With thanks

Another breeding season has come to an end for the Black eagles which gives me time to reflect on another season of research.

For the eagles it was certainly a tough year in the Cederberg – With only 11 pairs attempting to breed and only 6 young fledging. Must note here that since the helicopter survey there are of course many nests which are not included in these statistics. Nevertheless it certainly highlights the high rate of failure, mostly caused by adverse weather during the hatching stage.

In contrast I have had many happy adventures in the Sandveld this year and seen an incredible breeding success story there – of the 17 pairs monitored 13 fledged a young.

I’ve put together some data below, which Lucia Rodrigues and Cape Nature have also made contributions to. Overall the most surprising result for me has been the much higher successful breeding attempts in the Sandveld compared to the Cederberg. However, don’t take this on face value – the eagles occur more densely and with more inter-pair competition in the ‘berg. So perhaps if we represented the data as successful breeding per km² we’d see a slightly different story.

Figure 1: Breeding outcome of Black eagles from 2010-2012 (n=83) based on 39 nest sites.

So as this season closes I wanted to say a big thanks for all of your support, interest and encouragement – Special thanks to Quinton & Liz (Cape Leopard Trust), Driehoek Wine, K-Way, David & Cisca (Cederberg Cellars), Kevin (Darling Brew), Les Underhill & Andrew Jenkins (ADU), Cape Nature, Dickon (Evosat), Victor (Spanish Ministry of Environment), Hank, Alan, Marcus, Anzio (Eagle Encounters), Tom & Tessy (the Vlei), Patrick, Karen & Pierre (Waganpad), Tilia & Lawrence (Donkieskraal), Louise & Gary (Leipoldtville) and everyone I’ve met on the road!

See you all next season!

Nest surveys - by helicopter!

Last week the BEP teamed up with Base 4 Aviation to conduct the first ever aerial survey of the Cederberg cliffs for Black eagle nests. Excitement had been running high for the possibility of this survey since I received the first email from Stefan Fouche, a helicopter pilot and instructor in Cape Town; “I work for Base 4 Aviation - Helicopter charter company & flight school.  From our side, I want to expose our student pilots to as many area's, conditions, operational experience as possible.  To prepare them as well as possible for their career as pilots.  What I'd like to know is... how can we help you?  At no cost I might add.  Animal surveys, plant surveys?  The fantastic thing about a helicopter is time saved in moving people, the ability to see the bigger picture, finding people or animals etc.” It is not often you get given an opportunity like this so the whole team was elated when permits came through and finally the helicopters arrived in the Cederberg last week.

The plan was to fly along all cliffs with an observer onboard whose job it would be to spot, take a GPS location and photograph all nests. Timing is of the essence and scanning the cliffs constantly was the only way we could pick up on the new sites. The skill of the pilots was also key – mountain flying is unpredictable at the best of times so they were ever-ready to pull away from the mountains in a tricky situation or unexpected downdraft.

We spent three days in the air and covered more ground than I have managed to in the last two years on foot. In the Cederberg we found 35 previously unknown nest cliffs – which more than doubles what I had already located by hiking! We also took the opportunity to make a flight out to the Sandveld where we found an additional 11 nest sites. This data is an invaluable contribution to my research and will give us a greater understanding of the population size and distribution of eagles in this area.

A sample of the nests we found.

I am extremely grateful to Base 4 Aviation for their time, Driehoek Tourist Farm for a landing field and accommodating the team, Lucia Rodrigues & Patrick Banville for their dedication to finding the nests and Cape Nature for allowing this survey to happen – we all came away feeling highly privileged to have the opportunity to experience the beautiful Cederberg from a new perspective!

To share our experiences please check out the video which Stefan made from footage taken during the survey:

The Ups and Downs of research

This season has seen many highs and lows of field work. The moment in May this year when we GPS tagged the first ever wild Verreaux’s eagle will always be ranked as my personal high. I don’t think anything will ever beat that. In contrast, 5weeks later when we saw two eagles flying in the nesting territory, both without a GPS tag, and I lost contact with the tag I assumed the harness had broken and the tag had been lost.

Despite this I was excited about what we had learnt and the research went on. Since then we have GPS tagged a further two eagles, another of which did remove the harness after one month. This eagle can now be positively identified solely by the orange leg ring it has. The other of which is still flying the Cederberg skies and downloading data daily.

When I got home two days ago I checked the base station for any new downloads. I immediately noticed an old tag number appearing – It was the number of the first tag, somehow back in contact. I waited for what felt like a long 30minutes while the data was processed by out partners at UvA-BITS. When I saw the data I couldn’t believe my eyes. The day we lost contact with the tag was actually because the eagle flew a 75km journey Northeast of the Cederberg on a journey in which he travelled 110km in 2days. But even before he left his former territory, his apparently “life-long” partner was flying with a new male in front of his nest! So welcome home old “Pops”, these are highlights for me!

GPS tracks of a travelling eagle!

GPS tracking the Black eagle

Black eagles are known to occupy relatively small territories or home ranges (Davies 1994). However most estimates of home ranges have been deducted from nest spacing averages. Yesterday marked the GPS tagging of the third eagle for this study and as I am sat at my desk typing this the, first bit of data from that eagle has just come through!!

So what have we learnt so far?

The very first eagle was tagged in April this year in the Cederberg. Although the GPS device came off prematurely after only five weeks it still gave us the first insight into the actual habitat use of one of these birds. From that eagle we learnt that it used a core area of 23km² but covered a total of 50km² when we include data from one-off longer flights. This compares very nicely with Rob Davies (1994) estimation of a home range size of 24km² for Black eagles in the Karoo.

Cederberg eagle tracks

The second eagle was tagged last month in the Sandveld. After only a few weeks of data thus far we have seen a much larger home range. This eagle seems to have a core range of approximately 65km² and a total range of 92km². It seems to make longer flights, possibly travelling further on foraging missions to remnants of uncultivated land.

Sandveld eagle tracks

And now we have the third eagle, again tagged in the Cederberg. After a long wait of 30 hours in a hide over three days, we finally made a safe capture yesterday afternoon. The eagle weighed in at 3.5kg with a 2m wingspan.

Here he is, about to be set back on his way equipped with a top of the range GPS logger!!

I look forwards to sharing data with you from this eagle. I would like to take this opportunity to thank all of the sponsors for supporting this research - without you it would not have been possible - The Cape Leopard Trust, Driehoek Wine, Darling Brew, K-Way, Cederberg Cellars, EvoSat and the Animal Demography Unit!