Citation: Babcock and Booth (2020) Using Canes to Deter Avian Predators. Tern Conservation Best Practice. Produced for “Improving the conservation prospects of the priority species roseate tern throughout its range in the UK and Ireland” LIFE14 NAT/UK/000394’
Last updated: October 2020
This is a live document we update regularly. If you have comments and suggestions, please email Chantal.Macleod-Nolan@rspb.org.uk
Last updated: October 2020
This is a live document we update regularly. If you have comments and suggestions, please email Chantal.Macleod-Nolan@rspb.org.uk
| Babcock and Booth (2020) Using Canes to Deter Avian Predators. Tern Conservation Best Practice. |
Key Messages
- Bamboo canes appear to be a simple and low-cost way to reduce large gull predation attempts on breeding terns in some cases, although there are few examples where sufficient monitoring has been done to assess effectiveness.
Information
Avian predators including large gull species (in the UK and Ireland: herring gull Larus argentatus, lesser black-backed gull Larus fuscus and great black-backed gull Larus marinus) and Eurasian kestrels Falco tinnunculus can have a significant detrimental impact on tern colonies through predation.
Kestrels most frequently target colonies of little terns Sternula albifrons, a Schedule 1 protected species under the Wildlife and Countryide Act 1981, and amber-listed in Birds of Conservation Concern 4 (Eaton et al. 2015). Yet kestrels are also a protected and declining species in the UK (Smart and Amar.2018) and are also amber listed, while herring gulls are red-listed and both lesser black-backed gull and great black-backed gull are amber-listed (Eaton et al. 2015).
Historically, culling or nest and egg destruction have been used to deter breeding gulls around tern colonies. Culling gulls more widely (to reduce noise, nuisance, pollution, damage to property, risk to aircraft, public health risks and impacts on other avian species) may have contributed to a decline in large gull numbers in the later part of the 20th century (Coulson, 2015). Although culling for conservation purposes represents a very small proportion of this, killing individuals of any species can be controversial especially for a conservation organisation, and non-lethal methods of reducing the impacts of predators are preferred wherever possible.
Managers at a number of tern colonies have therefore used bamboo canes in and around tern colonies with the intention of making access difficult for large gulls and creating a safe space for the smaller and more agile terns to nest. As yet there are limited data on the effectiveness of this method. If using canes, it is important to consider the safety of any staff or volunteers working within these areas e.g. provide eye protection.
Avian predators including large gull species (in the UK and Ireland: herring gull Larus argentatus, lesser black-backed gull Larus fuscus and great black-backed gull Larus marinus) and Eurasian kestrels Falco tinnunculus can have a significant detrimental impact on tern colonies through predation.
Kestrels most frequently target colonies of little terns Sternula albifrons, a Schedule 1 protected species under the Wildlife and Countryide Act 1981, and amber-listed in Birds of Conservation Concern 4 (Eaton et al. 2015). Yet kestrels are also a protected and declining species in the UK (Smart and Amar.2018) and are also amber listed, while herring gulls are red-listed and both lesser black-backed gull and great black-backed gull are amber-listed (Eaton et al. 2015).
Historically, culling or nest and egg destruction have been used to deter breeding gulls around tern colonies. Culling gulls more widely (to reduce noise, nuisance, pollution, damage to property, risk to aircraft, public health risks and impacts on other avian species) may have contributed to a decline in large gull numbers in the later part of the 20th century (Coulson, 2015). Although culling for conservation purposes represents a very small proportion of this, killing individuals of any species can be controversial especially for a conservation organisation, and non-lethal methods of reducing the impacts of predators are preferred wherever possible.
Managers at a number of tern colonies have therefore used bamboo canes in and around tern colonies with the intention of making access difficult for large gulls and creating a safe space for the smaller and more agile terns to nest. As yet there are limited data on the effectiveness of this method. If using canes, it is important to consider the safety of any staff or volunteers working within these areas e.g. provide eye protection.
Published Research
Canes have been used to reduce large gull predation on the Farne Islands, Northumberland, since 2002 but the effect was not measured until 2018 (Boothby et al. 2019). In this one-year replicated study, four areas of the Arctic tern breeding colony were each divided into three sections: no canes (control), low-density cane grid (c.2m apart) and high-density cane grid (c.1 m apart). The 1.5 m canes were inserted at an angle of 70° to the ground and large gull predation attempts were monitored daily during the 3-hour peak predation period.
The study found approximately half the number of large gull predation attempts were made in the caned areas compared to the control areas. High-density cane areas saw a greater effect than low-density areas but the difference was not statistically significant. Canes did not reduce the likelihood of a predation attempt succeeding.
The authors recognise that further research on whether gulls become habituated to the canes, whether gulls specialising in predating terns respond differently compared to generalist feeders, whether canes displace predation onto other species or populations, and what effect the use of canes may have on large gull population dynamics, would be valuable.
Canes have been used to reduce large gull predation on the Farne Islands, Northumberland, since 2002 but the effect was not measured until 2018 (Boothby et al. 2019). In this one-year replicated study, four areas of the Arctic tern breeding colony were each divided into three sections: no canes (control), low-density cane grid (c.2m apart) and high-density cane grid (c.1 m apart). The 1.5 m canes were inserted at an angle of 70° to the ground and large gull predation attempts were monitored daily during the 3-hour peak predation period.
The study found approximately half the number of large gull predation attempts were made in the caned areas compared to the control areas. High-density cane areas saw a greater effect than low-density areas but the difference was not statistically significant. Canes did not reduce the likelihood of a predation attempt succeeding.
The authors recognise that further research on whether gulls become habituated to the canes, whether gulls specialising in predating terns respond differently compared to generalist feeders, whether canes displace predation onto other species or populations, and what effect the use of canes may have on large gull population dynamics, would be valuable.
Case Studies
Port Edgar Marina Raft, Scotland: canes to deter large gulls from colonising a raft
Canes were added to the tern raft at Port Edgar Marina in the Firth of Forth prior to the 2019 breeding season with the aim of deterring gulls from colonising the raft.
Port Edgar Marina Raft, Scotland: canes to deter large gulls from colonising a raft
Canes were added to the tern raft at Port Edgar Marina in the Firth of Forth prior to the 2019 breeding season with the aim of deterring gulls from colonising the raft.
Figure 1. Port Edgar Marina tern raft canes at the start of the 2019 season (Chris Knowles)
Large gulls did not colonise the raft. There were no predation observations conducted at Port Edgar, but on regular monitoring visits no avian predation was seen or reported to the Forth Islands Tern Warden. One adult common tern Sterna hirundo was seen dead next to a broken cane on the 1st July following gusting winds and thunderstorms which may possibly have led to the bird colliding with a cane, but the cause of death was not investigated. Later in the summer a second cane was broken on the same side of the raft, but there was no carcass and the cause of the broken cane is not known (Knowles 2019).
Figure 2. View of the Port Edgar raft showing a broken cane and dead tern (Chris Knowles)
Dalkey Islands, Ireland: canes combined with other measures resulted in a good breeding season
Lamb Island is one of the Dalkey Islands, c.16 km/9.9 m south of Dublin and 3 km/1.9 m south of Dún Laoghaire harbour. A small tern colony has been present on the Dalkey complex for many years typically on Maiden Rock, the most northerly of the islands. Until three years ago, most of the terns breeding at the islands were common terns with 15-54 pairs recorded prior to 1988, but more recently Arctic terns Sterna paradisaea have been the most abundant tern species (Butler & Newton 2017). In May 2019, island staff set up a grid pattern of canes set at 1 x 1 m intervals and at a 45° angle with alternate rows pointing opposite directions (Figure 3) across a portion of Lamb Island. The idea being that 1m spacing is too close for large gulls (with a wingspan 1.25-1.7 m) to fit between, while terns which have wingspans less than 1 m can easily fly between them.
Lamb Island is one of the Dalkey Islands, c.16 km/9.9 m south of Dublin and 3 km/1.9 m south of Dún Laoghaire harbour. A small tern colony has been present on the Dalkey complex for many years typically on Maiden Rock, the most northerly of the islands. Until three years ago, most of the terns breeding at the islands were common terns with 15-54 pairs recorded prior to 1988, but more recently Arctic terns Sterna paradisaea have been the most abundant tern species (Butler & Newton 2017). In May 2019, island staff set up a grid pattern of canes set at 1 x 1 m intervals and at a 45° angle with alternate rows pointing opposite directions (Figure 3) across a portion of Lamb Island. The idea being that 1m spacing is too close for large gulls (with a wingspan 1.25-1.7 m) to fit between, while terns which have wingspans less than 1 m can easily fly between them.
Figure 3. Setting up the canes on Lamb Island (Tara Adcock)
Rat control measures also took place and there was vegetation left to shelter chicks. The tern breeding season in 2019 was considered successful on Lamb Island although the effectiveness of individual management measures cannot be separated. Trail cameras recorded a great black-backed gull and a peregrine falcon Falco peregrinus within the caned area, the latter predating an adult Arctic tern. Three nests were lost to predation at the egg stage, two of which were outside the canes, and one just inside the grid, but several nests outside the grid also fledged chicks (Adcock & Newton, 2019). The evidence for the effectiveness of canes is unclear in this case but it is intended to continue the use of canes on Lamb.
Coquet Island, NE England: discontinued use of canes around a Sandwich tern colony
On Coquet Island, canes were placed for several years around the edges of Sandwich tern Thalasseus sandvicensis colony. The Sandwich terns tend to nest in the northern-most vegetation management plots, furthest from the lighthouse. Being the closest tern plots to the large gull breeding areas these were therefore perceived as being potentially more exposed to large gull predation, as large gulls nest on the plateau beyond the plots, and there are often many loafing large gulls on the north end of the island.
The practice of putting out canes was discontinued because it was not thought to be effective, and additional chick shelters were provided instead. Additionally, the areas around the edge of the plot are left to grow long vegetation (much of it is nettle beds Urtica dioica) which the older chicks use as cover to hide when there is a threat.
On Coquet Island, canes were placed for several years around the edges of Sandwich tern Thalasseus sandvicensis colony. The Sandwich terns tend to nest in the northern-most vegetation management plots, furthest from the lighthouse. Being the closest tern plots to the large gull breeding areas these were therefore perceived as being potentially more exposed to large gull predation, as large gulls nest on the plateau beyond the plots, and there are often many loafing large gulls on the north end of the island.
The practice of putting out canes was discontinued because it was not thought to be effective, and additional chick shelters were provided instead. Additionally, the areas around the edge of the plot are left to grow long vegetation (much of it is nettle beds Urtica dioica) which the older chicks use as cover to hide when there is a threat.
Figure 4. Sandwich tern breeding plot on Coquet Island showing canes which were once used around the edges to discourage large gulls. (Paul Morrison; RSPB)
Eccles, E England: canes to deter kestrel predation of little tern chicks
In 2019, canes were trialled as a method of deterring kestrel predation of little tern chicks. Short canes, between 0.5 m and 1 m long, were deployed in areas of marram grass Ammophila arenaria where little tern chicks seek shelter after hatching from nests in areas of open sand and shingle. The canes were pushed into the sand at a variety of spacings and angles so that no pattern would be apparent. Canes were not used in open sandy areas (where chick shelters are provided) since the chicks didn’t stay in these areas for long and it wasn’t practical to deploy canes throughout the whole area.
In 2019, canes were trialled as a method of deterring kestrel predation of little tern chicks. Short canes, between 0.5 m and 1 m long, were deployed in areas of marram grass Ammophila arenaria where little tern chicks seek shelter after hatching from nests in areas of open sand and shingle. The canes were pushed into the sand at a variety of spacings and angles so that no pattern would be apparent. Canes were not used in open sandy areas (where chick shelters are provided) since the chicks didn’t stay in these areas for long and it wasn’t practical to deploy canes throughout the whole area.
Figure 5. Short canes at Eccles little tern colony to deter kestrel predation (RSPB)
The canes were deployed part way through the breeding season once kestrels had shown an interest in the site. It appears that 2019 was a good year for small mammals in this area as generally kestrel predation at the site was low. No structured observations of predation attempts in the caned and un-caned areas of marram grass were conducted, but it was suggested by observers that kestrels might be avoiding the caned areas. It is intended to use canes again in 2020.
References
Adcock, T. and Newton, S. (2019) Dalkey Islands Tern Report 2019. BirdWatch Ireland Seabird Conservation Report
Boothby, C., Redfern, C. and Schroeder, J. (2019) An evaluation of canes as a management technique to reduce predation by gulls of ground‐nesting seabirds. Ibis, 161: 453-458.
Butler, A. and Newton, S.F. (2018) Dalkey Islands Tern Report 2017. BirdWatch Ireland Seabird Conservation Report
Coulson, J. C. (2015) Re-evaluation of the role of landfills and culling in the historic changes in the Herring Gull (Larus argentatus) population in Great Britain. Waterbirds 38: 339–354.
Eaton MA, Aebischer NJ, Brown AF, Hearn RD, Lock L, Musgrove AJ, Noble DG, Stroud DA and Gregory RD (2015) Birds of Conservation Concern 4: the population status of birds in the United Kingdom, Channel Islands and Isle of Man. British Birds 108, 708–746.
Knowles, C. (2019) Forth Islands Tern Warden Season Report 2019. Unpublished report.
Smart, J. & Amar, A. (2018) Diversionary feeding as a means of reducing raptor predation at seabird breeding colonies. Journal for Nature Conservation, 46, 48‐55.
Acknowledgements
Thanks to Caroline Spinks (RSPB volunteer at Eccles and Winterton).
Adcock, T. and Newton, S. (2019) Dalkey Islands Tern Report 2019. BirdWatch Ireland Seabird Conservation Report
Boothby, C., Redfern, C. and Schroeder, J. (2019) An evaluation of canes as a management technique to reduce predation by gulls of ground‐nesting seabirds. Ibis, 161: 453-458.
Butler, A. and Newton, S.F. (2018) Dalkey Islands Tern Report 2017. BirdWatch Ireland Seabird Conservation Report
Coulson, J. C. (2015) Re-evaluation of the role of landfills and culling in the historic changes in the Herring Gull (Larus argentatus) population in Great Britain. Waterbirds 38: 339–354.
Eaton MA, Aebischer NJ, Brown AF, Hearn RD, Lock L, Musgrove AJ, Noble DG, Stroud DA and Gregory RD (2015) Birds of Conservation Concern 4: the population status of birds in the United Kingdom, Channel Islands and Isle of Man. British Birds 108, 708–746.
Knowles, C. (2019) Forth Islands Tern Warden Season Report 2019. Unpublished report.
Smart, J. & Amar, A. (2018) Diversionary feeding as a means of reducing raptor predation at seabird breeding colonies. Journal for Nature Conservation, 46, 48‐55.
Acknowledgements
Thanks to Caroline Spinks (RSPB volunteer at Eccles and Winterton).