Yellow legged Gull Larus michahellis, is the most common breeding LWHG in Portuguese coast, with 15.993 pairs (Catry 2002; Morais et al. 2003) at Berlenga and 943 to 993 pairs along the rocky coast during 2007 Portuguese breeding bird atlas survey.
In 1994, 95 and 96, ICN, Portuguese Nature Conservation Institute, decided to eliminate a good part of their breeding population in Berlengas (44.000 individuals estimated) using an avian toxin DRC-1339 (developed to control corvids and gulls in US), aiming to restore the island biodiversity.
Toxic bait, like sardines and bread were used near nests in breeding season, to be assure that only adult breeding birds could eat it.
During the 3 year campaign Ylg population at Berlengas have been reduced to an estimated 24.000 individuals, being 16.000 gulls eliminated only in the first year.
During the gull eradication campaign, ICN started to ring nestlings with darvics to track their movements and habits, trying to know a little more about their ecology.
In 1995 they used yellow ring with letter B, and in the following years till 1998, the same yellow darvics but using 3 letters.
Ylg B Ringed as pullus in 1995, and raised by a lucky pair that didn’t eat the toxic bait, seen in August 2011 at Molhe Leste, Peniche.
Ylg CUZ Ringed as pullus in 1997, and seen in August 2011 at Molhe Leste, Peniche. This was the first control since the ringing date. On seven Portuguese color ring readings made that day only one had 1 sighthing, in 2004 made by a foreigner observer.