Effects of colony relocation on diet and productivity of Caspian terns

Published source details Roby D.D., Collis K., Lyons D.E., Craig D.P., Adkins J.Y. & Myers A.M. (2002) Effects of colony relocation on diet and productivity of Caspian terns. Journal of Wildlife Management, 66, 662-673.
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This study is summarised as evidence for the following.

	Action	Category
	Alter habitat to encourage birds to leave an area Action Link
	Move fish-eating birds to reduce conflict with fishermen Action Link
	Remove vegetation to create nesting areas Action Link
	Control avian predators on islands Action Link
	Use vocalisations to attract birds to safe areas Action Link
	Use decoys to attract birds to safe areas Action Link

Alter habitat to encourage birds to leave an area

A before-and-after study on two small islands in the Columbia River Estuary, Oregon, USA (Roby et al. 2002), found that an entire Caspian tern Sterna caspia colony (approximately 8,900 pairs) relocated from Rice Island to East Sand Island between 1999 and 2001, following habitat alteration on Rice Island. Wheat Triticum aestivum was planted and silt fencing erected to encourage vegetation growth, whilst suitable habitat was prepared on East Sand Island (see ‘Habitat creation – intertidal habitats’) along with several other interventions (see ‘Use decoys to attract birds to new nesting areas’, ‘Use vocalisations to attract birds to new nesting areas’ and ‘Control avian predators on islands’). The impact on conflict reduction (the purpose of the translocation) is discussed in ‘Move fish-eating birds to reduce conflict with fishermen’.
Move fish-eating birds to reduce conflict with fishermen

A before-and-after study in 1999-2001 on two small islands in the Columbia River Estuary, Oregon, USA (Roby et al. 2002), found that various interventions led to the relocation of a Caspian tern Sterna caspia colony (8,900 pairs in total) away from an important fishery. Tern chicks had a significantly lower proportion of juvenile commercial fish (such as coho salmon Oncorhynchus kisutch, steelhead O. mykiss and chinook salmon O. tshawytscha) in their diet following the movement of the colony to East Sand Island, compared with its original position on Rice Island (commercial fish making up 42% of the diet on East Sand Island vs. 83% on Rice Island, approximately 120 bill-loads sampled at each site each year). The predation of commercial fish by terns was a significant source of conflict with local fishermen, and translocation may well have reduced this conflict. Tern productivity was significantly higher at East Island than Rice Island in every year of the study. Individual interventions are discussed in ‘Use decoys to attract birds to new nesting areas’, ‘Use vocalisations to attract birds to new nesting areas’, ‘Control avian predators on islands’, ‘Habitat restoration/creation – intertidal habitats’ and ‘Translocations - Alter habitat to encourage birds to leave an area’.
Remove vegetation to create nesting areas

A before-and-after study on two small islands in the Columbia River Estuary, Oregon, USA (Roby et al. 2002), found that an entire Caspian tern Sterna caspia colony (approximately 8,900 pairs) relocated from Rice Island to East Sand Island between 1999 and 2001, following the creation and maintenance of 1.5-3.0 ha suitable nesting habitat on East Sand Island in 1999-2001. A bulldozer was used to clear debris and vegetation, tractors smoothed the bare sand and plants were removed physically and through spraying with herbicide each year. In addition, various other interventions were used to encourage birds to move to East Sand Island (see ‘Use decoys to attract birds to new nesting areas’, ‘Use vocalisations to attract birds to new nesting areas’ and ‘Control avian predators on islands’) and habitat on Rice Island was modified to encourage birds to leave (see ‘Alter habitat to encourage birds to leave’). The impact on conflict reduction (the purpose of the translocation) is discussed in ‘Move fish-eating birds to reduce conflict with fishermen’.
Control avian predators on islands

A before-and-after study on two small islands in the Columbia River Estuary, Oregon, USA (Roby et al. 2002), found that an entire Caspian tern Sterna caspia colony (approximately 8,900 pairs) relocated from Rice Island to East Sand Island between 1999 and 2001. Several interventions were used to encourage movement including the culling of a ‘limited number’ of glaucous-winged-western gull hybrids (Larus glaucensis x L. occidentalis). Reproductive success was also higher on East Island. This study is discussed in detail in ‘Move fish-eating birds to reduce conflict with fishermen’.
Use vocalisations to attract birds to safe areas

A before-and-after study on two small islands in the Columbia River Estuary, Oregon, USA (Roby et al. 2002), found that an entire Caspian tern Sterna caspia colony (approximately 8,900 pairs) relocated from Rice Island to East Sand Island between 1999 and 2001. Movement was encouraged by using between two and for audio systems, broadcasting the sounds of a Caspian tern colony, as well as several other interventions. This study is discussed in detail in ‘Move fish-eating birds to reduce conflict with fishermen’.
Use decoys to attract birds to safe areas

A before-and-after study on two small islands in the Columbia River Estuary, Oregon, USA (Roby et al. 2002), found that an entire Caspian tern Sterna caspia colony (approximately 8,900 pairs) relocated from Rice Island to East Sand Island between 1999 and 2001. Movement was encouraged by placing 253-415 decoys each year, as well as several other interventions. This study is discussed in detail in ‘Move fish-eating birds to reduce conflict with fishermen’.