**1. Introduction**

Global population trends show that humans are moving from rural areas into cities at a considerable rate, and once sparsely populated regions are being transformed to cope with the influx of people [1,2]. Subsequently, urbanisation is now widely considered a major threat to biodiversity conservation [3–5].

Species' responses to urbanisation can vary significantly [6]; however, prior to the 1990s, very few ecological studies were undertaken in urban areas due to them being considered unviable habitats for faunal populations and, ergo, immaterial from a conservation standpoint [7]. It is now shown that urban areas support an array of species that have been able to tolerate or adapt to the highly fragmented new environments but, due to a lack of appropriate knowledge, the success of urban conservation programmes may be hampered [4]. There is little doubt that avian assemblages are greatly altered by urbanisation; many bird species unable to adapt to the suddenly changed environment will often move out of an area resulting in diminished biodiversity and allowing invasive species to move in [4,8,9]. Other species can benefit from urbanisation; these are often

**Citation:** Fischer, S.E.; Edwards, A.C.; Weber, P.; Garnett, S.T.; Whiteside, T.G. The Bird Assemblage of the Darwin Region (Australia): What Is the Effect of Twenty Years of Increasing Urbanisation? *Diversity* **2021**, *13*, 294. https://doi.org/ 10.3390/d13070294

Academic Editor: Juan J. Morrone

Received: 30 April 2021 Accepted: 21 June 2021 Published: 28 June 2021

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birds with a more generalist diet and life-history traits that are conducive to living in a fragmented habitat [10].

Whilst studies of bird populations in urban areas abound in the temperate zones of both the Northern and Southern hemispheres, research into tropical urban avian communities is scant [11]. This trend is continued in Australian studies with the majority of research being undertaken in the temperate regions, predominantly in the two heavily populated states of New South Wales and Victoria. In contrast, this study is situated in the monsoonal tropics of northern Australia; specifically, in Darwin, the capital of the Northern Territory (NT). There has been targeted research on a range of species and thorough overviews of bird distributions within the region [12–14], with more detailed studies of shorebirds [15–18] and mangrove assemblages [19–21]. To date, however, there have been no studies of trends in terrestrial bird assemblages as the city has grown. Given the increased rate of urbanisation in the global tropics [22], coupled with high levels of biodiversity in the zone [11,23–25], there is an increasing need to gather data to better understand how bird communities are coping with the rising encroachment of human habitation. This is particularly interesting in Darwin as, unlike all other urban centres in Australia, Darwin has no introduced birds, so all the adaptation is being undertaken by native species as their environment is changed.

In the nearly 45 years since Darwin was severely damaged by Cyclone Tracy, where 70–80% of dwellings were destroyed [26,27], the city has grown from a perceived 'frontier town' to be a modern capital city. This development has seen an increase of over 20 new suburbs in the greater Darwin area and surrounds, and land once considered bush or rural properties is now being subdivided into urban blocks. One of the most common effects of urbanisation is the increasing prevalence of exotic species [28–30]; however, this has not occurred in the Darwin region with only four species listed as 'foreign invaders', none of which have established permanent breeding populations [31].

In this paper, we shall test this theory by investigating the response of the terrestrial avian assemblages in the Darwin region to urban expansion and land use change over the past 20 years.

#### **2. Materials and Methods**
