Social Indices of Breeding Productivity in Parkland Mallards

Abstract

Social indices were developed to assess breeding productivity of waterfowl based on weekly roadside surveys of social groupings (i.e., pairs, lone M, flocked M). We calculated social indices for mallard (Anas platyrhynchos) populations breeding on 16 study sites in the Canadian parklands from 1993 to 1998 using 7 previously developed indices. We also calculated duckling:pair ratios from our roadside counts, and we obtained independent measures of nesting effort, nesting success, female success, and fledging rate for these same 16 sites from a concurrent telemetry study. Social indices were correlated (r2 = 0.28‐0.67) with telemetry‐based measures of breeding productivity in 5 of 7 cases, with the strongest relationships deriving from indices that emphasized renesting effort. The 2 ineffective social indices (r2 ≤ 0.13) both measured early onset of nesting activity. Duckling:pair ratios could be calculated more easily from the same survey data and also were correlated (r2 = 0.26‐0.48) with measures of breeding productivity. Because surveys measuring late‐nesting effort also can enumerate early hatched ducklings, we recommend that waterfowl researchers use duckling:pair ratios rather than social indices because ducking:pair ratios are more easily interpretable. Development of sightability‐adjustment factors for pair and duckling surveys could further enhance the utility of duckling:pair ratios as indices of breeding productivity in mallards.

Variation in mallard vital rates in Canadian Aspen Parklands: The Prairie Habitat Joint Venture assessment

“…We conducted ground‐based surveys (Dzubin , Hammond ) to estimate mallard breeding‐pair density during late April and early May on 6 randomly chosen, non‐overlapping 2.6‐km 2 (8,050 m × 320 m) strip transects within the study area. We attempted to schedule pair counts when roadside pair surveys (Arnold et al ) revealed approximately a 1:1 ratio of paired to unpaired males (Wishart ). We surveyed all wetlands within transect boundaries and recorded mallards by social status (Dzubin , Wishart ).…”

Using sightability‐adjusted brood‐pair ratios to estimate waterfowl productivity

“…We obtained similar correlations between BPRs and hen success when we used unadjusted estimates of brood abundance (A. Pagano, University of Minnesota, unpublished data; see also Arnold et al ), but we do not recommend such an approach for long‐term studies that encompass a wide variety of wetland habitats. Detection probabilities for broods varied among years, and more importantly, the covariates that best predicted detection probabilities also varied among years.…”

“…In our study, SA‐BPRs explained approximately one‐third of the observed variation in hen success. Similarly, Arnold et al () found that uncorrected duckling–pair ratios explained 26% of the variation in mallard hen success and 48% of the variation in mallard nesting success estimates from 16 study sites in the Canadian Parklands. Not all of this lack of fit was necessarily due to imprecision of BPRs, because estimates of hen success are also affected by measurement error, but in our study imprecision of SA‐BPR estimates was approximately 3‐fold larger than imprecision of estimated hen success (Fig.…”

“…A variety of prominent historical studies used BPRs to examine long‐term productivity of waterfowl (Evans and Black , Stoudt , Hammond and Johnson , Leitch and Kaminski ). Furthermore, Arnold et al () found that duckling–pair ratios for mallards ( Anas platyrhynchos ) were better correlated with estimates of nesting success, hen success, and fledging rate (i.e., the no. of fledglings produced per breeding pair) in the Canadian Parklands than were social indices of breeding productivity.…”

Methods for surveying and estimating breeding waterfowl populations in the Prairie Pothole Region of Iowa

“…Thus, an increase in detection probability of grouped males, as shown by our study, would be expected as a result of this behavior. Understanding how detection differs among different indicated breeding pair criteria has important implications for breeding waterfowl survey design as indicated breeding pair criteria are used not only to accurately estimate breeding pair abundances but also as an index to waterfowl breeding success (Brasher et al 2002, Arnold et al 2008. Brasher et al (2002) suggested that indicated breeding pair criteria could lead to overestimated breeding pair abundances and underestimated production indices due to incorrectly classifying unpaired males as paired, although our study suggests potential underestimation of breeding pair abundances and overestimation of production indices by not accounting for imperfect detection of the various criteria.…”