Study

Behavioural responses of black-headed gulls and avocets to two methods of control of gull productivity

  • Published source details Hill D. & Player A. (1992) Behavioural responses of black-headed gulls and avocets to two methods of control of gull productivity. Bird Study, 39, 34-42.

Summary

As gulls Larus spp. are believed to reduce the breeding success of avocets Recurvirostra avosetta, through competition for nesting space and the predation of eggs and young, gull productivity is often controlled at avocet breeding sites in the UK. This study investigated the effects on black-headed gull Larus ridibundus behaviour of two commonly used methods of controlling gull productivity, at Havergate Island, Suffolk, eastern England.

Black-headed gull clutches at Havergate were destroyed either by raking nests and eggs (at Main and North lagoons) or by injecting eggs with formalin (at Doveys and Belpers lagoons). Early clutches on Main and North lagoons were collected and removed on 11 May 1988; subsequent clutches were raked on 22 May, and again on 1 or 3 June. Eggs at Doveys and Belpers lagoons were injected with formalin on 13-17 May, 25-27 May, and (at Doveys lagoon) 15-17 June.

Hour-long observations of black-headed gull and avocet behaviour were carried out: i) on the three days prior to each control; ii) during the first hour following the end of control, and; iii) every four days after the control programme had ended (“longer term”).

Aside from a slightly lower proportion of black-headed gulls on nests at Main lagoon, there were no significant differences in gull behaviour between lagoons prior to control measures. However, during the first hour following the end of control measures, gulls were significantly more active at lagoons where nests were raked than at those where eggs were injected (where more than half of gulls returned to their nests). Differences between the two treatments were also apparent in the longer term, with significantly more disturbed behaviour (as well as higher rates of intra- and inter-specific aggression) observed for gulls at lagoons where nests were raked rather than injected.

There were no determinable effects of gull control treatment on avocet behaviour, though avocets returned to their nests after control measures more quickly at lagoons where gull nests had been raked. The study did not attempt to investigate the impact of the two treatments on avocet productivity.


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