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Reisverslag Wat heb ik nou 5 maanden gedaan?
20 januari 2014
Wat heb ik nou 5 maanden gedaan?
African Black Oystercatcher & Kelp Gull disturbance project.
‘Times flies when you’re having fun’ and after 5 months of hard work and fun Shirley’s internship at Nature’s Valley Trust is almost at its end. During these 5 months you may have noticed us on the beach, not dressed in bikinis but shorts, a fieldwork shirt (often with poo on it), and a hard hat. Although seen as overdressed for a morning on the beach, this attire was necessary for the research project on the influence of human disturbance on the African Black Oystercatcher and the Kelp Gull nesting at the Peninsula, Lookout and Robberg.
As part of her project Shirley marked and monitored all the African Black Oystercatcher nests she could find in all 3 study sites. There are 8 nests on the Peninsula, laying in total 13 eggs of which 3 eggs/chicks were predated, 4 eggs/chicks died a natural death and 5 of the eggs hatched. On Lookout there are 7 nests laying in total 14 eggs of which 8 eggs/chicks were predated, 1 egg/chick died a natural death and 5 of the eggs hatched. Robberg had the highest predatation rate of all the areas, 8 of 12 eggs laid over 5 nests were predated. Scary facts!
Shirley did un-manipulated disturbance trials and manipulated disturbance trials. For the un-manipulated disturbance trails Shirley sat and observed the behavioural reactions of the birds to walkers, sunbathers/picnickers, joggers and dogs either on/off the leash. Manipulated disturbance trials involved walking in a straight line to a bird (on a nest during breeding season) and dropped markers when behavioural reactions were displayed. Shirley then measured the distance from the nest to each marker to get an idea of how far we (humans) need to be from the breeding birds to prevent disturbing the birds.
As the research progressed Shirley noticed different behavioural reactions in the breeding African Black Oystercatchers and Kelp Gulls. Breeding oystercatchers incubating eggs would initially walk off the nest before calling on direct approach while gulls would initially starting calling and then walk off the nest, and if you go too close would begin mobbing. This is due to different nest protection strategies: the oystercatcher protects it’s nest through camouflage and distraction while the gull protects it’s nest through aggression and intimidation. Aggressive gulls are the reason that hard hats, seemingly ridiculous on the beach, became necessary; having your head attacked by a protective gull is not at all pleasant!
Not only were the order of reactions different between species, but Shirley discovered that the oystercatchers were more sensitive to her approach and would react when she was much further away from the nest than the gulls did, where she could come much closer. Another trend that was seen was the difference in reaction distances between the 3 study sites. Both species were more sensitive to Shirley’s approach at Lookout, and walked off the nests sooner than in the other 2 areas. The birds on Robberg reacted the slowest of all 3 study sites. This may be due to the breeding site location: birds nesting on cliff edges may struggle to see Shirley’s approach while birds nesting in open areas may be more accustomed to the presence of people who are restricted to the boardwalk.
Another aspect of the project looked at how long it took birds to return to the nest as well as how long it took them to continue brooding. There was a big difference in time between the two species. Gulls returned very quickly, while the oystercatchers took far more time to return back ensuring that the location of the nest was as concealed as possible. Looking at these results over the 3 study sites showed that return times for gulls were quite similar over 3 sites, while the oystercatcher had the fastest and lowest return and brooding times on Robberg. This can be explained by differing nest locations.
Mark and Minke will continue with the work that Shirley has begun after she leaves until the end of the breeding season. This will complete the data set and show the whole story of disturbance effects. Shirley will leave Plett with a big smile on her face from all the amazing things she has learnt and experienced during her time with Nature’s Valley Trust, but also with a tear in her eye knowing she will miss the birds, the people and Plett a lot!
Shirley Van de Voorde and Minke Witteveen
20 januari 2014 11:42 | Door: zus
Go for it girl, you can do it!
20 januari 2014 14:35 | Door: Ridette
Heel veel succes vanavond met de presentatie van je werk!
We duimen voor je!
Hans en Ridette.
20 januari 2014 19:46 | Door: Stephanie
20 januari 2014 22:22 | Door: Marinka
Het is zooo snel voorbij gegaan of niet? Succes met je presentatie!