War and Peace Among Australian Dragons: Consequences for Communication and Social Behavior by Troy and Teresa Baird

We spent the fall semester of 2016 on sabbatical leave working with Richard Shine of the University of Sydney, New South Wales, Australia studying the behavioral ecology of eastern water dragons. Because our studies in 2009 were so successful, we returned to the same water dragon population located at Flynn’s Beach in the coastal community of Port Macquarie. Those studies resulted in the first quantitative description of the social biology of this very large (up to 1 kg) lizard, which is an iconic member of the NSW herpetofauna.

We were very surprised by what we discovered upon our return. The managers of our study site had undertaken efforts to restore the vegetation to native species characteristic of riparian zones in Eastern Australia. Their restoration involved removal of numerous large trees, shrubs, and vines to make way for the planting of native plants, particularly tall grasses to stabilize the stream bank from erosion during times of high water flow. Because the seeding of native grasses had only been in progress for six months, vegetation density was greatly reduced during the Austral spring of 2016 compared to what it was in 2009. It was immediately obvious that horizontal visibility for resident dragons was now greatly increased relative to 2009. Because water dragons rely heavily on visually-transmitted signals to communicate, we set about testing the effects of increased visual transmission social consequences behavior of individuals in this complex lizard society.

Marking lizards for individual identification quickly revealed 30% fewer adults relative to 2009. Because water dragons are long-lived (20 years) and strongly philopatric to very small areas, we expected that a significant number of the 2009 lizards would still be present. We were very surprised to discover only five survivors and that all of them were females even though 30 mature males and numerous immature males were thriving when we left in 2009. This high turnover rate, especially among males suggests that reduced cover may have resulted in significant predation by the large monitor lizards that also frequent this site, and that reduced cover may have allowed the most dominant territorial males to drive lesser competitors off of the site. Wright’s Creek had also experienced substantial flooding events over the previous three years which may have transported some lizards downstream.

The influence of decreased vegetative cover on social behavior and signaling among male dragons became apparent from records of social and spatial data on marked lizards. Vegetative cover is an important habitat variable in studies of animal signaling biology because it affects the efficacy of signal transmission and reception by senders and receivers. We were well prepared to take advantage of the changed vegetation at our site as an opportunity to test the effects of increased visual transmission on male behavior because we had previously recorded extensive data on both the behavior of mature males and the density of vegetative cover, especially visibility at ground level (the lizard’s eye-view). By replicating collection of these same data in 2016, we can test the consequences of increased potential for transmission of visual signals and diminished potential for subordinate males to hide owing to reduced plant cover.

Analysis of this large 2016 data set is on-going, so findings at this point are still tentative. Much about the intensely aggressive social structure among males that we documented in 2009 was altered in 2016. A subset of large males still defended reproductive territories, but there were 35% fewer socially dominant males (9 compared with 14), and determining their social status from observations of male advertisement behavior was even easier because the non-territorial males displayed so infrequently. Aggression among mature males was exceedingly intense in 2009 because in addition to the 14 territorial males, 16 equally large non-territorial males were also very active on this same study site. Only seven non-territorial males were present in 2016, and they were seen only infrequently, compared with daily sightings in 2009. We also discovered that non-territorial males were travelling surreptitiously within the extensive under-ground system of pipes draining into Wright’s Creek. Although temporary removal of individual territory owners in 2009 prompted intense two-day long contests before one non-territorial male emerged victorious, replication of these experiments in 2016 revealed that much less aggression was required before one non-territorial male to assume control of territories made vacant experimentally.

Reduced vegetative cover also appears to have greatly increased use of visual displays to advertise territory ownership instead of patrolling aggressively. Males frequently climbed up tree trunks or perched on elevated rocks because they could view their territories and signal their rivals without patrolling which is energetically expensive. Increased reliance on visual signaling was further suggested by heightened territorial male responses to experimental introduction of a model lizard intruder. Even though aggressive contests among males were less frequent and intense than in 2009, we did observe and record some contests, which grows our total data base that we are using to understand the evolutionary dynamics of how animals resolve contests in nature. We will also use our two-season data set to address other questions such as how changed visibility and cover may influence the fitness costs and benefits governing the size of defended areas and relationships with individual females. Lastly, even though visual signaling is well developed in these lizards, we also plan to use a sample of lizard glandular secretions to begin exploring the possibility of chemically-based signaling.

Returning to Port Macquarie also gave us the opportunity to fully re-immerse in an entirely different flora, fauna and culture. The Australians were in all ways welcoming and supportive of our work. We were able to reconnect with old friends and make many new friends. We interacted with visitors to our site nearly every day, giving many impromptu seminars about water dragons. Australia never failed to put on a spectacular wildlife show for us: breaching and tail slapping humpback whales, bellowing male koalas in search of mates, goannas uncovering and gobbling up more than a dozen turtle eggs at a time, and massive yellow-tailed black cockatoos shredding banksia seed pods outside our apartment window – just to name a few… Both Teresa and I look forward to all opportunities for sharing our experiences: the science from me when data are analyzed, and beautiful photography from Teresa. We greatly appreciate all support for this opportunity from the Department of Biology, the College of Mathematics and Science Dean's Office, the Office of Research and Sponsored Programs, and the Office of Academic Affairs.

Drs. Troy and Teresa Baird

Troy and Teresa Baird weighing a female water dragon.

Troy Painting

Troy Baird painting identification numbers on a female water dragon.

Face Off

Two territorial male water dragons facing off prior to fighting over a contested territory border.

Teresa Baird

Teresa Baird holding the largest territorial male on the field site in 2016. Note bright red color patches on the abdomen that are used in signaling.