The breeding ecology and behavioural adaptations of African Black Oystercatchers in light of climate change
PhD data
This dataset is for the PhD thesis titled: The breeding ecology and behavioural adaptations of African Black Oystercatchers in light of climate change
Abstract: This thesis examined how weather conditions and other environmental factors influence the vulnerability of nesting African Black Oystercatchers Haematopus moquini (oystercatchers) to climate and habitat change. I explore, for the first time, the behavioural adaptations used by the species to cope with breeding in a limited strip of beach, between high tides and terrestrial predators, and with little nesting shelter, and their breeding decisions to maximise breeding outcomes. Behavioural and breeding data were collected over three breeding seasons (2016—2018) on Robben Island, South Africa (a site with about 5% of the global population of the species) using time-lapse digital cameras and direct observations. Climate and environmental variables were obtained either through on-site iButton data loggers or from the relevant South African meteorological agencies. The results show that oystercatchers are vulnerable to increasing heat loads as temperature increases. However, oystercatchers used a suite of thermoregulatory behaviours to cope with a wide range of environmental temperatures and decreased the length of their incubation bouts as temperature increased. The proximity of the oystercatchers’ breeding site to the ocean appears to contribute significantly to their capacity to cope with increasing heat loads. But such sites potentially expose the oystercatchers to the risk of nest losses to storm surges. Oystercatchers reduced this risk by using habitat selection to optimise the placement of their nests close to the midpoint of the beach, but some were constrained by the narrowness of their territories. Oystercatchers also used the biweekly semilunar spring tide cycle to synchronise the incubation start date of their clutches probably to minimise the number of spring tides that they experience during incubation. Predation was the main cause of oystercatcher nest failure. Surprisingly, Mole Snakes Pseudaspis cana were responsible in all cases where the predator identity was known rather than Kelp Gulls which have historically been suggested to be the main agent. Nest predation probability was influenced by temperature and distance to predator-concealing vegetation and increased as more nests became available, causing a seasonal decline of nest survival. Hence, oystercatcher pairs laying large clutches early in the season were more likely to produce one juvenile in a season. The average number of fledgelings per pair per season was 0.38 and close to that (0.35) required to maintain a stable population. These findings improve our understanding of the breeding ecology and behavioural adaptations of the oystercatchers which might help them to cope with climate change as well as provide new insights on which management decisions and further studies can be based.
The thesis has five data chapters (chapters two through to six) as follows:
Chapter Two: Cues for nest-site timing and selection by African Black Oystercatchers: Effects of semilunar spring tide periodicity and breeding habitat width
Chapter Three: On-bout thermoregulation behaviours used by African Black Oystercatchers to cope with varying temperatures during incubation
Chapter Four: Incubation scheduling by African Black Oystercatchers: Effects of weather, tide phase, and time of day
Chapter Five: The relative importance of different nest predators and predictors of nest predation in African Black Oystercatchers
Chapter Six: Population size, breeding parameters and predictors of breeding success of African Black Oystercatchers on Robben Island
For ease and clarity the data has been grouped by chapters and uploaded as such. So for the data analyses described and the results presented in each chapter, there is a corresponding datafile that has been uploaded. The r script containing the analyses described in each thesis chapter has also been added to the datafile of each chapter.
The general folder contains other details that were not directly used in the analyses but were used to inform some of the chapter specific datasets and also some aspects of the discussions in the thesis. For example, the biometric data and eye fleck images in the general folder was not used directly in any of the chapter specific data analyses, but it informed the determination of the sex of the oystercatchers which enabled their designation as either male or female. Also the egg measurements presented in the general folder informed the estimation of the incubation start date/age of the nest as used in the chapter specific analyses but were not in themselves used directly in the analyses.
The spreadsheets in the folders contain datapoints. The column is either self explanatory or has been described under a heading 'key' at the right hand side of each of the spreadsheets.
More details about the thesis and description of the data analyses are presented in the thesis under the general methods and in the data analyses section of each chapter. The thesis can be downloaded for free from the OpenUCT website at: thesis_sci_2021_azaki bukola debola aderewa.pdf (uct.ac.za)
