Notes from the field - The first harvest

by ZSL on

Following on from the last report, ZSL London Zoo keeper Claire McSweeney updates us on the first harvest of Mauritius kestrel eggs.

I’m standing in the kestrel hand-rearing room, looking around at all the ticking and whirring equipment and fussing like a mother hen trying to make sure everything is working as it should. In just a few minutes, I’ll be leaving for one of the MWF field stations on the east coast of Mauritius and when I return it will be with a portable incubator full of kestrel eggs!

Wooden nest box in the branches of a large tree, being checked by conservationist
Kestrel boxes are designed to allow field staff to quickly and easily check for eggs and chicks with minimal disturbance

With me on ‘team kestrel’ is one of the Mauritian staff at the aviaries, Virginie. Two days after I arrived in Mauritius we were both lucky enough to travel to the Ferney Valley field station where we spent the night, ready for egg harvesting the next morning. The field station is set on the edge of the Bambous mountain range and acts as the MWF field team’s base from which they monitor kestrel nest sites.  Early Wednesday morning, we set out to visit the kestrel nest boxes having gathered everything needed for harvesting. It was quite a bumpy ride along the tracks but it was very much worth being out in the hills as along the way we suddenly came upon a pair of adult kestrels having a dust bath on the side of the trail. I wasn’t quick enough with my camera, although to be honest I was so busy watching them I’m not sure if I even thought about it. 

Several eggs carefully packed in to an incubator
Eggs are carefully placed in a portable incubator to keep them at the correct temperature
The plan for the day was to harvest 20 eggs and the process involved locating the nest boxes which the field teams knew were active, climbing up into the tree and carefully removing the eggs. The aim of the project is to collect eggs from the east coast and use the hand-reared chicks to bolster the west coast kestrel population. Meanwhile, the east coast females will soon lay a second clutch of eggs which they will, hopefully, successfully rear in the wild. A slight hiccup with our portable incubator meant we had to head back to the aviaries with just 10 eggs from three nest boxes. We think the battery in the 4x4 just wasn’t up to the task of running such a power hungry piece of equipment.

When we arrived back, the eggs were transferred from the portable incubator into one of our primed and ready incubators in the kestrel room and allowed to settle for a few hours. Later in the day Virgine and I started to process the eggs. The first step was to give them a quick wash to ensure there weren’t any large amounts of contaminates on the shell; a very important process as the growing embryo is pretty defenceless against any invading bacteria. We went on to weigh each egg and also to measure the length and breadth. This data is important as it allows us to make a few decisions about how to manage the environment in the incubator to ensure the egg hatches. The final task in processing the eggs, and the most exciting by far, is to candle them. Candling is a process by which you shine a bright light through the egg and in most cases you can see whether or not the egg is fertile. Out of the 10, seven were fertile and one unfortunately was fertile but the embryo had died at an early stage of incubation. 

Rows of kestrel eggs  being incubated
Our first batch of fertile kestrel eggs in the incubator

The next day the field team had got the portable incubators back up and running and brought another 11 eggs from three clutches to the aviaries. Five of these were fertile and joined the other six to bring a total of 11 fertile eggs from the first harvesting period. The first eggs were due to hatch around the 22nd so our job until then was to settle in and wait, making sure everything was running smoothly and ready for the arrival of our first chicks. 

 

Mauritius kestrel recovery program
 

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