Environmental Engineering Reference
In-Depth Information
week ofAugust and second week of September. Due to the staggered nature of
nesting, in both 2009/2010 and 2012/2013, three surveys would have been required
to detect all nests, if aerial surveys occurred at the optimum times.
Discussion
Aerial surveys are an effective method for detecting breeding nests and activity of
brolgas. In our 3 days of aerial surveys in 2009 and 2010 we were able to cover a
large area of potential brolga breeding habitat in a short period of time, detect or
confirm brolga nests, and determine the suitability of unattributed breeding sites for
follow-up ground truthing.
Approximately 800 km
2
were surveyed for potential brolga breeding habitat over
3 days. Aerial surveys allow for rapid identification of suitable breeding wetlands
and individual brolga nests, and are an effective method to survey large areas,
particularly when surveys are constrained by a limited breeding season. Surveying
for brolga nests over the same area from the ground required approximately twice
asmucheffort(100comparedwith200person-hours).Furthermore,groundsurveys
were limited to wetlands that could be observed from roads and tracks, while aerial
surveys covered the whole landscape. The ability to survey a large area relatively
quickly to detect brolga nests is important when other studies (e.g. brolga move-
ment and activity observations, home range surveys), are required once breeding
sites have been identified.
Aerial surveys also eliminate the sometimes difficult task of negotiating access to
largeareasofprivatelandpriortoknowingthehabitatontheproperty.Following
aerial surveys, specific landholders can be targeted for access based on brolga sight-
ings and suitable wetland habitat recorded during the lights.Aerial surveys also
provide an accurate representation of the spatial distribution of brolgas at a landscape
scale over a short time period. This is difficult, and much more time consuming, to
achieve from ground surveys alone.
At some nests brolgas were observed either sitting on, or in close proximity to,
thenestduringtheaerialsurveys.Forthesenests,ground-truthingwasonlycarried
out if follow-up investigation was required at the site (e.g. assessment of the stage
of breeding, number of eggs/chicks present, brolga behavioural studies). Where
individuals were not observed sitting on, or in the immediate vicinity of, the nest
during the aerial survey ground-truthing was undertaken to attribute each nest to a
species.
The primary objective of the aerial surveys was to identify brolga nests for
subsequent assessment and monitoring, rather than to estimate population size or
identify population trends, as has been undertaken as part of other aerial surveys for
cranespecies(e.g.Dreweinetal.
1996
;McCann
2001
; Motsumi et al.
2007
).Forthis
reason, our study did not consider the availability or detectability of cranes during
survey design. We assumed that detectability of active brolga nests during the aerial
surveys was 100 %, due to their large size, restricted nesting habitat and characteris-
