My research has covered a broad range of ecological concepts, but they all have one thing in common: how are anthropogenic-induced changes to our planet affecting birds.
For my Post-doctoral Fellowship I am examining how habitat type is affecting behaviour and reproduction in Arabian Babblers.
For my Masters and PhD I collected data looking at how climate change may be related to decreasing sightings of Cape Rockjumpers.
For my Honours I examined how noise may be affecting communication in adult Tree swallows provisioning their young.
While small human settlements may provide increased resource availability, these oases can attract invasive competitors and predators. Using the ground-breaking technology available through the high-throughput ATLAS tracking system, I am examining behaviour and reproductive success of desert-specialist birds (Arabian babblers) in a mosaic of human-dominated habitats in the Israeli Negev. The ATLAS system allows for a unique understanding of inter- and intra-specific group movements and social dynamics throughout the year, while we also examine how reproductive success changes based on type of habitat across the gradient of of human-modified habitat. Check out the new website.
Above: A newly tagged babbler having her photo taken to record ATLAS number, colour combo, and time of release.
Above: First ATLAS antenna, setup on the SIDR building in Midreshet Ben-Gurion, overlooking the old floodplain of the Tzin river.
Below: The "morning dance" of the babblers, a group grooming and socializing ritual that reinforces bonds and possible changes allegiances ;)
Evidence of the impact of climate change on our collective environment has been highlighted by many scientific studies in over the past two few decades. However, there are still many gaps in our understanding of the consequences of global warming and in particular of its effect on biodiversity. Although international communities (e.g. IUCN) often focus on range-restricted species in the polar regions, another often overlooked ecozone are is high alpine habitats, or “sky islands”. Sky islands have large proportions of endemics and their mountain-top locations leave inhabitants with no little opportunity to move to higher (and thus cooler) habitats as their current habitats continue to warm.
The Cape Rockjumper - a South African endemic bird species – is suffering population declines that are heavily correlated with habitat warming within its current range. Cape Rockjumpers are restricted in their distribution to the mountain slopes of the Western and Eastern Cape provinces: the “sky islands” of south-west South Africa. My goal was to try and find the mechanism for this decline, in the hopes we can find a way to bolster not only Rockjumper populations, but those of other similarly affected species.
To do this, I have examined Rockjumper behaviour, reproduction, genetics, and physiology. While generally considering these aspects in relation to temperature, there have been a few surprising findings along the way.
After doing full day observations of 11 Rockjumper family groups over a 13 month period, we had a massive amount of data showing how Rockjumpers respond behaviourally to increasing temperatures (published in Animal Behaviour). Results suggest while they are able to buffer against high temperature by using cool microsites, this resulted in decreased time spent foraging (below left).
Despite general patterns showing birds move into shade at high temperatures, birds continued to forage (foraging = 1) more often in sun (grey, dotted line). This suggests the need to forage may outweigh physiological consequences of spending time in warmer locations, and was especially common in females.
Over 100 individuals (both adults and juveniles) have been given individual colour ring combinations at Blue Hill Nature Reserve, allowing us to keep track of who's who (so long as we can get close enough to see them!). All of our tracked families had at least 50% of the group ringed, with families ranging in size from pairs of two to groups of five. (below right, female green-yellow-green "Gyggles").
Finding Rockjumpers is by far the hardest part of my research. Myself along with volunteers traverse the Fynbos mountains of SW South Africa hoping for any sight or sound. Even a small group of 2 individuals may have a territory of up to 10 hectares (100,000 square metres), and they are often difficult to spot as they hide behind rock outcrops.
Our rockjumper reproduction research had two main questions: 1 - how does adult behaviour at the nest change related to temperature? 2 - how does predation and overall nest success change related to temperature and fire?
Results from video footage showed adults provisioned less often at temperatures above ~ 22.4 °C, which corresponded to less mass gain in nestlings (published in Journal of Avian Biology). Our nest photos showed birds had greater nest success in areas with recent fire (surprising as usually more vegetative cover means less success), and nests had lower predation on days with cooler temperatures (when snakes were less active)(published in Ibis).
Right: Outcome for 54 Rockjumper nests found between 2016-2018 (2016 = 2, 2017 = 17, 2018 = 35). When we could determine the cause of predation it was predominantly Boomslang (n = 17 plus 1 partial). Only 8 nests fledged over the
three years (2017 = 1, 2018 = 7).
I also made a few videos of nest footage, which I put on my YouTube channel and on the Cape Rockjumper page for Birds of the World.
Left: Not surprisingly, hourly provisioning rate was positively correlated with mass increase in the nestlings. However, provisioning rate decreased at increasing temperature, and so we can extrapolate that nestlings would gain less mass at higher temperatures.
For genetics, I was interested in overall structuring of the sky island populations. Namely, how do Rockjumpers disperse from mountain ranges that are separated by up to 30km of hot Karoo? I went to 8 different ranges for Cape and two for Drakensberg to collect samples.
I examined genetic diversity, variation, and inbreeding potential in three genes (one nuclear and two mitochondrial). DNA extraction and PCR amplification was done at Rhodes and then samples sent to Macrogen in the Netherlands for sequencing. I have been lucky enough to have a lot of participation, from Tygerberg Bird Club, Cape Nature, BirdLife SA, volunteer assistants, and private land owners, without which this could not happen.
Results have been surprising... Cape Rockjumpers have very low overall diversity, which may indicate a past bottleneck, or may be from having such a specialized habitat.
Right: Map showing location (and sample size in parentheses) for sample collection. While past occurrence records suggested I catch a few birds at Tsitsikamma and Lady Slipper, I was unsuccessful at Tsitsikamma and found no evidence for birds at Lady Slipper (edge extinction?).
(Currently the pre-print is online at Authorea and will be combined with rad-sequencing data once permits are cleared to get our samples to California).
My MSc consisted of two chapters on the seasonal physiological flexibility of Rockjumpers; the first was on their response to cold, the second was their response to heat. Surprisingly (for us), we did not find that Rockjumpers were that well-adjusted to their often cool environments, and we also did not find they were that poorly adjusted to heat.
We published our seasonal responses to heat as well our article on heat comparisons between juvenile and adults (in Journal of Ornithology and Ostrich respectively). Interestingly, Rockjumper cold tolerance seemed to indicate Rockjumper's "fit" better with earlier branches of passerines (the sub-oscines) than their closer oscine relations (published in Journal of Thermal Biology).
Bottom left: A Rockjumper in one of our snap traps, my first ever bird caught! We kept the first 5 birds for 48 hours (to do heat, cold, basal metabolic rate, and themoneutral zone), and the next 12 for 24 hours. Birds were fed mealworms ad libitum and released (generally fatter) at the same location we caught them. Bottom right: "Gigantor" –– the largest Rockjumper ever captured (65 grams!!), in his fully puffed up stage during a cold tolerance run. I monitored birds live using a GoPro, red light, and the GoPro live-feed app on my phone.
Noise and Swallows
The world is getting louder, and wildlife are having to adjust. For my Honours I added white noise to Tree Swallow nests for 3 days and then filmed provisioning to see how parents and nestlings responded. With noise, nestlings begged more emphatically, and parents gave more contact calls to stimulate begging, but to no obvious detriment, as mass and fledging were not significantly different (published in Animal Behaviour).