Who escapes detection? Quantifying the causes and consequences of sampling biases in a long‐term field study

Abstract

Inferences drawn from long-term field studies are vulnerable to biases in observability of different classes of individuals, which may lead to biases in the estimates of selection, or fitness. Population surveys that monitor breeding individuals can introduce such biases by not identifying individuals that fail early in their reproductive attempts. Here, we quantify how the standard protocol for detecting breeding females introduces bias in a long-term population study of the great tit, Parus major. We do so by identifying females whose breeding attempts fail before they would normally be censused and explore whether this early failure can be predicted by a number of intrinsic and extrinsic factors. We investigate the effect of these biases on estimates of reproductive performance and selection. We show that females that go undetected by standard censusing because they fail early in their breeding attempt were less likely to have been previously trapped within our study site and were more likely to breed in poor-quality habitats. Furthermore, we demonstrate that this bias sampling had lead previous studies on this population to overestimate the reproductive performance of unringed females, which are likely to be immigrants to the population. Finally, we show that these biases in detectability influence estimates of selection on a key life-history trait. While these conclusions are specific to this study, we suggest that such effects are likely to be widespread and that more attention should be given to whether or not methods for surveying natural populations introduce systematic bias that will influence conclusions about ecological and evolutionary processes.

Selection on parental performance opposes selection for larger body mass in a wild population of blue tits

“…The model results remained qualitatively and quantitatively similar (see Supporting Information), but catching males on territories prior to breeding, or identification using unique color rings or PIT tags (as in Kidd et al. ), would aid in assigning these uncaught social males to validate this relationship. Similarly, individuals failing in a breeding attempt prior to hatching remain unknown.…”

“…For nests with known social fathers (because they were caught), the correct male would have been assigned in 92% cases if maximum paternity had been used, but this increases to 98 and 100% when restricted to nests where a male secured ≥50 and ≥75% paternity, respectively. The model results remained qualitatively and quantitatively similar (see Supporting Information), but catching males on territories prior to breeding, or identification using unique color rings or PIT tags (as in Kidd et al 2015), would aid in assigning these uncaught social males to validate this relationship. Similarly, individuals failing in a breeding attempt prior to hatching remain unknown.…”

“…If individuals are not missing at random, estimates of selection may be biased (Hadfield ), and Kidd et al. () found female great tits ( Parus major ) were less likely to be caught (due to early nest failure) if they were immigrants to the population, and when in poor quality habitats.…”

Environmental and genetic determinants of innovativeness in a natural population of birds

“…All nest-box nestlings are ringed and thus non-ringed juveniles caught in the non-breeding season are assumed to be immigrants. This is considered a reasonable assumption, given that the proportion of nestlings born in natural cavities in Wytham is estimated to be very low [89,90]. Age, sex [91] and natal origin (immigrant or Wytham-born) can thus be easily determined whenever individuals are trapped.…”

An occupancy approach to monitoring regent honeyeaters

“…Timing surveys to coincide with the early stages of breeding is also critical because the cumulative probability of nesting failure increases with time (Dinsmore et al ). Failing to locate regent honeyeaters during the early stages of their breeding period may therefore result in underestimated occupancy rates and overestimates of nesting success (Kidd et al ).…”