Estimating mortality rates among passerines caught for ringing with mist nets using data from previously ringed birds

Area of Science:

• Ornithology
• Wildlife Ecology
• Conservation Biology

Background:

• Mist netting is a widely used method for bird capture in scientific ringing.
• There is limited quantitative data on the risks of mortality and injury to birds during mist netting.
• Ethical concerns and potential data biases arise from capture-related mortality.

Purpose of the Study:

• To estimate the mortality rate of passerines captured using mist nets.
• To identify factors influencing bird mortality during mist netting.
• To provide recommendations for minimizing risks and improving data collection.

Main Methods:

• Analysis of 1.5 million bird records from the British and Irish Ringing Scheme.
• Application of generalized linear mixed-effects models to assess influencing factors.
• Examination of species, age, mass, season, time, capture history, and predator occurrence.

Main Results:

• The average mortality rate was estimated at 0.0011.
• Most mortality (approx. 70%) occurred before birds were removed from nets.
• Juvenile birds and specific species (Chiffchaff, Bullfinch) exhibited higher mortality risks; winter predation increased risk.

Conclusions:

• Mist netting is a generally safe bird capture technique when conducted by trained individuals.
• Recommendations include improved data collection on mortality/injuries, increased care for high-risk species/seasons, and robust net-checking procedures.
• Ringing Schemes should collate and share capture-related mortality data to enhance understanding and minimize risks.