20170105-Mott-Thesis.pdf (6.45 MB)
Download fileYear-round movement and foraging ecology of frigatebirds, Fregata spp.
thesis
posted on 2017-01-10, 00:49 authored by Rowan William MottBiodiversity is
increasingly threatened as a result of intensifying anthropogenic activities.
To counter this decline there is an increasing recognition of the importance of
sound conservation management decision-making. The central tenet of this
process relies on scientific knowledge of the ecology and biology of the
systems in order to implement conservation measures with the highest efficacy.
In Section 1 of my thesis I undertook a structured literature review to
identify spatial patterns in existing research effort into the at-sea
distribution of seabirds. Of concern, this review highlighted many areas that
had received little research attention despite high seabird species richness or
exposure to high cumulative human impacts. Mismatches between the distribution
of research effort and areas of conservation importance will need to be
addressed and increasing international collaboration and facilitating uptake of
platforms of opportunity for vessel-based survey seem the most likely to
overcome current impediments. In marine systems, the large spatial extent,
dynamic nature, and financial and logistical constrains make collection of ecological
data difficult. Consequently, marine biologists often use indicator species to
provide information on marine condition and ecological processes. Accordingly,
Section 2 of my thesis examined the movements and foraging ecology of two
congeneric seabirds in a region identified in Section 1 as underrepresented in
the seabird spatial ecology literature. These species, Great Frigatebird
Fregata minor and Lesser Frigatebird F. ariel, possess adaptations unique among
seabirds that heighten their sensitivity to change in the marine environment.
In Section 2, resource partitioning between Great Frigatebirds and Lesser
Frigatebirds breeding at the same location primarily involved differences in
the type of prey consumed rather than spatial partitioning of foraging grounds.
Conversely, two populations of Lesser Frigatebirds breeding on separate, but
nearby, islands had stable isotope δ 13C values indicating differences in
location where prey was sourced. Prey availability differed markedly between
inshore locations favoured by one colony and offshore locations used by the
other colony. This disparity likely contributed to the large difference between
the reproductive outputs of the two colonies. For both inter- and intraspecific
partitioning cases, central place foraging constraints may have influenced the
observed patterns. Feather samples, which reflect non-breeding resource
acquisition, had a larger trophic niche width than samples reflecting breeding
season diet (red blood cells and plasma) suggesting increased variation in the
foraging strategy when not breeding. Data from GPS tracking devices identified
marine areas in south-east Asia as important locations for Great and Lesser
Frigatebirds that undertook a post-breeding dispersal. Habitat suitability
modelling using MaxEnt identified proximity to small (<1000 ha) islands as
the most important environmental predictor of habitat suitability for
non-breeding frigatebirds, with sea surface temperature also influencing
predicted habitat suitability to a lesser extent. Proximity to small islands is
a spatially static variable and, consequently, additions to the marine
protected area network informed by this habitat feature are likely to have more
predictable long-term benefits relative to those informed by dynamic features,
such as chlorophyll-α concentration. Together, these results demonstrate the
complex mechanisms used by tropical seabirds to partition foraging resources
and exploit their marine environment most effectively across time. They also
provide ecological insight that will be useful for conservation planning in the
eastern Indian Ocean and marine waters of southeast Asia.