Southern black-backed gull control at the Waimakariri River

Southern black-backed gull (SBBG) control is part of a regular, successful programme that has been ongoing for many years with the aim of improving the biodiversity values of our region’s precious braided rivers. 

SBBG are large, predatory birds that have a significant negative impact on the braided river environment through predation, harassment and displacement of other threatened bird species, negative impacts on water quality, and risk of bird strike to overhead air traffic.

Below are the key points about why and how this work is done:

  • SBBG are predatory birds and are frequently observed harassing and directly predating other threatened native bird species, including the much smaller and critically threatened black-billed gull/tarāpuka. 
  • SBBG in the Waimakariri River also pose a risk of bird strike to air traffic passing overhead. 
  • For the last eight years, Environment Canterbury has undertaken work to try and control SBBG numbers in the Waimakariri River, for biodiversity and aviation safety reasons.
  • The most effective and humane way to reduce SBBG numbers in most circumstances is through alpha-chloralose control. There are some exceptions where alpha-chloralose is not accepted as the most effective method (i.e. outside of breeding season or if harm to non-target species is likely). In these cases other methods such as shotgun control can be considered, in consultation with an ornithologist.
  • Environment Canterbury follows a Best Practice Technical Standard for completing alpha-chloralose control in the Waimakariri River, which helps ensure the control is contained within a very small area and that risk of by-kill to other species is absolutely minimised. 
  • The toxin alpha-chloralose, an anaesthetic compound registered for black-backed gull control, is mixed with margarine on bread bait. The control operations are very contained with bait hand-laid and directly targeted at a group of birds.
  • The site is checked and cleared within 24 hours, including removing all uneaten baits and gull carcasses. 
  • Warning signs are placed at entry points to the operational areas and not removed until birds have been removed from the site.
  • The notification process for these control operations includes getting prior approval from adjacent landowners, alerting local vets if necessary/appropriate, and having the warning signage in place for the duration of the operation.
  • Although alpha-chloralose bread baits and carcasses can be toxic to domestic animals or people, this is a very rare occurrence because of the targeted and contained nature of the programme. We strongly advise people to avoid the control areas while signs remain in place and to not take their pets into these areas.

Black Billed Gull

Critically threatened black-billed gull/tarāpuka