Action: Use signs and access restrictions to reduce disturbance at nest sites
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- Six studies (two replicated and controlled, two before-and-after and two small studies) from across the world found increased numbers of breeders, higher reproductive success or lower levels of disturbance in waders and terns following the start of access restrictions or the erection of signs near nesting areas. One Canadian study involved the use of multiple interventions.
- A before-and-after study from the USA found that a colony of black-crowned night herons Nycticorax nycticorax was successfully relocated to an area with no public access.
- One small study from Europe and one replicated and controlled study from Antarctica found no effect of access restrictions on the reproductive success of eagles or penguins, respectively.
If most disturbance to nesting birds is accidental, then simply warning the public that there are birds present, or restricting access at certain times of the year may help reduce disturbance and the abandonment or destruction of nests. Conversely, if disturbance is coming from people attempting to see nests or birds, then alerting the public to their presence with signs could be counter-productive.
Supporting evidence from individual studies
A small study in 1976-88 in the wetlands of the Doñana National Park, Andalucia, Spain (Ferrer & Hiraldo 1991), found that there were no differences in number of Spanish imperial eagle Aquila adalberti pairs that laid, clutch size, hatching size or nestling survival after trails near nests were temporarily closed. This study discusses other eagle management techniques, described in ‘Add perches to electricity pylons to reduce electrocution’, ‘Bury or isolate power lines’, ‘Foster eggs or chicks with wild conspecifics’ and ‘Remove/treat endoparasites’.
Two before-and-after studies in 1977-89 at two common tern Sterna hirundo colonies in Lake Ontario, Canada (Morris et al. 1992), found that the nesting population increased at one colony but decreased at the second following the use of several interventions, including the erection of signs highlighting the presence of nesting birds. This study is discussed in ‘Replace nesting substrate following severe weather’.
A replicated controlled study on a 28 km stretch of coast in a heavily-visited national park in Victoria, Australia (Dowling & Weston 1999), found that hooded plovers Thinornis rubricollis had significantly higher reproductive success in 1991-8 under three restricted-access regimes, compared to two regimes that allowed dogs on the beach (0.55 fledglings/clutch for 40 restricted access clutches vs. 0.10 fledglings/clutch for 131 open-access clutches). Hatching success was 31-40% and fledging success 31-68% for the 40 clutches in areas with no access for dogs; both dogs and people or under a ‘Plover Watch’ scheme, where volunteers ask people to avoid nests and control dogs. This compared with hatching and fledging success of 0-12% and 0-16% for 131 clutches in areas where dogs were prohibited from 0900–1700 each day or where there was unrestricted access to people and dogs. Overall, the average number of fledglings increased over the study period.
A replicated, controlled study on Goudier Island (2 ha), Antarctica (Cobley & Shears 1999), in the austral summer of 1996-7, found that gentoo penguins Pygoscelis papua did not have significantly higher reproductive success at colonies with no access by tourists, compared to six colonies that tourists could walk through. The percentage of birds laying and eggs hatching did not vary between colonies (82-98% of birds laying and 71-95% of eggs hatching for 556 nests in disturbed colonies vs. 89-100% laying and 88-90% hatching for 170 nests in control colonies), nor did the growth rates of chicks. Overall, 3,103 tourists visited the island making a total of 7,938 ‘man-hours’ of visits over four months. Tourists could walk under supervision through six disturbed colonies but could not approach closer than 25 m to four protected colonies (with two 70 m away and partially concealed by rocks).
A before-and-after trial from July-August in 1997-1998 in the waterways surrounding a common tern Sterna hirundo nesting island in Barnegat Bay, USA (Burger & Leonard 2000), found that disturbance and reproductive costs caused by personal watercraft disturbance significantly decreased after the implementation of educational campaigns and increased signage in late 1997. This study is discussed in ‘Start educational programs for personal watercraft owners’.
A before-and-after trial at a coastal site in Long Beach, California, USA (Crouch et al. 2002), reported the successful translocation of a black-crowned night heron Nycticorax nycticorax colony to a site where public access was stopped. This study is discussed in ‘Translocate individuals’.
A replicated before-and-after study in 1982, 1987, 1992 and 2002 at 17 local beaches within Delaware Bay, USA (Burger et al. 2004) found that disturbance to shorebirds decreased markedly following intensive management intervention to control birdwatchers and crab collectors. Both the mean disruption rate and the mean time that shorebirds were disturbed increased during the 1980s when there were no restrictions or viewing platforms and then declined by 2002 after viewing platforms were constructed and beach access restrictions were enforced (5.6 disruptions/hour and 53 minutes disturbed/hour in 1987 vs. 0.4 and 3.6 in 2002). Fewer people were observed on the beaches after restrictions were enforced and only one bird watcher disturbed the birds in 2002. However, the percentage of disturbed shorebirds that flew away (and did not return within 10 min) did not change during the 1980s and increased in 2002. Observations were made on 12–20 days each year for 6–10 h per day.
A small before-and-after study on a beach in California, USA (Lafferty et al. 2006), found that the number of breeding snowy plovers Charadrius alexandrinus increased from one pair in 2001 to 26 pairs (fledging 74 young) in 2004, following the installation of a simple rope fence in June 2001. The probability of eggs being trampled in 2002 was 8% outside the roped area, compared with 0% inside. The fence consisted of metal posts every 5 m and a single rope strung across the top. In 2001, 265 m of beach was roped off; this increased to 400 m in 2002 and further increased in 2003-4.
A replicated, controlled study at three sandy beaches in Algarve, Portugal (Medeiros et al. 2007), found that little tern Sterna albifrons breeding success in 2003-5 was significantly higher on two beaches with information and warning signs and weekend wardening, compared to a beach without protective measures (50-91% nesting success for 339 nests on the two protected beaches vs. 0-35% success for 153 nests on the unprotected beach). The presence/absence of protective measures was the most important predictor of nesting success. The main causes of nest failure were predation, destruction by humans and dogs and abandonment.
A small study in Victoria, Australia, between 2003 and 2007 (Weston et al. 2008) found that two hooded plover Thinornis rubricollis nests located on beaches that were being cleaned following an oil spill, both survived and fledged young, after they were marked using signs and rope fences. In addition, cleaning crews worked for 20 minutes and then stopped for 20 minutes to allow adults to incubate the eggs. This study is also discussed in ‘Clean birds following oil spills’.
- Ferrer M. & Hiraldo F. (1991) Evaluation of management techniques for the Spanish imperial eagle. Wildlife Society Bulletin, 19, 436-442
- Morris R.D., Blokpoel H. & Tessier G.D. (1992) Management efforts for the conservation of common tern Sterna hirundo colonies in the Great Lakes: two case histories. Biological Conservation, 60, 7-14
- Dowling B. & Weston M.A. (1999) Managing a breeding population of the hooded plover Thinornis rubricollis in a high-use recreational environment. Bird Conservation International, 9, 255-270
- Cobley N.D. & Shears J.R. (1999) Breeding performance of gentoo penguins (Pygoscelis papua) at a colony exposed to high levels of human disturbance. Polar Biology, 21, 355-360
- Burger J. & Leonard J. (2000) Conflict resolution in coastal waters: the case of personal watercraft. Marine Policy, 24, 61-67
- Crouch S., Paquette C. & Vilas D. (2002) Relocation of a large black-crowned night heron colony in southern California. Waterbirds, 25, 474-478
- Burger J., Jeitner C., Clark K. & N L.J. (2004) The effect of human activities on migrant shorebirds: successful adaptive management. Environmental Conservation, 31, 283-288
- Lafferty K., Goodman D. & Sandoval C. (2006) Restoration of breeding by snowy plovers following protection from disturbance. Biodiversity and Conservation, 15, 2217-2230
- Medeiros R., Ramos J.A., Paiva V.H., Almeida A., Pedro P. & Antunes S. (2007) Signage reduces the impact of human disturbance on little tern nesting success in Portugal. Biological Conservation, 135, 99-106
- Weston M.A., Dann P., Jessop R., Fallaw J., Dakin R. & Ball D. (2008) Can oiled shorebirds and their nests and eggs be successfully rehabilitated? A case study involving the threatened hooded plover Thinornis rubricollis in south-eastern Australia. Waterbirds, 31, 127-132