Bird population trends
The primary aim of the garden bird survey is to monitor long-term trends in common garden bird populations. The survey has been running for only 7 years, not a long time compared with 35 years that the Big Garden Bird Watch has been running in the UK, but some trends are starting to appear.
Perhaps the most encouraging trends are increases in counts of native tui and fantail (see accompanying graphs). It is too soon to determine whether these increases are part of a longer-term trend or just part of normal fluctuations in numbers over time. Counts of other native species such as silvereye, bellbird, kereru, and grey warbler have not increased over the last 7 years, but have not declined either. Their numbers have fluctuated from year to year, presumably in response to factors such as weather, food supply, predation, and disease. Why tui and fantail have increased but not other species such as bellbird and grey warbler is unclear. Counts in years to come may clarify the situation (see below).
Counts of two introduced bird species, house sparrow and eastern rosella, increased from 2007 to 2013, but counts of two others, blackbird and song thrush, declined. Counts of most other introduced species did not change significantly over the 7 years.
The results reported here should be interpreted with caution because 7 years is not a long time and the 2014 counts could change current trends. For example, if the tui count in 2014 is lower than it was in 2013, as it was in 2012 (which is conceivable), then there would be no linear trend from 2007 to 2014. However, if it was higher than it was in 2013 (which is also conceivable) then the current linear increase in tui counts would continue. Thus, the trends reported here are the trends observed from 2007 to 2013. Longer-term trends may be different. Trends may also be different in different regions of the country, and this is currently being investigated.
The survey is unable to identify the causes of changes in bird population trends, but can alert us of the need to investigate them (e.g. are they caused by a change in predator numbers, disease status, habitat condition, or some other factor?). Changes in bird populations that might cause concern include downward trends of native species such as tui and bellbird, and upward trends of adventives such as myna and eastern rosella.
Top 10 species
House sparrow was once again the most numerous species counted in our gardens nationally. It was also the most numerous species counted in gardens in the UK in 2013 (see www.rspb.org.uk/birdwatch/). The second most numerous, and most numerous native species, was again silvereye. These two species are by far the most commonly counted in our gardens.
Table of the top 10 birds in 2013 nationally and in the five main regions (average number per garden). National averages were calculated from 16 regional averages weighted by the regional proportions of households.
Counts of different species varied in different regions of the country. For example, house sparrow was much more numerous in Auckland than in Otago, while silvereye was much more numerous in Otago than in Auckland. Tui was fifth most numerous species (and second most numerous native species) nationally but was rare in Canterbury. The introduced myna was sixth most numerous nationally and third most numerous in Auckland but wasn’t recorded south of Wellington. Bellbird, the 17th most numerous species nationally (not shown in the table above), was the fifth most numerous in Southland and Otago but did not occur in the top 10 (or even top 20) in Auckland and Northland. See National average counts of the 31 most numerous species for more information.
As well as varying between regions, counts varied between urban and rural gardens, and between gardens with and without the provision of supplementary food (see previous reports).
Number of species detected
A total of 75 species of birds was detected in (or from) gardens in 2013, the lowest since the survey began. Of these, 44 species were detected in (or from) fewer than 35 gardens (less than 1% of gardens), some from just one garden; Australasian gannet, black shag, little shag, pied shag, spotted shag, reef heron, cattle egret, black swan, mute swan, Canada goose, greylag goose, grey duck, scaup, royal spoonbill, falcon, common pheasant, California quail, brown quail, peafowl, helmeted guinea fowl, weka, SI pied oystercatcher, variable oystercatcher, pied stilt, Pacific golden plover, black-billed gull, Caspian tern, white-fronted tern, Barbary dove, kaka, red-crowned parakeet, crimson rosella, shining cuckoo, morepork, kookaburra, pipit, skylark, rifleman, fernbird, whitehead, robin, tomtit, stitchbird, and redpoll. That leaves 31 species detected in (or from) more than 1% of gardens.
Number of survey returns
(Excludes returns from schools, parks, and other locations)
|Year||Number||% entered online|
The total number of survey returns this year was slightly lower than last year. Most returns came from Wellington (23%), followed by Auckland (19%), Canterbury (16%), and Otago (13%). Otago contributed the most survey returns on a per household basis (13% of returns from 5% of national households) and Auckland the fewest (19% of returns from 30% of national households). Other regions contributing ‘above their weight’ included Wellington (23% of returns from 11% of national households) and Marlborough (2% of returns from 1% of national households).
Survey forms were published by the Dominion Post (Wellington), The Press (Christchurch), and Otago Daily Times (Dunedin), as well as by Forest & Bird and Southern Bird magazines. Of all returns, 70% were entered directly online by participants and 30% by volunteer data-entry operators. The online survey form was developed by Andy Ball from Fairfax Media, and was accessible from the Dominion Post, Landcare Research, Forest & Bird, and Ornithological Society websites (and maybe others). Of the hardcopy survey returns entered by volunteers, most were from the form published in the Dominion Post newspaper.
Table showing source of garden bird survey returns received in 2013
|Source||Number received||% received||% hardcopy|
|Online data-entry by participants||2462||70.1||-|
|Newspaper form from Dominion Post||283||8.1||27.0|
|Paper form handed out to public (9,900)||212||6.0||20.2|
|Paper form printed from website||173||4.9||16.5|
|Newspaper form from The Press||140||4.0||13.3|
|Newspaper form from Otago Daily Times||110||3.1||10.5|
|Forest & Bird magazine form (14,000)||110||3.1||10.5|
|Southern Bird magazine form (1,000)||9||0.3||0.9|
|Other sources (e.g. letter, email)||12||0.3||1.0|
Number of birds counted
138,423 birds (average 39.4 birds per garden)
This survey was possible only thanks to the large number of volunteer participants who counted birds in their gardens. Thanks also to Landcare Research for promoting the survey, funding printing of the survey form, and providing programmer and webmaster support; Forest & Bird, Ornithological Society, newspaper, radio, and television companies for promoting the survey; A. Ball, Fairfax Media, for designing the online survey form; about 30 volunteers for helping enter the data from hardcopy survey forms into the computer; and Topflite® bird feeds for sponsorship.