The Cape Bird Club

Courses - Birds and Climate Change by the ADU Team.

photograph by Priscilla Beeton.

Vernon Head (CBC Chair), Dieter Oschadleus, Sally Hofmeyer, Les Underhill, Peter Steyn (CBC President).

On Saturday 23 July, the club presented a course on the impact of climate change on birds. The series of talks was put together by Les Underhill and his team of scientists from the ADU (Animal Demography Unit) of UCT’s Department of Zoology.

First up was Res Altwegg, a statistical ecologist, who explained how ringing data is used to predict probability of survival in Blue Cranes. Re-sighting of ringed birds, both adults and juveniles, and recovery of dead birds, yield valuable information about reproduction and survival rates. Res also looked at how Blue Cranes are influenced by rainfall - total amount, seasonality, and variance. He concluded that higher rainfall levels are beneficial to the cranes - early season rain means more eggs will be laid, and late season rain means a better rate of survival of fledglings. He stressed that predictions are based on what is known thus far, and there is a need to keep on monitoring using CAR counts and ringing retrieval data.

Andrew Jenkins was the next speaker. Andrew has been monitoring Peregrine Falcons for several decades across the Peninsula, from Tygerberg Hills to Cape Point.
These charismatic raptors have a widespread distribution, but the population was seriously diminished by the use of pesticides such as DDT in the 1970’s. An intensive conservation campaign led to a tremendous recovery and Peregrines have become a conservation icon. In Cape Town itself the population has increased significantly, with several factors probably contributing to their success. “Urban subsidy” may be aiding the city birds - they have plenty of high perches from which to hunt, and there’s a large prey base of doves, starlings and sparrows. In some cases nest boxes have been provided, and breeding success further increases during warm, dry spring weather.
These are aggressively territorial birds and they pair for life, which makes it easier to monitor them.

Res was back next, talking about changes in the timing of biophenomena - plants sprouting earlier and caterpillars emerging earlier, which means that birds need to breed earlier to catch the peak in food abundance. These phenomena are most noticeable in the Northern Hemisphere where the seasons are more clearly defined. Migrants like Barn Swallows must leave their wintering grounds earlier and arrive at their breeding places when the temperatures are right for insects to be available for their chicks. The picture is far from clear at this stage but in some regions the swallows are leaving earlier and returning later. Res described how moult data can also be used to see changes in the annual life cycle of the birds. He stressed the importance of SAPAB data in these studies, and urged more people to become involved. The more data the better; the more lists per pentad, the better!

Next up was Rene Navarro, talking about his techniques for analysing data on Cape Gannets. He told how gannets have been around for millennia and have survived several extreme changes in climatic conditions, including ice ages. What they have to adapt to now is the change of food available to them within their foraging ranges. The best nutrients for their chicks are found in sardines and anchovies, but this food source has been moving southwards and eastwards in the ocean around the Western Cape. The distance they would have to travel is just too far, and gannets have had to fall back on the less nutritious foods within range - hake (fishery discards) and saury. (What is this word????) However the chicks don’t fatten up to the same extent, and may not be strong enough to cope with their changing environment. Over-fishing is also a huge problem that lowers survival prospects for the Cape Gannet.

Les told how he was fortunate enough to visit the Taimyr Peninsula in the Siberian part of the Arctic tundra, during the early 1990’s. The tundra with its rich abundance of insect food in its short summer, has supported the breeding of huge numbers of shorebirds, including Curlew Sandpipers. But wader numbers are decreasing alarmingly across the world. Curlew Sandpipers are hatched in the tundra, fledge within 15 days, and within one month of hatching are ready to migrate south with the adults. They fly 12 000km over 7 weeks, re-fuelling along the way. Warmer temperatures in the tundra have led to their breeding 6 weeks earlier than historically. As the ice shrinks northwards and boreal forest spread north, suitable habitat for shorebirds to breed is reduced. Sea level rise at stopover sites, mis-timing of arrival at the tundra, and reclamation developments that destroy habitat, have all reduced the total population of Curlew Sandpipers. He described how CWAC counts at Langebaan Lagoon where the curlew sandpipers overwinter have been shown to be a fairly reliable monitor of breeding success rate exactly one year after breeding has taken place in Siberia.

Sally Hofmeyer focussed on the decline of the Southern Black Korhaan, birds which prefer bushy natural vegetation to agricultural lands. As areas are farmed more intensively, the numbers in parts of the Western Cape have decreased by up to 80% (but in the Eastern Cape Karoo they have increased by 50%). Although the literature on these birds is insufficient, habitats are expected to change as rainfall patterns change. The vegetation type is likely to become more grassy, offering less of the thick cover Korhaans prefer. The prevalence of Pied Crows may also be a factor in their dwindling numbers.

Dieter Oschadleus talked about irruptions of Red-billed Quelea, one species that has increase its range. He described the breeding, roosting and foraging habits of these birds which unfortunately have become an agricultural pest that will need management as they move into grain fields when their natural seed supply runs out. Range changes are probably the result of land use changes, rainfall patterns and other factors. Climate change may provide the impetus for these birds to look around for new areas. He stressed the importance of learning more about these birds and that birders could help by providing data via the Atlas Project, Phown, Safring and by reporting every incidental sighting.

Les wrapped up the day, saying that climate change is just a part of the picture, and a more accurate term to describe what is happening, would be ‘environmental change’. He suggested ways we can help as “citizen scientists”, gathering data for the ADU’s scientists to gain a more complete understanding of biodiversity and the changes it is undergoing. We can get involved in bird-ringing, waterbird monitoring, CWAC and CAR counts, and of course, the SABAP-2 atlasing project. By adding our efforts to these projects, data-collection increases exponentially. Another benefit is the simultaneous collection of data - impossible for a handful of scientists to do. All data collected for the various projects are of great value to conservation as they are used to motivate conservation action projects.

Isabella Hayden.