In tropical northern Australia,about 60 km east of Darwin, the Adelaide River winds through the low-lying landscape to form a huge meandering floodplain. Fogg Dam lies on a small tributary of that floodplain, and Beatrice Hill forms an area of higher ground to the east, near the Arnhem Highway.
Fogg Dam lies within the “wet-dry tropics”, with a really distinctive climate. It’s hot all year, with maximum daily temperatures close to 32oC year-round. However, the nights are much cooler during the dry-season (mid-year) when there are few clouds to keep the heat in. During the “build-up” (October-November) and the wet-season itself (December-February) the temperature can hover around 30oC all night as well as all day. More importantly for most people, the humidity at this time of year is incredibly high most of the time … and so it can be desperately uncomfortable. It’s no accident that Rick commenced his tropical field program at about the same time that air-conditioning became widely available in the “Top End”! However, some of the members of Team Bufo are a lot tougher than Rick – despite his Canadian heritage, Greg Brown actually looks forward to the warmer weather!
As the names “wet-season” and “dry-season” suggest, the rainfall patterns are incredibly seasonal. The landscape becomes progressively drier through the long dry-season, and wildfires are everywhere, but the onset of monsoonal rains changes that situation dramatically. Almost overnight, the vegetation begins to burst into life. The savannah woodland is fairly uniform – dominated by Darwin wooly-butts and stringy-bark trees – but the understory of grass and shrubs responds quickly to the increased moisture levels.
And the fauna responds as well. With the changing of the seasons, the bird species change – desert species head back down south to the drier country, and many of the waterbirds (geese, ducks, egrets and the like) that have congregated around the shrinking water bodies can disperse across the landscape. The native frogs have mostly spent the dry-season inactive in burrows or hidden in tree-hollows, but they emerge with the first rains and many begin to breed as soon as water bodies form. Some of the small reptiles also are inactive during the Dry, and become more active as the Wet arrives. For example, the spectacular frill-necked lizard hides away in tree branches during the Dry, but can be seen scurrying on its hind legs across the ground as soon as the rains arrive.
Many people think of the tropics as being the same year-round, but the
wet-dry tropics are incredibly seasonal – the main thing that changes
from month to month is not temperature (as in southern Australia) but
rainfall. And so we see really strong seasonal patterns of activity in
most of the local fauna, and reproduction is restricted to specific
seasons. For example, keelback snakes and water pythons at Fogg Dam lay
their eggs in the dry-season, whereas slatey-grey snakes lay during the
wet-season. For most species of native animals, of course, we still
don’t know what times of year they reproduce – the tropics have an
incredibly diverse fauna, and we know very little about most of them.
What animals can a tourist expect to see at Fogg Dam? Well, it depends very much on what time of year you are there, and what time of day. Just about everybody will see a lot of waterbirds – egrets, magpie geese, whistling ducks, burdekin ducks, and the like, with an occasional jabiru or brolga. On the roads, hawks are very common; a plume of smoke from a wildfire during the dry-season can bring literally hundreds overhead. For the experienced birdwatcher, there are lots of less common species – for example, the rainbow pitta is a gorgeous inhabitant of the monsoon forest fringing the dam. And people from southern Australia will see lots of familiar birds, from spur-winged plovers to magpie-larks.
Mammals are harder to see, except for agile wallabies in the woodland; these beautiful little wallabies move out into open areas near dusk. Dingos are common, and anybody driving the roads after dark may well see smaller mammals like northern brown bandicoots, water rats, dusky rats, and small planigales (carnivorous marsupials). The numbers of dusky rats, in particular, are quite astonishing – surveys suggest that the featureless floodplain often contains literally tons of rats per square kilometre. They live almost the entire time down cracks in the floodplain soil, so are hard to see even when they are common. Feral cats and wild pigs are regular visitors to Fogg Dam also.
As you'd guess from it being TEAM BUFO's primary study site, reptiles
and amphibians are diverse and abundant at Fogg Dam also. The cane
toad invasion has killed most of the big floodplain goannas but they
seem to be making a comeback. The smaller goanna species in the
surrounding woodland seem to have been less affected by toads. Elegant
little two-lined dragons and the extraordinary frillneck lizards are
common also. Skinks of various kinds zip rapidly through the open
spaces by day, sometimes pursued by equally quick whipsnakes. At night,
geckos emerge from their daytime retreats to feed on bugs by lighted
windows, and the snake-like Burton's Legless Lizard prowls across the
land. A walk along Fogg Dam at dusk likely will reveal skinks and
snakes, with perhaps a long-necked turtle or two, and the eyes of both
freshwater and saltwater crocodiles reflecting the spotlight from out in
the water. The most common snakes - water pythons, keelbacks and
slatey-grey snakes - have all been longterm study species for Team Bufo,
so will be described in more detail in other pages.
The Friends of Fogg Dam web site is worth visiting for more information.
For the full story about the cane toad invasion of Australia, and what we can do about it, read Rick’s new book “Cane Toad Wars” (published by University of California Press, 2018). The book is written for the general public, not for scientists, and is aimed at a wide audience. The book can be purchased through Amazon or (within Australia) through Footprint Books. Or you can buy a copy through your local bookstore.