State of NZ Garden Birds 2024 | Te Āhua o ngā Manu o te Kāri i Aotearoa
What are our garden birds telling us?
Birds act as backyard barometers – telling us about the health of the environment we live in. They are signalling significant changes in our environment over the last 10 years. We should be listening.
Manaaki Whenua – Landcare Research has distilled a substantial information base – bird counts gathered by New Zealanders from more than 49,000 garden surveys since 2014 – into simple but powerful metrics.
Thank you to all the citizen scientists who participated in the survey in 2024. It was a great turnout.
Key findings from the 2024 survey
Key signals continue for four native species:
- Kererū counts again show a shallow increase over 10 years (39%), but a shallow decline over 5 years (7%), with moderate to rapid declines seen in seven regions in the short term.
- Fantail (pīwakawaka) counts again show a shallow increase nationally over 10 years (43%), with moderate long-term increases in four regions. We now see little or no change in their counts over 5 years (2%), compared to the shallow increase seen last year.
- We continue to see a shallow increase in tūī (kōkō) counts in the long term (23%) and again in the short term (7%). Their regional long-term trends continue to show a rapid increase in Canterbury (207%) and now show a moderate increase in Marlborough (68%).
- Silvereye (tauhou) counts show little or no change nationally over 10 years (0%) and 5 years (2%), compared to the shallow and moderate declines, respectively, seen last year. Their regional long- or short-term trends now show increases in 10 regions.
Key signals for introduced species that also act as environmental indicators:
- Myna counts continue to show little or no change nationally over 10 years, but for the first time show a shallow decline (7%) over 5 years. There is some evidence that the rapid increase in their counts in Wellington continues in both the long and short term (237% and 82%, respectively).
- Goldfinch counts now show little or no change over 10 years (2%) and a moderate decline over 5 years (28%), compared to the short-term rapid decline seen last year.
- Starling, house sparrow, chaffinch, and dunnock counts again show a shallow decline over 10 years (14-18%). Starling counts show a shallow decline over 5 years (8%), while house sparrow and chaffinch show a moderate decline over 5 years (21% for both species).
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 2024 | Te āhua o ngā manu o te kāri i Aotearoa report.
What more needs to be done to care for birds?
Since 2021 we’ve asked New Zealand Garden Bird Survey participants what more needs to be done to care for the birds in Aotearoa New Zealand. In 2024, 4,652 participants responded to the question. We’ve analysed the responses, and they reflect the five themes below.
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.
Cleaning ‘noisy’ data
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.
