Action Synopsis: Bird Conservation About Actions

Reduce conflict by deterring birds from taking crops using bird scarers

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

Study locations

Key messages

  • A controlled paired study in the USA found reduced levels of damage to almond orchards when American crow Corvus brachyrhynchos distress calls were broadcast, compared to the previous year. There were no decreases in control orchards.
  • A replicated study in Pakistan found that four pest species were less abundant when reflector ribbons were hung above crops, compared to when ribbons were not used.


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 controlled, paired study in central California, USA (Houk et al. 2002), found that two of three almond orchards with crow distress calls broadcast had reduced damage from American crows Corvus brachyrhynchos in 2003, compared to 2002, when broadcasts were not used. Damage reduced from 6.0 kg/ha to 1.1 kg/ha, and 18.2 kg/ha to 4.8 kg/ha. There was no change in three paired sites without broadcasts. Orchards were 16-30 ha in area and monitored in June-August. Broadcasting units were deployed at onset of crow damage until almond harvest (1 unit/1.6 ha; hung in trees at 1-2 m) throughout the orchard, moved to a new tree every two weeks, switched to a different call every 3-4 days, broadcast dawn to dusk, each 25 seconds long with approximately 12 min between calls.

    Study and other actions tested
  2. A replicated two-month study (November-December) on agricultural land in Punjab, Pakistan (Hafeez et al. 2008), found that hanging reflector ribbons 65-100 cm above crops was a low cost technique that significantly decreased abundances of four main bird pest species (house crow Corvus splendens, ring-necked parakeet Psittacula krameri, common myna Acridotheres tristis and bank myna A. ginginianus) that heavily damage young wheat Triticum aestivum and maize Zea mays crops.

    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
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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.

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