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Foraging differences allow Frigatebird species to co-exist

Lab member Rowan Mott recently had a paper from his PhD research published in The Auk, which highlights his findings on how two similar congeneric seabird species can successfully breed side by side.

Traditional research methods document high levels of resource overlap in Great and Lesser Frigatebirds. Rowan used high-tech GPS tracking combined with chemical analysis of blood and feathers, to identify previously unknown differences in dietary and spatial aspects of the foraging strategies of these two species. The results indicate that body size differences between the two species influence the tropic level of the prey consumed, with the larger-bodied Great Frigatebirds taking prey higher on the food chain compared with the smaller Lesser Frigatebirds. During the breeding period, when adults are spatially constrained by the need to attend to an egg/chick, there exists considerable spatial overlap among species and sexes. However during the non-breeding period, when the demands of rearing a chick are removed, this overlap diminishes, with males of both species foraging further afield in offshore waters.

Read The Auk's blog about Rowan's research paper here.

Milestones

August was a busy month for three of the Phd candidates in our group, with Katherine Selwood, Rowan Mott and Shane Baylis all presenting the final seminars of their PhD candidature. Katherine also submitted her thesis titled "The significance and future prospects of floodplains for birds in a drying climate", and will soon commence a postdoctoral position at University Of Melbourne. We wish Kat the very best in her new research position.

Both Rowan and Shane plan to submit their thesis later in the year. In the meantime Rowan has been awarded a writing scholarship to complete his manuscripts for submission to scientific journals, and Shane is planning a cycling trip around Tasmania during November with his partner Nancy.

Monitoring with precision

New Monash University research has paved the way for drones to revolutionise ecological monitoring. Published in the journal Scientific Reports, the research found that drones are much more precise at monitoring the size of seabird colonies in tropical and polar environments than more traditional ground counts. Carried out on Ashmore Reef (tropical) and Macquarie Island (Sub-Antarctic), the research found that the ever-increasing precision provided by drones, along with the ability to survey hard-to-reach populations, may mean that wildlife monitoring projects move from traditional methods to drone technology.

Monash ecologist Dr Rohan Clarke explained that drones have already been used to monitor everything from the breeding success of canopy-nesting birds and to surveying elephants but nobody had yet tested if this method was better than more traditional survey techniques. “Until now, it has been unclear as to how precise drone technology might be when monitoring the size of populations of wildlife. Our latest research has demonstrated that a very high degree of precision can be achieved when using drone technology to monitor wildlife,” Dr Clarke said.

Lead author Jarrod Hodgson, who carried out the research while at Monash (and who is now at the University of Adelaide), explained how the research compared drone derived image counts with those made by humans on the ground. “Our team compared the precision of drone-derived image counts with those made at the same time by human counters on the ground for colonies of three types of seabird: frigatebirds, terns and penguins. Counters also monitored the colonies during the drone flights for signs that the birds may be startled by the presence of the drone,” Mr Hodgson said.

The authors found that counts using images captured by drones did not startle the birds and were consistently more similar than those taken from the ground. The authors suggest that the down-facing perspective of drone imagery reduces the likelihood of missing seabirds. In contrast, when counting from the ground, the terrain and other birds obscure the counters’ line of sight.

Dr Clarke explained the significance of these research findings to ecological monitoring projects. “It’s highly likely that in the future, drones will be used to monitor populations of birds and animals, especially in inaccessible areas where on the ground surveying is difficult or impossible. This opens up exciting new possibilities when it comes to more accurately monitoring Earth’s ecosystems,” Dr Clarke said.

A bird's eye view

UAV used to capture aerial imagery of nesting seabirds in NW AustraliaResearch Ecology, led by Jarrod Hodgson and Rohan Clarke, is partnering with ConservationDrones to use Unmanned Aerial Vehicles (UAVs or drones) for seabird monitoring. The Research Ecology team recently returned from a successful trip to remote islands in north-western Australia where high resolution images of nesting seabirds were captured using a UAV.

After some preliminary testing, we discovered that we could fly at an altitude of 75 m above ground level (agl) without causing disturbance to the birds in these environments. We also found that flying at lower altitudes would work for some large nesting species, but smaller non-nesting species were easily flushed from perching sites by the UAV at such heights. 

We targeted colonies of Crested Tern and Lesser Frigatebird for aerial survey. The Crested Tern colonies represent a medium-sized species that nests in dense colonies on the ground, whereas Lesser Frigatebirds are a large seabird which nests in smaller groups typically on elevated nest stacks and within vegetation. For every successful survey, experienced seabird counters made 1 or 2 blind counts of the surveyed population. Research Ecology will be comparing these ‘ground counts’ with UAV aerial counts to assess the reliability of UAV data.

Research Ecology is continuing to refine techniques which will allow for lower impact and more reliable aerial surveying of vertebrates. We are excited to continue our collaboration with the ConservationDrones team in several upcoming projects.

 

Mangrove forests important for terrestrial biodiversity

In a paper lead authored by Stefanie Rog in the journal Diversity and Distributions, the importance of mangroves for global, terrestrial vertebrates is revealed.

Stefanie conducted a review of the scientific literature published on mangroves, combined with open-source databases (WWF, ARKive and IUCN Red List).

The review found that 464 terrestrial species (320 mammals, 118 reptiles and 26 amphibians) use mangroves; five times more than previously reported. Of the 391 species whose conservation status has been assessed by ICUN, 35% were classified as threatened. Species were most often reported using mangroves for foraging habitat, followed by refuge, shelter, dispersal and breeding.

The highest alpha diversity of terrestrial invertebrates in mangroves occurs within Asia, northern Australia, West Africa and the Central American land bridge.

The terrestrial components of mangroves are often overlooked by society, and Stef's review extends our knowledge of mangrove forests and brings attention to these vital and undervalued ecosystems.

Read the full review in Diversity and Distributions here.

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