There is considerable ringing information which can be used to estimate the annual survival rates of adults and also young Herring Gulls but you have not used it. When I last did this, based on UK recoveries, there was a lower survival rate in the 1990-2000 and an suggestion that the survival rate had increased since. However, almost all ringing data in the UK is from coastal ringed young reared on natural and rural sites, e.g. islands. The situation with both numbers and survival rates for those nesting in urban areas does not exist in an adequate form.
As far as the UK is concerned, there is no evidence that the decline has continued in recent years. Also no comment is made of the numbers of immature individuals and the proportion of these surviving to maturity. This fundamental information is missing and so does not exclude that the decline in the late 1990s has reached a new population level.
I detect a lack of rigor in interpreting and evaluating published data and all seems to be accepted at face value. One has just to realise the poor level of accuracy which has been shown to exist in urban estimates to beg for greater caution. The gull is still very numerous (in millions)and as such, its risk of extinction is very low. ‘Near threatened’ is a rash category to apply at the present time.
An analysis of colour-ringing data from two large coastal colonies in Germany (Amrum – Norths Sea, Schleswig – Baltic Sea) showed that the annual survival rate of adults (including birds from the second year of life onwards) was constant over the study period (2005-2014) and on a high level (comparable to earlier decades, although those data are from studies elsewhere). In contrats, the annual survival rate during the first year of life (after fledging) decreased signifcantly from 0.77 to 0.45 (at least part of this decline may be attributed to the closure of landfills, wghich supported especially first-year birds during the winter). It appears that current decreases at the German coasts could be linekd to the low survival of offspring, leading to low recruitment into the population (Dierschke et al. 2021, Corax 24: 321-340). Actually, recruitment has decreased at to another North Sea colony from 1998-2000 to 2010-2014 (proportion of colour-ringed chicks entering the breeding stock at Helgoland – Dierschke et al. 2020, Ornithol. Jber. Helgoland 30: 1-97). At the same time, several Wadden Sea colonies showed breeding success good enough to maintain the population size, so the dramatic decline at the fromerly very large colony of Mellum is also thought to be related to low recruitment (Scheiffarth et al. 2020, Falke 67(6): 20-24.
However, for me it appears to be difficult to judge whether the recruitment problem justifies to upgrade from LC to NT or not. If really the closure of landfills is a reason, then it would be a decrease of a human activity harmful for the environment, and the same is true if also the reduction of discrded bycatch from fisheries is partly responsible for low juvenile survival rates. Therefore, at this time the decrease of the population size may just be the return to a relatively “natural” level.
My feeling is that the reasons for the decline need to be investigated more intensively, allowing to get an overview across the entire range of the species (and especially for those countries where strong declines are observed.
Save my name, email, and website in this browser for the next time I comment.
All comments must follow the rules of usage.
This site uses Akismet to reduce spam. Learn how your comment data is processed.
Sign up here to receive email alerts regarding BirdLife's Globally Threatened Bird Forums
Thank you for signing up!
Contact the BirdLife Red List Team under redlistteam [at] birdlife [dot] org.