Upper Rock Nature Reserve: A Management and Action Plan

15. The Yellow-legged Gull
15.1 History
15.2 Control
Gibraltar Ornithological and Natural History Society - GONHS
The Yellow-legged Gull
This chapter consists of a summary of the history and current situation regarding the status
of the yellow-legged gull, Larus michahellis, in Gibraltar. A more complete appraisal of
the current status of this species in Gibraltar can be gathered from Cortes et al. (2004) and
the annual reports that the GONHS prepares for the Ministry for the Environment.
The yellow-legged gull Larus michahellis (formerly Larus cachinnans) is the most common,
and certainly most conspicuous bird that nests in Gibraltar, but this has not always been
the case. Although it was recorded in the 19 th and early 20 th Century by several writers,
amongst them Saunders (1871), Irby (1895) and Verner (1909), it was not until 1934 that
Rait-Kerr mentions definite breeding (Cortes et al. 2004). Since then, the population of this
species has slowly increased, mainly breeding on inaccessible sea cliffs around the ridge of
the Upper Rock and the south district.
In the 1970s the nesting population was estimated to be 600 breeding pairs (Cortes et al.
1980). Nesting extended to roofs in the town, and exposed areas within the Upper Rock
became the focus of the gulls as they extended their breeding grounds. One particular site,
Rock Gun and the adjacent cliffs on the North Face of the Rock, was the cause of grave concern
to the Royal Air Force. The first flight of the fledged chicks would take them down to the
runway where the risk of a collision with an aircraft was menacing. In fact due to several bird
strikes and the resultant damage to aircraft, the RAF decided to carry out a gull cull. This
cull, which commenced in the spring of 1979, focused not only on the eggs and chicks, but
also on adult birds using the stupefacient alpha chloralose, and took place during the birds’
breeding season. The main area covered was the northern end of the Rock, which posed
the greatest threat to the aircraft landing on or taking off from the runway. This obviously did
not curtail the increase in the population, as other areas were not covered, and the yellowlegged
gull continued its expansion throughout the rest of the Upper Rock and other areas
around Gibraltar.
In 1982, as a result of a substantial and visually obvious increase in the population, the
RAF extended its operation to include other areas of the Upper Rock and the south district.
This practice continued on a yearly basis during the breeding season, targeting eggs and
chicks almost exclusively (a method that is known to be largely ineffective) until the MOD
reduced their presence in Gibraltar. Finlayson (1992) estimates the population at 2500 pairs,
although Cortes et al. (2004), gives a much higher estimate based on a survey by Mr. Peter
Rock (pers. comm.), of 30,000 birds at the end of the nesting season. The Royal Gibraltar
Regiment then continued with the venture, but by 1999 a combination of ineffective methods
and reduced culling meant that the gull population had grown to enormous proportions.
GONHS had been monitoring the situation and was well aware of the detrimental effects
this increase could have on the stability of the natural environment within the Upper Rock
Nature Reserve, as has occurred elsewhere. It was also conscious of the problems the gulls
were causing to the residents of the town area, and presented some suggestions to the
authorities. These arguments were accepted and a contract was awarded to GONHS. The
Gull Control Unit was therefore created in July 1997. This unit was tasked to control and cull
the gull population throughout the whole year as opposed to culling only during the breeding
season as had taken place in the past.
All areas in Gibraltar were targeted, but obviously the upper reaches of the Nature
Reserve and the eastern slopes were the most densely populated. Several methods were
examined and used, and for the first three years poison, hand nets, nest raking in the breeding
season, and catapults were the main techniques employed. Results during this period
were insufficient to make any significant inroads into the large population. Finally in 2000 the
acquisition of air rifles greatly improved the situation. Nest raking and the destruction of eggs
continued during the breeding season, but by far the most successful method was the targeting
of adult birds. By killing the adult bird, the nesting success of the pair had been eliminated,
whereas birds that are relieved of their clutch of eggs very often lay a second brood.
The yearly results to date, shown in table 1, demonstrates the efficient and substantial elimination
of a large percentage of the population.
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