Action Synopsis: Bird Conservation About Actions

Provide supplementary food for parrots to increase reproductive success

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Two studies from New Zealand found some evidence that providing supplementary food for kakapos Strigopus habroptilus increased the number of breeding attempts made, whilst a third study found that birds provided with specially-formulated pellets appeared to have larger clutches than those fed on nuts.
  • One study found no evidence that providing food increased the number of nesting attempts.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A 1998 review of data from three islands in New Zealand between 1990 and 1997 (Clout & Merton 1998), found that providing kakapos Strigopus habroptilus with supplementary food (nuts, apples and sweet potatoes provided at feeding stations year-round) may have increased breeding attempts on Little Barrier Island, North Island, with no breeding attempts between 1982 (when 22 kakapos were translocated there) and 1989, but between two and four females nested in four of the next six years, following food provision. Male display behaviour also increased in this period. However, there were no similar increases on two other islands, with one of three females breeding once on Maud Island between 1991 and 1998, despite supplementary feeding from 1991 onwards. Females on Codfish Island only bred once between 1992 and 1998 (with a total of six females nesting), following supplementary feeding starting in 1992 and this coincided with heavy fruiting of rimu Dacrydium cupressinum trees. Overall breeding success was low across the study period, owing to high rates of egg fertility, and the starvation or probable predation of many chicks.

    Study and other actions tested
  2. A 2001 review of data from Little Barrier Island, North Island, New Zealand, between 1990 an 1999 (Elliott et al. 2001), using largely the same data as Clout & Merton 1998, found that female kakapos Strigopus habroptilus provided with supplementary food (nuts, apples and sweet potatoes provided at feeding stations year-round) bred significantly more frequently than females that did not take supplementary food (11 breeding attempts in 35 ‘bird years’ for fed birds vs. one breeding attempt in 82 ‘bird years’ for unfed birds). The authors note that the mechanism behind the relationship and that the response was extremely variable across other islands. A small analysis in the same study found that four fed females did not produce larger clutches than two unfed females (average of 2 eggs/clutch for both fed and unfed females). Neither of the unfed females raised young (and only one egg hatched), whereas a total of three chicks fledged from fed nests, but samples were too small to determine whether this difference was significant. Failure of both unfed nests was thought to be due to females spending large amounts of time away from the nest during incubation.

    Study and other actions tested
  3. A small study on Codfish and Pearl Islands, South Island, New Zealand, during 1997–2005 (Houston et al. 2007), found that kakapos Strigopus habroptilus fed with food pellets (specially formulated to provide nutrients missing from kakapos’ diets) laid larger clutches than those provided with either nuts (almonds, walnuts, Brazil nuts and honey-water) or no supplementary food (76% of 29 pellet fed birds having 3-4 eggs/clutch and an average of 2.76 eggs/clutch; 33% and 2.22 for nine nut-fed birds; 33% and 2.00 eggs/clutch for three unfed birds). However, fed birds did not nest more frequently than unfed birds, with nesting apparently related to the fruiting of rimu Dacrydium cupressinum trees. Food was either fed ad libitum or was 20 g of nuts every three days or 50-150 g of pellets every three days year-round.

    Study and other actions tested
Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2020) Bird Conservation. Pages 137-281 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.


Where has this evidence come from?

List of journals searched by synopsis

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Bird Conservation

This Action forms part of the Action Synopsis:

Bird Conservation
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