Exploring the consequences of reducing survey effort for detecting individual and temporal variability in survival

1. Long-term monitoring programmes often involve substantial input of skilled staff time. In

mark–recapture studies, considerable effort is usually devoted to both marking and recaptur-

ing/resighting individuals. Given increasing budgetary constraints, it is essential to streamline

field protocols to minimize data redundancy while still achieving targets such as detecting

trends or ecological effects.

2. We evaluated different levels of field effort investment in marking and resighting individu-

als by resampling existing mark–recapture–recovery data to construct plausible scenarios of

changes in field protocols. We demonstrate the method with 26 years data from a common

guillemot Uria aalge monitoring programme at a major North Sea colony. We also assess the

impact of stopping the ringing of chicks on our ability to study population demography using

integrated population models (IPM) fitted to data including information on breeding adults.

Different data sets were removed artificially to explore the ability to compensate for missing

data.

3. Current ringing effort at this colony appears adequate but resighting effort could be

halved while still maintaining the capacity to monitor first-year survival and detect the effect

of hatch date on survival prospects.

4. The IPM appears robust for estimating survival, productivity or abundance of the breed-

ing population, but has limited capacity to recover year-specific first-year survival when chick

data are omitted. If productivity were not monitored, the inclusion of chick data would be

essential to estimate it, albeit imprecisely.

5. Synthesis and applications. Post-study evaluation can help streamline existing long-term

environmental monitoring programmes. To our knowledge, this study is the first use of data

thinning of existing mark–recapture–recovery data to identify potential field effort reductions.

We also highlight how alternative monitoring scenarios can be evaluated with integrated pop-

ulation models when data are collected on different aspects of demography and abundance.

When effort reduction is necessary, both approaches provide decision-support tools for

adjusting field protocols to collect demographic data. The framework has broad applicability

to other taxa and demographic parameters, provided suitable long-term data are available,

and we discuss its use in different contexts.