Age class dynamics of Canada geese in the Central Flyway

ABSTRACT Abundance of temperate‐nesting Canada geese ( Branta canadensis ) in Central Flyway east‐tier states (ND, SD, NE, KS, OK, USA) increased since the 1970s. Hunting regulations were liberalized since the mid‐1990s in these states to increase harvest and reduce abundance of local populations. Because 2 age classes, juvenile and adult, are typically classified when banding, most dead‐recovery band analyses of Canada geese have only considered 2 age classes to estimate survival and recovery probabilities, despite a delayed breeding life history. We evaluated recovery distributions and survival and recovery probabilities of Canada goose age classes (i.e., juvenile [first year], subadult [second and third year], and adult [≥fourth year]) among Central Flyway east‐tier states relative to liberalized hunting regulations during 1990–2015. We also conducted simulations and evaluated bias in parameter estimates from 2‐age‐class dead‐recovery models when a subadult age class was not modeled. Models including 3 age classes were more supported than models including only 2 age classes. Mean juvenile survival estimates among states from the top 2‐age‐class models were 9–50% greater than an equivalent 3‐age‐class model, whereas differences were less or negligible for adult survival (−4% to −1%), adult recovery (1–12%), and juvenile recovery (−3–6%). Geese were primarily recovered in the state they were banded (range among states = 59–86%), and 91% of all recoveries occurred in the Central Flyway east‐tier states. Recovery distributions of subadults were broader and more northward than adults and juveniles. Recovery estimates (Brownie parameterization) of subadults among states ( = 0.091 ± 0.039 [SE] to 0.116 ± 0.029) were also generally greater than adults (0.061 ± 0.030 to 0.104 ± 0.033) and juveniles (0.049 ± 0.026 to 0.132 ± 0.041). Survival estimates of adults (0.713 ± 0.103 to 0.748 ± 0.119) and subadults (0.621 ± 0.197 to 0.801 ± 0.154) exhibited some decrease through time concurrent with liberalized harvest regulations, but survival estimate of juveniles (0.492 ± 0.093 to 0.686 ± 0.164) increased or were stable. Of the 5 Central Flyway east‐tier states, management actions to reduce local Canada goose populations were the most intensive in North Dakota and South Dakota, and these states had the greatest decrease in adult and subadult survival estimates. Our results provide some limited evidence that harvest regulations targeted at locally breeding Canada geese can affect their survival, have greatest effects when first implemented, and affect subadults from a broader spatial scale than adults and juveniles. More information is needed on how localized harvest regulations affect temperate‐nesting Canada geese from other areas, particularly subadults and molt migrants, and, conversely, how such geese affect the ability to achieve management objectives at varying spatial scales. Lastly, to minimize bias when analyzing temperate‐nesting Canada goose data, or other species with similar marking constraints and age‐class structure, consideration should be given to evaluating ≥3 age classes and using recapture data and joint live‐dead models when possible. © 2019 The Wildlife Society.

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