Identifying demographic and environmental drivers of recruitment and population growth in a cavity‐nesting sea duck population

Abstract

Traits with the greatest proportional effects on fitness are typically conserved, and traits with larger temporal variation frequently play a dominant role in population dynamics. We examined recruitment patterns and population growth in common goldeneyes Bucephala clangula (hereafter goldeneye), using Pradel mark–recapture models from a long‐term nest box study (1997–2010). Our objectives were to estimate recruitment (f ) and population growth (λ) relative to recruitment origin group (in‐situ or unknown), investigate environmental and density dependent effects on these parameters, and evaluate potential immigration patterns. We detected group‐specific differences for f (in‐situ: 0.47 ± 0.13 SE, unknown: 0.31 ± 0.04), and the proportion of boxes occupied by goldeneyes the year prior to recruitment had a significant negative effect on recruitment for the in‐situ group (β = –1.04; 85% CI –1.29, –0.78), and a positive effect for the unknown group (β = 0.45; 85% CI 0.30, 0.61). The negative box occupancy effect in the year prior to recruitment, when in‐situ yearling goldeneyes prospect for potential nest sites, suggests that local nesting densities may limit recruitment of locally hatched females. We identified two competitive models for λ, which averaged 1.04 ± 0.03 and included interactions between recruitment origin group and a linear temporal trend, and the proportion of ducklings marked two years prior. By evaluating all levels of marking effort on λ, we determined that even if all hatched ducklings were marked in a given year, the resulting in‐situ λ was consistently lower than all observed population‐level λs during the study, indicating that individuals produced outside of study area nest boxes contributed to λ. Though female goldeneyes are considered highly philopatric, our results suggest that female natal and breeding dispersal may be more prevalent than previously thought, and the spatial scale at which these processes occur requires further investigation.

Episodes of high recruitment buffer against climate‐driven mass mortality events in a North Pacific seabird population

“…In some years only 20%-40% of double brooding attempts were successful (Johns et al, 2017), likely due The number of occupied boxes was retained in all the top models, and established breeders almost certainly outcompete potential new recruits for available nesting habitat. Similar findings have been reported for other bird colonies, where nesting density and high competition for available sites controls annual recruitment (Crespin et al, 2006;Lawson et al, 2017). Aside from simply occupying a site, territorial behaviour of Cassin's auklets in the form of acoustic displays and rushes up to 1 m from burrow entrances provides a mechanism for further limiting burrow density on the Farallones (Manuwal, 1974a) No single environmental covariate (of those tested) explained the variability in survival or occupancy better than a year-dependent term, given AIC selection results and assessment of inter-annual variation explained by covariates tested (see Supporting Information Table S2).…”

Relative Importance of Vital Rates to Population Dynamics of Wood Ducks

“…Positive relationships between annual survival, nest success, and future reproductive success supported the idea that quality of female wood ducks was heterogeneous (Kennamer et al 2016). Positive covariation between survival and reproduction in female common goldeneyes (Lawson et al 2017) and mallards (Arnold et al 2012) also supported the hypothesis that breeding females of these species differed in quality.…”

“…We showed SY female recruits that were not produced in nest boxes (i.e., putative immigrants) were important to the dynamics of the nest box population. Lawson et al (2017) also reported the important contributions that recruitment of immigrant females made to λ of common goldeneyes (Bucephala clangula) using nest boxes in Alaska, USA.…”