Bird Diversity and Habitat Project Overview

 

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Principle Investigators

Sandy Gilmore (ANU)

Brendan Mackey (ANU, CRCGA)

 

 

Introduction

 

The bird diversity project was developed in 2004 as a way to extend the landscape dynamics research to fauna, as this was a gap in the current research program.  Previous research had identified a link between above ground woody biomass and bird diversity therefore the aim of this project was to see if this also occurred in the open forests and woodlands of the study area, located in the northern Brigalow Belt bioregion.

 

 

Methods

 

Population densities of birds in the upper Maranoa catchment were estimated at 65 woodland or open forest sites, across a range of soils and terrain types.  Of the 65 sites, 59 were not recent regrowth or ring barked stands, though cattle grazing occurred in almost all sites, and some areas had been selectively logged for Callitris species in the past.  The survey was undertaken over 2 weeks in June 2004.

 

At each site bird population densities were estimated using a variable distance count method (Reynolds et al.  1980), where the distance to each individual bird is estimated in 20 minute blocks.  Some sites were repeatedly sampled. 

 

 

Results

 

Fifty six species were recorded with most only occupying a few sites, with many apparently suitable sites unoccupied and a noticeable lack of bark feeders.  The species found where made up of:

-          12 grain feeders,

-          1 fruit feeder,

-          1 pollen/nectar feeder,

-          1 carnivore,

-          13 large and 28 small insect feeder or omnivorous species.

 

 

Of the 65 sites, the texture of the topsoil was mainly sandy on 28 sites, mainly clay, sometimes with rock on 16, and loamy or duplex (multiple layers of different soil types) on 21 sites.

 

 

Major Findings

 

Individual species typically increased in densities in linear proportion to average food availability per species and soil carbon content (see Figure 1), but not above ground biomass nor structural complexity (see Figure 2).  However these factors may be important within a floristic productivity class.

 

Figure 1: Examples of two bird species showing the relative area they are found within and the estimated energy consumption per broad soil type.

 

 

Figure 2:  Structurally complex (i.e. relatively undisturbed) forests on clay soils like the site shown here, but with less above ground woody biomass than other sites in the area, supported the greatest bird diversity.

 

 

There was a linear relationship between insectivore species richness, total densities, total energy consumed and an index of tree foliage nutrient content.

 

There was an associated pattern of fewer bird species as one travels along a gradient of declining food productivity and insect richness, although this was not absolute.  With the exception of Noisy Miners (see Figure 3), and other widespread typically larger species, the highest densities and diversity are found on the most nutrient rich (generally clay) soils (see Figure 4). 

 

Figure 3:  Noisy Miners are widespread, and tend to force other small birds away when they are present, due to aggressive territorial behaviour

 

Figure 4.  Increasing species richness was found when there was more clay in the soil

 

 

Within this climatically homogeneous region the site variation in carrying capacities of all herbivores (cattle, kangaroos or insects) appear to be substantially controlled by nutrient constraints.  The vegetation growing on the sandy soils that support a low nutrient flora (but often higher above ground woody biomass) remains substantially uncleared, but is of minimal use as a basis for conserving declining woodland bird species, despite its importance for other components of the biota.

 

 

Further Information

 

Sandy Gilmore

Research Fellow

School of Resources, Environment and Society (SRES)

Australian National University

Acton

A.C.T. 0200

 

ph: +61 (2) 6125 4417

email: <sandy.gilmore@anu.edu.au>

 

 

Gilmore, A. M. (2004) Energy optimization links forest productivity to assemblage structure, species diversity and niche evolution in a guild of ground foraging birds.  PhD thesis, Southern Cross University, Lismore Australia

 

 

References

 

Reynolds, R.T., Scott, J.M., and Nussbaum, R.A. (1980). A variable circular-plot method for estimating bird numbers. Condor 82: pp 309-313

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bustards (or plains turkey) are rather large birds found in the open grassy areas of the study area