2013 Season Report
I’m writing this from the cottage I have been living in for the last two years at Driehoek. If I look over my shoulder Tafelberg stares down at me and if I take a step back and do a 360° turn I can pinpoint four separate Black eagle nests on the distant mountains. The Cederberg has been my home and the heart of my research since 2011 and as my fieldwork is coming to an end I know I will sorely miss it.
Over the three years the eagles have never failed to amaze me and with the beginning of each breeding season I have closely followed the nests with great anticipation to see who will breed each year.
|Figure 1: Graph showing the percentage breeding outcomes for the Black Eagle in the Cederberg and the Sandveld 2011-2013.|
Figure 2: The main road leading out of Driehoek, in the Cederberg, on 30th Aug 2013.
This year saw some meteorological surprises and trials, with the morning of the 30th August being a white out snow fall which buried at least one chick and kept me well and truly wrapped up in a down jacket! The chick, which was captured on the nest camera, managed to shake free of the snow and his endurance saw him fledging at 89-91 days old at the end of September.
Figure 3: Black eagle chick 59 days old standing in the nest laden with snow.
Heavy rainfall throughout winter created its own obstacles. With the regular flooding of the Cederberg roads, it quite literally at times became impossible to get out and see the eagles. But water levels generally dropped by the following day and I was usually grateful for an excuse to stay at home and catch up on data entry.
Figure 4: The Driehoek road bridge in flood.
I have continued with my investigation into the diet of the Black eagles in both the Cederberg and the Sandveld, in hope of reflecting upon their adaptability to changing environments. This year, with the enthusiastic and voluntary help of some very experienced climbers, we installed six nest cameras. As the chicks have only recently fledged I am still to retrieve the cameras. We will do this in November, when I hope to be dangling on the end of the rope myself! After this it will be the tedious, but likely fascinating, task of analyzing around 80,000 photographs for prey deliveries.
Figure 5: Adult Black eagle feeding a chick on Hyrax, also on the nest Mole rat and Cape francolin.
Click on the video for an exciting insight into 'a day in the life of an incubating Black Eagle'. This is compiled from time-lapse photos at three minute intervals.
The GPS component of my research has been one of the biggest challenges but has also yielded the highest rewards. Initial data downloads have been exciting to receive and have produced some stunning outputs. Figure 6 shows high resolution data collected at three second intervals, which allows us to see the precise movements of an eagle catching a thermal.
Figure 6: High resolution tracking data collected from an eagle in the Cederberg.
2013 also saw the successful tagging of a further two adult eagles in the Sandveld bringing the total number of eagles tagged for the project to five. Snapshots of their data are represented in Figures 8 and 9.
Figure 7: A Black eagle with a GPS tag is released in the Sandveld.
In July, I was stunned with the return of one of our tagged eagles. He was initially tagged in the Cederberg but after apparently being ousted, has now travelled northeast into the Karoo and as far south as Porterville. Although he appears to spend most of his time in the Karoo he has continued to regularly ‘visit’ the Cederberg and download his data. I am looking forwards to getting stuck into data analysis in the coming year to understand these movements more clearly.
Figure 8: GPS data collected from two eagles in the Cederberg.
Figure 9: GPS data collected from three eagles in the Sandveld.
Through hiking and aerial surveys a total of 112 nest sites have now been located on cliffs in the study area. This year I monitored the breeding outcomes at 36 sites with help from Cape Nature on the Cederberg side. This now gives a good basis of information to work from to review the overall population status and breeding output. I also look forwards to making spot checks on their progress through 2014.
So it is with my deepest thanks that I end this report. Over the years I have received generous sponsorship from the National Birds of Prey Trust, Driehoek Wine, K-Way, the Cape Leopard Trust, Darling Brew, Idea Wild, Bridgestone, Donkies Kraal, Evosat and Cederberg Cellars. Dawie and Lizette Burger have given their boundless support and encouragement from Driehoek. Staff and volunteers at Eagle Encounters have enthusiastically supported my work both at the center and out in the field. Patrick Banville gave a full seven months of his time and skills to helping me throughout the 2012 monitoring season. Pilots from Base4Aviation have kindly donated their flying time and skill to the project by performing the aerial surveys. The Sandveld community have made me welcome and shared their homes with me. While many countless people have freely given their encouragement and interest, which has kept my motivation throughout – my thanks to you is endless.