Benefits of modelling abundance for rare species conservation: a case study with multiple birds across one million hectares

Aim: Many management programs that are based on the needs of rare or
threatened species are ineffective because they fail to collect enough
data to reliably estimate abundance and map distributions for their target
species. Information that does exist for rare species is often based on
presence-only data, because it is difficult to collect sufficient data on
abundance for such species. We targeted ten rare bird species that were
excluded from a recent study due to insufficient data. For these species,
we aimed to (a) collect sufficient abundance data, (b) identify important
locations and (c) estimate population sizes. Location: A large reserve
system (~1M-ha) in south-eastern Australia. Methods: We undertook
intensive field surveys, using repeat area searches of 660 independent
25-ha sites, totalling 2,640 hrs of surveys (2-hr surveys; two surveys per
site). We used N-mixture models to estimate abundance whilst accounting
for imperfect detection. Results: This survey effort returned enough
high-quality data on nine rare bird species to identify important
locations and estimate their population sizes. To illustrate potential
applications of mapped important locations, we used our results to assess
the likely impact of a planned burn program in part of the study region.
We identified planned burns that are likely to have a significant impact
on important locations for rare species that may not have otherwise been
identified. Populations were generally larger than previously estimated
using expert opinion. For example, our population estimate for the
threatened Red-lored Whistler (Pachycephala rufogularis) was ~16 times
larger than the previous estimate. Main Conclusions: Our results show (a)
the benefits of using abundance to identify important locations for rare
species (b) the value of developing bespoke survey methods for estimating
abundance of rare species with low detectability and (c) a pathway for the
application of mapped important locations in conservation land management.