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 (À4% to À1%), adult recovery (1-12%), and juvenile recovery (À3-6%). Geese were primarily recovered in the state they were banded (range among states ¼ 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 ( x ¼ 0.091 AE 0.039 [SE] to 0.116 AE 0.029) were also generally greater than adults (0.061 AE 0.030 to 0.104 AE 0.033) and juveniles (0.049 AE 0.026 to 0.132 AE 0.041). Survival estimates of adults (0.713 AE 0.103 to 0.748 AE 0.119) and subadults (0.621 AE 0.197 to 0.801 AE 0.154) exhibited some decrease through time concurrent with liberalized harvest regulations, but survival estimate of juveniles (0.492 AE 0.093 to 0.686 AE 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 ...

Assessing bias in demographic estimates from joint live and dead encounter models

“…White, Cordes & Arnold (2013) found that substantial variation in reporting rate did not appreciably increase bias in survival probabilities. Dooley et al (2019) reported greater bias than we found in survival and recovery probabilities when two age classes were modeled for Canada geese (Branta canadensis) in the North American mid-continent, and negligible bias, similar to our findings, when three age classes were modeled. Thus, while heterogeneity in survival can be ecologically important to estimate, we do not anticipate that unmodeled heterogeneity substantially and directionally biased estimates in our application of JE models as they were based only on adult females.…”

“…We recommend that researchers with reported mortality probability <0.19 and low recapture probabilities continue to interpret results cautiously. While we are not aware of research explicitly evaluating bias and RMSE in JE models, our results are similar to those from recent simulation studies that explored heterogeneity using waterfowl life histories and comparable model specification with DR models (White, Cordes & Arnold, 2013;Dooley et al, 2019). White, Cordes & Arnold (2013) found that substantial variation in reporting rate did not appreciably increase bias in survival probabilities.…”

Canada Goose Survival and Recovery Rates in Urban and Rural Areas of Iowa, USA

“…Most Canada goose band recovery analyses consider only 2 age classes because it is often only possible to age geese accurately as AHY or local in the field. We considered 3 age classes because geese undergo 3 behaviorally distinct life phases, and 2‐age‐class models can result in biologically improbable estimates (Heller 2010, Dooley et al 2019). Juvenile Canada geese typically have higher recovery rates (Heller 2010) and thus are expected to have lower survival than adults.…”

Exploratory Surveys of Migratory Birds Breeding in the Western and Central Canadian Arctic 2005–2011

“…We refer to these birds as cackling geese in the text, tables, and figures, following the American Ornithologist Union's species guidelines (Banks et al 2004). Birds that observers recorded as large Canada geese were likely molt-migrant Canada geese (Abraham et al 1999;Dooley et al 2019); we retained these in the observation-level database, but did not include them in any density maps or population estimates.…”