Action Synopsis: Bird Conservation About Actions

Provide supplementary food for rails and coots to increase reproductive success

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

Study locations

Key messages

  • A small randomised and controlled trial in the USA found that fed American coots Fulica americana laid heavier eggs, but not larger clutches than controls.
  • However, a randomised, replicated and controlled study in Canada found that clutch size, but not egg size was larger in fed American coot territories. There was also less variation in clutch size between fed territories.
  • The Canadian study also found that coots laid earlier when fed, whilst a replicated cross-over trial from the UK found three was a shorter interval between  common moorhens Gallinula chloropus clutches in fed territories, but that fed birds were no more likely to produce second broods.


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 small randomised and controlled trial on a lake in Washington State, USA, in 1982 (Hill 1988), found that American coots Fulica americana from three territories given supplementary food (1 kg of dog food provided three times a week in each experimental territory) laid heavier eggs than coots from four control (unfed) territories (30 g/egg for fed birds vs. 28 g/egg for controls), but that there was no consistent effect on clutch size (first laid clutches: 8 eggs/clutch for fed territories vs. 9 eggs/clutch for controls; when including replacement clutched: 8.7 eggs/clutch vs. 9.0 eggs/clutch).

    Study and other actions tested
  2. A replicated cross-over trial in a waterfowl park in Cambridgeshire, UK (Eden et al. 1989), during spring and summer 1986 and 1987 found that common moorhens Gallinula chloropus had less time between clutches when provided with supplementary food than when no food was provided (average of 43 days between broods when fed vs. 49.0 days when unfed, nine females tested). However, fed birds were not more likely to produce second broods (84% of 19 fed territories producing second broods vs. 70% of 44 controls). Supplementary food was provided by an ‘igloo-shaped feeder’ in each fed territory, from five days before the first clutch hatched until the second clutch (if produced) was completed.

    Study and other actions tested
  3. A randomised, replicated and controlled study in wetlands in Manitoba, Canada, in 1987-9 (Arnold 1991), found that within-clutch variation in the size of American coot Fulica americana eggs was slightly (and significantly) lower in territories where supplementary food was provided (at least one of steam- rolled corn, commercial trout food, commercial rabbit, chicken layer diet or oystershell), compared to in control (unfed) territories (3,219 eggs from 357 clutches measured, standard deviation of 1.2 cm3 for fed clutches vs. 1.4 cm3 for controls). Additional results from this study are presented in Arnold 1994.

    Study and other actions tested
  4. A randomised, replicated and controlled study in wetlands in Manitoba, Canada, in 1987-9 and 1991 (Arnold 1994), found that American coots Fulica americana laid clutches significantly earlier and had significantly larger clutches when provided with supplementary food (steam-rolled corn and commercial rabbit food), compared with control (unfed) pairs (average of May 5th for first laying date for fed 309 pairs vs. May 7th for 386 unfed pairs). However supplementary food did not affect egg size or laying rate and the authors note that feeding only accounted for 1% and 3% of the variation in laying date and clutch size respectively. No data was presented on the hatching rate or survival of chicks.

    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

All the journals searched for all synopses

Bird Conservation

This Action forms part of the Action Synopsis:

Bird Conservation
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust