Christina Buelow researches how the movements and behaviours of birds can link different habitat types together, and how this impacts the wider coastal landscape.
Along the eastern coast of Australia you will find sandy shores, wetlands, estuaries, rainforest, mangroves and more. The coastline is covered with complex arrangements of different habitat types, each supporting their own intricate web of animal and plant interactions. While many land animals can move between different habitat types, its their aerial counterparts that truly connect these varied patches of landscape.
Originally from Canada, Christina moved to Townsville, Australia to undertake her PhD with Professor Marcus Sheaves at James Cook University. After reading about some of Marcus Sheaves’ research on fish connectivity in estuaries, Christina realised that if she could apply the same concepts to coastal bird communities she had found her ideal PhD topic.
Along the Queensland coast, birds can often be found in great diversity in small areas. Christina has been investigating how birds can facilitate connectivity between different coastal landscapes, and in turn how this connectivity impacts these ecosystems.
Mangroves are an ideal habitat to start with this question. Lots of birds roost in mangroves, but few stay to feed because unless you have a taste for mosquitos, or have the skills to catch crabs and mudskippers, there isn’t really much to eat. One of Christina’s projects has been to find out where these birds go to feed, and indeed, what they are feeding on.
There is a fascinating technique called stable isotope analysis, which allows scientists a window into the feeding habits of an individual animal based on the chemical signatures of samples taken from that animal. The carbon and nitrogen content of the sample provides an indication of diet, which can then be matched with chemical signatures from various food sources. The carbon signature can tell you where the individual is feeding, and the nitrogen signature can indicate what they are feeding on, and gives a rough idea of their position in the food web.
Christina and her volunteers surveyed bird communities up and down the coast. Using mist netting to catch the birds, they took a claw sample and a blood sample from each individual to be used for stable isotope analysis. These two different samples types provide some interesting variation in the analysis. Analysis of the blood sample alludes to recent feeding habits, that is, over the last few weeks. Then at the other end of the scale, the claw sample gives insight into the longer term diet, from months to years.
Delving into the details of feeding behaviour allowed Christina to understand the role that birds play in coastal connectivity. It is a complicated role, and not all birds contribute equally. Specialist feeders, picky eaters who prefer nectar or seeds for example, tend to stick to only a small number of habitat types. While the generalist feeders (carnivores and insectivores) travel further to forage and cover a greater variety of coastal habitats, thus generating habitat connectivity. But is this connectivity actually useful to the persistence of certain ecosystems?
This intriguing questions forms the next stage of Christina’s PhD research. In order to answer it, she is conducting a case study using the Pied Imperial Pigeon found in high density breeding groups on inshore islands during the Australian summer.
Christina is now studying whether this species – who roost in island mangroves and forage over the mainland during the day – are producing a nutrient subsidy in the mangroves where they sleep.
In order to answer this, Christina has been measuring the quality and composition of nutrients on mangrove islands with and without bird colonies. By analysing the nitrogen, carbon and phosphorus content in soil, leaves and herbivorous insects, Christina will be able to determine not only if a bird-contributed nutrient subsidy exists, but also how far up the food chain it reaches.
The next step for Christina is to tease out the effects that a nutrient subsidy could have on the ecosystem. Many mangrove islands in Queensland are surrounded by coral reefs, so is there potential for a ripple effect on to other systems? A change in nutrient conditions on coral reefs can have devastating impacts, but perhaps an island nutrient subsidy is just part of a environmental equilibrium that has been present for centuries.
As Christina wraps up her PhD research and brings together her thesis she is looking for post-doctoral opportunities in community ecology and spatial modelling. Christina’s positive PhD experience is reflected in many international research students, who have chosen to come to Australia for its incredible landscape and biodiversity. Talking to PhD students can provide an insight into some of the incredible scientific research that is being conducted in Australia, and particularly in north Queensland.
Publication:
Buelow C and Sheaves M. A birds-eye view of biological connectivity in mangrove systems. 2015. Estuarine, Coastal and Shelf Science. Vol 152.
Images:
The photos used in this story were provided by Christina Buelow and taken by Christina Buelow, Rachael Payne and Claudia Trave, as indicated in image captions.
The feature header photo of a Sacred Kingfisher was taken by Rachael Payne.
Jo Khan 
Wonderful blog and the kingfisher is a star!
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