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2019 New Zealand Garden Bird Survey results
State of NZ Garden Birds 2019 | Te āhua o ngā manu o te kāri i Aotearoa
What are our birds telling us?The New Zealand Garden Bird Survey acts as the ‘canary in the coalmine’ for our nation’s common garden bird species. It helps us understand the health of garden bird populations and the wider environment by showing how bird counts are changing across Aotearoa over two time-frames – 5 and 10 years.
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Download State of NZ Garden Birds 2019 | Te āhua o ngā manu o te kāri i Aotearoa
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The latest results from the 2019 survey show positive signals for four native species. Increases of fantail (pīwakawaka), tūī and kererū counts have occurred over the last 10 years and accelerated in the last 5 years. While the moderate decline in silvereye (tauhou) counts is still apparent, this has slowed nationally in the last 5 years to 2%.
Things are not looking so positive for some introduced species. The results indicate shallow or moderate declines in bird counts for song thrush, goldfinch, starling and dunnock over the last 5 years. The National Picture provides more detail on changes for the bird species across Aotearoa.
Things are not looking so positive for some introduced species. The results indicate shallow or moderate declines in bird counts for song thrush, goldfinch, starling and dunnock over the last 5 years. The National Picture provides more detail on changes for the bird species across Aotearoa.
If you’re keen to know more about what’s happening with garden birds in your region, reports for individual regions are available, or check out out the full State of NZ Garden Birds 2019 | Te āhua o ngā manu o te kāri i Aotearoa report.
How we calculate NZ Garden Bird Survey results
The general idea behind the survey is to convert the individual bird counts people contribute into meaningful estimates of wider population changes over time. Counts from every garden surveyed are linked to their location within a neighbourhood, suburb, district and region to calculate how bird counts change over time at each of these spatial scales.
We expect a species whose population is increasing over time to show an increase in counts and vice versa. While this is simple in principle, because there are different numbers of gardens in different regions, and different people decide to participate in some years, it might appear as though bird count numbers have changed, when it is just the proportion or location of survey returns that have changed.
The type of garden surveyed (rural or urban), whether people feed birds, and the total number of gardens surveyed in a region also add complexity. Statisticians refer to this as ‘noisy data’ because there are so many variables to take into account.
To reduce this noise, we use cutting edge statistical techniques to account for these variables. Following bootstrap analysis and bias-correction of the modelled data, estimated trends in bird populations over the past 5- and 10-year periods are summarised nationally and regionally according to their direction (decline or increase) and size (rapid to shallow).
These long-term trends are called ‘signals’ and show a persistent increase or decrease in the abundance of a species. We categorise these signals in the following way:
We expect a species whose population is increasing over time to show an increase in counts and vice versa. While this is simple in principle, because there are different numbers of gardens in different regions, and different people decide to participate in some years, it might appear as though bird count numbers have changed, when it is just the proportion or location of survey returns that have changed.
The type of garden surveyed (rural or urban), whether people feed birds, and the total number of gardens surveyed in a region also add complexity. Statisticians refer to this as ‘noisy data’ because there are so many variables to take into account.
To reduce this noise, we use cutting edge statistical techniques to account for these variables. Following bootstrap analysis and bias-correction of the modelled data, estimated trends in bird populations over the past 5- and 10-year periods are summarised nationally and regionally according to their direction (decline or increase) and size (rapid to shallow).
These long-term trends are called ‘signals’ and show a persistent increase or decrease in the abundance of a species. We categorise these signals in the following way:
When using samples to estimate wider populations, we need some way of measuring whether the sample actually reflects the wider population. We used 80% confidence intervals for the average percentage change in each species’ counts to evaluate confidence in our estimates. We generally have more confidence at the regional level than district or suburb.
The easiest way to improve this confidence at the district or suburb level is to increase the number of bird counts done. The more people who participate, the greater the strength of our evidence for what’s happening to garden birds at the local scale.
For more information on the statistical techniques used please read our trend analysis methods report.
The easiest way to improve this confidence at the district or suburb level is to increase the number of bird counts done. The more people who participate, the greater the strength of our evidence for what’s happening to garden birds at the local scale.
For more information on the statistical techniques used please read our trend analysis methods report.
How have bird counts changed?
What's going on in your region?
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