Wednesday, February 4, 2015

Tagging and Testing. Summary 2015

As part of the research on the local population of eagles all nests are accessed to put id rings on the nestlings.  For ‘Angazi’ at Victoria Country Club, this day came on the 6th of January.

It is quite a technical process. Climbing involves attaching a fixed rope over a solid fork above the nest, and scaling the rope.  Armour must be worn as the adult crowned eagle, especially the female, is notoriously known to defend its young chick by striking the intruder with its talons.  Protection includes a foam-filled backpack and a riot helmet with false eyes painted on the rear – the adult eagles prefer to strike from behind as to take its target by surprise.

Preparing to climb the rope - note the lack of heavy armor.  Photo credit Kate Beer

This year I was attacked for the first time - a nest in Southbroom! Photo credit Kate Beer

afterwards at a nest in Pennington... more suitably attired.  Photo credit Claude Leroy


As they are already 2 to 3 kg and sporting fairly adept talons, the nestling must be sent to the ground to be ‘processed’.  This involves attaching the ID rings, taking measurements, and a small blood sample.  These nest visits are carefully timed to arrive at 65-75 days old.  The nestling is skeletally developed and therefore the rings fit nicely, while the flight feathers are still developing and the chick doesn't mentally think it can fly.

Upon reaching the nest , most often the nestling goes catatonic with fright.  A minority of nestlings will bravely face the intruder and flap its wings, bracing itself with its tail it wields those feet and talons to fend off any attacks.  On just two occasions in the last three seasons (2 of 58 nestlings ringed) have I had the horrific feeling of watching a chick bail from the nest.  Fortunately both of those chicks landed in vines and were retrieved without injury.  It is a real risk that fills me with dread every climb.  Each climb is carefully planned so as to get to the nest from below quietly and quickly – read to grab an active chick before it has a chance to think of options.  Placing a hand on the nestlings back usually allows me my first sigh of relief.  A hood is then fitted and the chick can be moved into its transport bag.

After hooding, the chick is placed into the transport bag.  Photo credit Leon Heyes

...and slowly descends to the ground.  Photo credit Leon Heyes


All of the 2012 and 2013 eagles were ringed with yellow tags.  This year 21 eagle nestlings have been ringed with new red rings.  There is just one last nestling to ring in early February, while in 2015 another 10 have been raised in inaccessible nest tree’s (typically old rotten ring-barked gum trees, or otherwise nests perched in precarious or unstable locations).  It is hoped that, once fledged, these young can also be caught and ID ringed.

Once on the ground at the base of the nest tree processing usually takes anywhere from 30-45 minutes.  After attaching the rings, a single drop of blood is collected from a small prick in the chicks toe.  From this drop of blood we take two different samples; which includes an Avian Sexing test and a genetic marker test.  Sandy Willows-Munroe at UKZN’s Biogenetic department will be taking the genetic sample and using various methods to test for the genetic diversity and relatedness of the individuals in the population – thereby making predictions about the dynamics and health of the population.  Meanwhile, the Avian Sex test is sent to the Molecular Diagnostic Services lab in Durban, the results telling us irrefutably what sex each eagle is.  Among raptors, females are larger than males and most researchers will use measurements such as head length and mass to estimate the sex.  We collect a number of measurements along with the blood sample thereby creating a reference set for future researchers.

Hooded, the chick sits quietly while we prepare the equipment. Photo credit Tim van der Meer

This years red rings are affixed with rivets. Photo credit Tim van der Meer

just a little prick.  Photo credit Claude Leroy

The nestling is suitably restrained for the blood sample.  Photo credit Tim van der Meer


After processing I can then climb the nest and haul the transport bag up to the nest.  All set up to descend, I finally remove the hood and the chick has but a glimpse of me descending below the rim of the nest. I can then breath another, much fuller, sigh of relief!  From all our experience with crowned eagles the one to two hours of handling and disturbance has no impact on the parents care and attention to the chick – just an hour or so afterwards life returns to normal at the nest.

And so, having mostly finished the 2015 season, the Avian Sex test results just came back to tell us that our “angazi” is a Mister.  Moreover, of the 21 nestlings of 2015 we have a really balanced demographic of 11 females and 10 males.

The hood is removed and the chick see's the climber descending.  Photo credit Leon Heyes


The results are in!


1 comment:

  1. Nice write-up Shane. Credit to the photographers. Thanks for sharing.

    ReplyDelete