Protect nests and nesting sites from predation using chemical deterrents

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Four studies evaluated the effects of protecting nests and nesting sites from predation using chemical deterrents on reptile populations. Two studies were in the USA and one was in each of Spain and Australia.



  • Reproductive success (4 studies): Three of four controlled studies (including three replicated studies) in Spain, the USA and Australia found that a similar number of artificial Hermann’s tortoise nests, diamondback terrapin nests and loggerhead turtle nests that had chemical deterrents, pepper powder or chilli powder applied were predated compared to nests with no deterrent. The other study found that fewer loggerhead turtle nets that had habanero pepper powder applied to the surface were predated than nests with no pepper powder, or nest with pepper powder below the surface.


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 study in 2006 in grasslands in Catalonia, Spain (Vilardell et al. 2008) found that chemical deterrents did not prevent artificial Hermann’s tortoise Testudo hermanni nests from being predated. Results were not statistically tested. Almost all artificial Hermann’s tortoise nests were predated within four days whether they were protected with chemical repellent (carnivore repellent: 63 of 64, 98% nests predated, carnivore and wild boar Sus scrofa repellent: 78 of 80, 98%) or not (143 of 144, 99% nests predated). Unprotected nests were generally predated more quickly than protected nests. Wild boar predated 85% of nests when wild boar and carnivore repellent were used together compared to 99% of nests when carnivore repellent only was used. Other predators included common genet Genetta genetta, beech marten Martes foina and fox Vulpes vulpes. Artificial nests (three quail Coturnix coturnix eggs, buried and watered with 15 ml of diluted tortoise urine and excrement) were created in eight plots (625 m2/plot) in a Hermann’s tortoise breeding colony. In June 2006, Schwelger© carnivore repellent was distributed in four plots (25 devices/plot; 16 nests/plot). In September 2006, wild boar repellent (Stop Jabali © Hagopur GmbH) and fresh carnivore repellent were distributed to the same four plots (20 nests/plot). Nests in experimental and untreated plots were checked for predation daily for the first 15 days and weekly for up to 3 months.

    Study and other actions tested
  2. A replicated, controlled study in 2010 on a sandy beach in  South Carolina, USA (Lamarre-DeJesus & Griffin 2013) found that using habanero pepper Capsicum chinense powder to cover the surface of loggerhead turtle Caretta caretta nests resulted in reduced predation by coyotes Canis latrans compared to nests with pepper powder under the surface and nests with no pepper powder. The number of predated nests was lower for surface pepper treated nests (2 of 10, 20%) compared to nests with pepper under the surface of the sand (5 of 10, 50%) and nests with no pepper (6 of 10, 60%). A similar number of surface pepper treated nests were predated compared to nests covered with a screen (7 of 33, 21%). Nests were covered with 15 ml of habanero pepper powder on the surface of the nest (10 nests), below the surface and 3 cm above the eggs (10 nests) or were given no pepper powder (10 nests). A further 33 nests were covered with a plastic or metal screen (1 x 1 m). In June–July 2010, nests were monitored for complete or partial predation every 1–3 days, and a further 12 visits were made until September.

    Study and other actions tested
  3. A replicated, controlled study in 2014 in one brackish wetland in New York, USA (Burke et al. 2015) found that applying habanero pepper Capsicum chinense powder to diamondback terrapin Malaclemys terrapin nests did not decrease predation compared to nests with no pepper powder. The number of predated nests was similar for those covered with pepper powder (10 g pepper: 15 of 15, 100%; 20 g pepper: 14 of 15, 93%) and those with no pepper powder (15 of 18, 83%) (statistical significance not assessed). The number of days until predation was also not affected by pepper treatment (10 g pepper: 1.3 days; 20 g pepper: 1.8 days) or no pepper (1.4 days). In addition, nests covered with pepper and a mesh cage had similar hatching success to nests covered with just a mesh cage (all doses of pepper: 78–83%; no pepper: 55–93%). In June–July, 30 nests were covered with habanero pepper powder (10 g: 15 nests; 20 g: 15 nests) and 18 nests received no pepper powder. A further two nests received 10 g of pepper and were covered with a metal mesh cage (buried 15 cm deep), and nine were covered with cages but received no pepper. All nests were monitored daily: uncaged nests for a minimum of seven days, and caged nests until mid-November, at which point they were excavated to determine hatching success.

    Study and other actions tested
  4. A replicated, controlled study in 2014–2016 at one beach in south-eastern Queensland, Australia (Lei & Booth 2017) found that applying hot chilli pepper over loggerhead turtle Caretta caretta nests did not reduce nest predation. The number of predated nests did not differ significantly between those with chilli powder and those without chilli in 2014–2015 (chilli: 6 of 10, 60%; no chilli: 10 of 11, 91%) and 2015–2016 (chilli: 6 of 15, 40%; no chilli: 2 of 16, 13%). Yellow-spotted goannas Varanus panoptes were the most common predator of nests. In May 2014–June 2015, ten nests each had 40 g of hot chilli powder applied to a 0.5 x 0.5 m area over the top at a depth of 10–20 cm and a further 11 nests had no chilli applied. In 2015–2016 (months not stated), 15 nests had chilli applied and 16 nests had no chilli applied. Each nest was visited daily in early December–February 2014–2016 to record predation events.

    Study and other actions tested
Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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