornithology and his
supervisor, Dr Arjun Amar hypothesise that perhaps
the most important factor driving these declines is the
high mortality of juveniles beyond protected areas,
when they disperse in search of vacant territory.
The long-range dispersal of juveniles has now
been well established using GPS tracking devices,
confirming previous findings from re-sightings and
recoveries of ringed juveniles that revealed that
martial eagles often disperse far from their natal
site. The tracking data show that after leaving their
natal territory, young martial eagles traverse areas of
up to 6 500 square kilometres, and many immature
birds from Kruger spend more than half of their time
outside protected areas. Here they face a suite of
threats that could limit the pool of birds available to
recruit into the park.
Even more worrying, however, is the discovery that
at least some adult birds, which were assumed
to be more sedentary than immatures, also travel
considerable distances and frequently venture beyond
Kruger. Many of these mobile adults are presumably
‘floaters’, birds waiting for a territory to fall vacant.
For instance, one adult female ranged far into
Mozambique, where she was killed.
Sadly, this was not an isolated incident. In April 2016,
a 4.6-kilogram female martial eagle was fitted with
a GPS tag in Kruger Park. Her capture and
the attachment of the tracking device were
recorded by a film crew documenting the
study for a British television programme,
narrated by well-known TV presenter Steve
Backshall. A few weeks later, the bird ventured into
Mozambique, and shortly afterwards, her signal
stopped moving, 160 kilometres from where she
had been tagged.
Van Eeden and a colleague set off to the bird’s
last known location, in a remote corner of
Mozambique, currently in the midst of renewed civil
unrest. They battled through dense bushveld, in an
area with few roads. Eventually, an hour-long walk
into the bush led them to a small game trail, where
– after searching through the long grass – they
found the remains of the eagle. Its tail was sticking
up between two bushes, and its neck was trapped
117 UCT RESEARCH & INNOVATION 2015–16
in a snare that had probably been set to catch small
antelope. Most people in the small villages in the
area rely on cattle herding, subsistence farming and
hunting to survive.
The death of a second adult martial eagle from
Kruger in rural communities in Mozambique is cause
for grave concern, especially as only eight adults
have been tagged with GPS transmitters. Without
GPS tracking, this cause of mortality would go
undetected.
A healthy population relies on having adults available,
to occupy vacancies created by the deaths of breeding
birds or to challenge ageing territory holders. A large
number of non-breeding adults probably signals a
relatively stable population. We don’t know enough
about the population structure of martial eagles in
Kruger, but the unnatural deaths of adult floaters may
be even more important in terms of affecting population
dynamics than the mortality of immature birds.
The findings confirm that even the largest protected
areas may be insufficient to conserve wide-ranging
predators; and that conservation efforts to safeguard
them are needed beyond park boundaries.
By the Percy FitzPatrick Institute of African
Ornithology, originally published in African Birdlife.
Image by Bernard Dupont, Wikimedia Commons.

African BirdlifeWikimedia Commons





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