Predators of Dusky Canada Goose goslings and the effect of transmitters on gosling survival

ABSTRACT The population of Dusky Canada Geese (Branta canadensis occidentalis) has been in long‐term decline, likely due to reduced breeding productivity. To identify causes of mortality, we monitored goslings marked with radio transmitters on the western Copper River Delta, Alaska, from 1997 to 1999. Almost all gosling mortality (96%; 81 of 84) was due to predation, with mink (Mustela vison) and Bald Eagles (Haliaeetus leucocephalus) the most important predators. Bald Eagles are also major nest predators and, thus, appear to play a key role in limiting the breeding productivity of Dusky Canada Geese. Daily survival rate for goslings to 28 d of age was lower (0.011; 95% CI 0.002?0.024) for those with transmitters than for those without, but did not differ for older goslings (29?45 d). Although finer resolution in the timing of the transmitter effect within the first 28 d was not possible, we found that, by limiting our sample to goslings that survived until after 2?3 d posthatching, support for a transmitter effect was much reduced. Younger, smaller birds are inherently more vulnerable than older birds to transmitter effects. In addition, the process of radio‐marking may have delayed the departure of goslings from nests and increased their risk of mortality shortly after hatching. Although radio transmitters may often be the only practical means for determining causes of mortality for young waterfowl, we suggest caution in using transmitters because of their potential negative effects, particularly during the first few days after hatching.     

Long-Term Survival and Harvest of Resident Canada Geese in Virginia

Resident populations of Canada geese (Branta canadensis) are of particular management interest throughout the eastern United States given increased human-wildlife conflicts due to regional increases in the Atlantic Flyway Resident Population. Within Virginia, USA, growth rates of resident goose populations have been reduced through extended harvest seasons and increased bag limits. Our objective was to investigate spatiotemporal patterns in survival rates and harvest rates of resident geese in Virginia over the past 25 years. We estimated annual survival, recovery, and harvest rates using mark-recapture data from 1990–2015 for individuals that were banded as resident birds during summer throughout the state. We tested for differences in annual survival probability and harvest rates of resident geese banded and recovered in 3 distinct goose hunt zones: the Atlantic, Southern James Bay, and Western hunt zones, each of which had different hunting regulations. We also tested for differences in survival and harvest rates between individuals banded in rural or urban sampling locations, and between age classes (i.e., after hatch-year or hatch-year). In general, survival rates of resident geese over the past 25 years in Virginia are declining. Differences in survival among the 3 goose hunt zones also suggests that current harvest management strategies have reduced survival rates of resident geese. Upon closer examination, we found differences in survival among zones, with resident geese in the Atlantic and Southern James Bay hunt zones showing more negative declines compared to resident geese in the Western zone. Resident geese banded in rural areas had higher survival than urban-banded geese. We also investigated the effects of sampling effort on survival estimates and found no difference in survival estimates among groups when using 75%, 50%, 25%, or 5% of the data randomly sampled from the full data set, suggesting that banding efforts of resident geese could be reduced and continue to inform adaptive management strategies for these populations throughout Virginia. © 2020 The Wildlife Society.     

Demographic Parameters of Rural and Urban Adult Resident Canada Geese in Georgia

ABSTRACT In many urban metropolitan areas, resident Canada goose (Branta canadensis) populations have grown to nuisance levels in spite of increasing harvest opportunity. To document differences in demographic parameters between urban and rural geese, I estimated probabilities of survival, recapture, recovery, and fidelity for adult resident Canada geese between 2001 and 2006 using banding, live recapture, and dead recovery data from 2 distinct banding locations in Georgia, USA. Adult survival rates were higher for urban geese (0.958, SE = 0.020) than for rural geese (0.682, SE = 0.049). Using estimated recovery probabilities of 0.505 (SE = 0.107) for urban and 0.463 (SE = 0.045) for rural geese, along with current estimates of crippling loss and reporting rate, the estimated mean harvest rate for urban geese was 0.029 (SE = 0.006) and for rural geese was 0.202 (SE = 0.020). Fidelity rates were similar between urban (0.730, SE = 0.033) and rural geese (0.713, SE = 0.069). This information suggests that urban segments of the Canada goose population have substantially higher survival than rural geese and are harvested at a very low rate, and that liberalizing hunting regulations may have little impact on Georgia's urban goose population. Wildlife managers may need to consider options other than sport hunting to control nuisance goose populations in urban areas.     

Ultrastructural and cytological changes in the muscle fibers of the pectoralis of the giant Canada goose (Branta canadensis maxima) in disuse atrophy during molt

Summary Adult male Branta canadensis maxima were collected from a nonmigratory feral population during their premolt, molt and postmolt phases. Lean dry weight of the pectoralis muscle decreased significantly (p0.0001) during molt, as a result of disuse atrophy. Histochemical analysis revealed that the region of the pectoralis muscle sampled consisted of Red (fast-twitch oxidative-glycolytic) and White (fast-twitch glycolytic) muscle fiber types, in an approximate ratio of 9 to 1. There was no significant (p= 0.1238) difference in the relative percentages of the two fiber types during the three periods of study. There was, however, a significant decrease in mean cross-sectional area of both Red (p0.0194) and White (p0.0001) fibers during molt. Red and White fiber areas were strongly correlated with each other during molt (r ²=0.76, p=0.0010) and postmolt (r ²=0.70, p=0.0052), but not during premolt (r ²=0.02, p=0.7626). The latter finding may be related to fiber-type specific hypertrophy in premolt breeding males. Analysis of ultrastructure revealed that there was a significant (p=0.0003) decrease in the mean myofibrillar crosssectional area, and a significant increase in both the density (p=0.0227) and total number (p=0.0058) of myofibrils within the muscle fibers of the molting birds. These results indicate that the myofibrils split longitudinally during moltassociated disuse atrophy. A significant (p=0.0375) reduction in the amount of non-myofibrillar material (mitochondria) was also observed in the periphery of the muscle fibers of the molting birds. The changes observed during disuse atrophy are neither as pathological nor as extreme as those induced by experimental models of avian muscle atrophy.     

Estuarine survival and migratory behaviour of Atlantic salmon Salmo salar smolts

To estimate mortality rates, assess the spatio‐temporal dynamics of natural mortality and examine migratory behaviour during the fresh to saltwater transition, 185 wild Atlantic salmon Salmo salar smolts were implanted with coded acoustic transmitters. Seaward migration of tagged S. salar from four river systems in an area of Nova Scotia, Canada known as the Southern Upland was monitored using fixed receivers and active telemetry over 3 years. Cumulative survival through the river, inner estuary, outer estuary and bay habitats averaged 59·6% (range = 39·4–73·5%). When standardized to distance travelled, survival rates followed two patterns: (1) constant rates of survival independent of habitat or (2) low survival most frequently associated with inner estuary habitats. In rivers where survival was independent of habitat, residency periods were also independent of habitat, post‐smolts exhibited few upstream movements, took a more direct route to the ocean and reached the ocean rapidly. Alternatively, in rivers where survival was habitat specific, residency was also habitat specific with overall increased residency, more frequent upstream movements and delayed arrival to the open ocean. The sudden disappearance of most (75–100%) smolts and post‐smolts assumed dead during the course of this study warrants further examination into the role of avian predators as a mortality vector.     

Winter Survival of Female Ring-Necked Ducks in the Southern Atlantic Flyway

North American waterfowl harvest regulations are largely guided by the status of breeding populations. Nonetheless, understanding the demographics of wintering waterfowl populations can elucidate the effects of hunting pressure on population dynamics. The ring-necked duck (Aythya collaris) breeds and winters in all North American administrative flyways and is one of the most abundant and most harvested diving ducks in the Atlantic Flyway. But few studies have investigated the winter ecology of ring-necked ducks. We used a known-fate analysis to estimate period survival probability using data from 87 female ring-necked ducks marked with satellite transmitters in 2 regions of the southern Atlantic Flyway during winters of 2017–2018 and 2018–2019. Winter (128-day) survival probability was higher for individuals in the Red Hills region of southern Georgia and northern Florida (0.875, 95% CI = 0.691–0.952) than individuals in central South Carolina (0.288, 95% CI = 0.082–0.514). We attribute the regional disparity in winter survival probabilities to differences in hunting pressure, which are reflected in the number of harvests we observed in each region. Our findings warrant further investigation into regional variation in winter survival of southern Atlantic Flyway ring-necked ducks, and, specifically, the relationship between variable harvest pressure and winter survival and its influence on ring-necked duck population dynamics and adaptive harvest management decisions. © 2020 The Wildlife Society.     

Comparison of the egg flotation and egg candling techniques for estimating incubation day of Canada Goose nests

ABSTRACT Both egg flotation and egg candling have been used to estimate incubation day (often termed nest age) in nesting birds, but little is known about the relative accuracy of these two techniques. We used both egg flotation and egg candling to estimate incubation day for Canada Geese (Branta canadensis interior) nesting near Cape Churchill, Manitoba, from 2000 to 2007. We modeled variation in the difference between estimates of incubation day using each technique as a function of true incubation day, as well as, variation in error rates with each technique as a function of the true incubation day. We also evaluated the effect of error in the estimated incubation day on estimates of daily survival rate (DSR) and nest success using simulations. The mean difference between concurrent estimates of incubation day based on egg flotation minus egg candling at the same nest was 0.85 ± 0.06 (SE) days. The positive difference in favor of egg flotation and the magnitude of the difference in estimates of incubation day did not vary as a function of true incubation day. Overall, both egg flotation and egg candling overestimated incubation day early in incubation and underestimated incubation day later in incubation. The average difference between true hatch date and estimated hatch date did not differ from zero ( days) for egg flotation, but egg candling overestimated true hatch date by about 1 d (true – estimated; days). Our simulations suggested that error associated with estimating the incubation day of nests and subsequently exposure days using either egg candling or egg flotation would have minimal effects on estimates of DSR and nest success. Although egg flotation was slightly less biased, both methods provided comparable and accurate estimates of incubation day and subsequent estimates of hatch date and nest success throughout the entire incubation period.     

Factors affecting the responses of female Canada Geese to disturbance during incubation

During incubation, Canada Geese (Branta canadensis) and other waterfowl flush from their nests in response to the approach of potential predators and subsequently return to nests after the threat of predation has abated. Differences among individuals in their responses to such disturbance (e.g., how close a potential predator approaches before flushing) are thought to reflect variation in female age, the reproductive value of clutches, and nest site characteristics. From 26 April to 26 May 2010, we examined the possible effects of these factors on the behavior of female Canada Geese (B. c. interior) on Akimiski Island, Nunavut. We used humans as surrogate predators and flushing distance and return time after disturbance as response variables. The distance at which females flushed in response to approaching humans was best explained by the density of vegetation around nests, with females on better concealed nests flushing at closer distances. We also found a weak relationship between return time and clutch size, with females with larger clutches returning to nests sooner. The frequency of human visits did not affect either female flushing distance or return time. Female Canada Geese in our study appeared to minimize risk of their own injury or death (future reproductive potential) in escape decisions, whereas return times appeared to minimize the risk of nest predation (current reproductive investment).     

Using a Cost-Effectiveness Model to Determine the Applicability of OvoControl G to Manage Nuisance Canada Geese

Abstract: OvoControl G is a relatively new product that reduces hatchability of Canada goose (Branta canadensis) eggs, and few data are available on its cost effectiveness. Variables such as presence of nontargets, alternative foods, and public support can affect cost efficacy. We present a model that uses these and other factors to estimate the cost of application of OvoControl G for managing nuisance Canada geese. We found that at low goose densities (<35 pairs of geese), fixed labor was a significant portion of costs. As goose densities increase, OvoControl G becomes more cost effective than other methods, such as egg oiling or addling. Managers can use this model to determine whether OvoControl G will provide a successful and cost-effective treatment for population control of Canada geese in specific management areas.     

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

Once extirpated from much of their North American range, temperate-breeding Canada geese (Branta canadensis maxima) have reached high abundance. As a result, focus has shifted from restoration to managing harvest and addressing human-goose conflict. Conflict persists or is increasing in urban areas throughout the Mississippi Flyway. Managers need more information regarding demographic rates to determine how hunting affects geese breeding in urban areas and what management actions may be required to achieve management goals. We estimated survival, dead recovery, live recapture, and fidelity probabilities using data from 77,872 Canada geese banded in Iowa, USA, during 1999–2019 using Burnham joint live-dead band recovery models. Factors predicted to affect parameters in candidate models included age (juvenile, subadult, adult), banding site (urban, rural), time, trend, harvest regulation index, and winter severity index. We predicted Canada geese banded in urban areas would have higher survival and lower dead recovery rates than geese banded at rural sites. The top model indicated support for age and banding site effects, and trends in survival and recovery rate (Brownie parameterization). Adult survival was similar for urban (0.75; range = 0.60–0.92) and rural (0.75; range = 0.66–0.82) geese and relatively constant across years. Mean juvenile survival was lower in urban (0.74; range = 0.48–0.93) than rural (0.85; range = 0.68–0.92) areas. Survival increased for urban-banded juveniles and recovery rates increased during liberalization of harvest regulations and decreased after regulations stabilized. Recovery rates of subadults increased for the urban and rural groups. Our results suggest Canada geese breeding in urban areas contribute to harvest and specialized regulations can affect these populations. Harvest regulations in place during our analysis may not have reached a threshold required to observe substantial changes in survival. Current human-goose conflict in urban areas suggests survival has not decreased to a level required to completely address conflict via reduction in goose abundance. Managers may consider additional liberalization of harvest regulations and monitoring via banding to determine to what degree hunter harvest contributes to reducing human-goose conflict and what additional management actions will be required to achieve goals. © 2020 The Wildlife Society.     

Introduced Swedish Canada geese (Branta canadensis) have low levels of genetic variation as revealed by DNA fingerprinting

The Swedish, Finnish and Norwegian population of Canada geese (Branta canadensis), now amounting to some 30–50 000 birds, was founded by only five individuals. We used DNA fingerprinting to assess the level of genetic variability in minisatellite loci of Swedish Canada geese from two northern areas. For comparison, we estimated the minisatellite variability in lesser white-fronted geese (Anser erythropus), barnacle geese (Branta leucopsis) and a reintroduced stock of Canadian giant Canada geese (Branta canadensis maxima). The mean similarity between Swedish Canada geese was 0.76 ± 0.15, which is higher than recorded for any other natural bird population. The high similarity implies that a fourfold increase of homozygosity has taken place in this population. The probable cause for the loss of variation is the low number of birds originally introduced and a history of repeated translocations, leading to a sequence of founder events. As a consequence of the high similarity, it has not been possible to use DNA fingerprinting for determination of parenthood in the population studied.     

Increased rice flooding during winter explains the recent increase in the Pacific Flyway White‐fronted Goose Anser albifrons frontalis population in North America

Despite declines in numerous migratory bird populations due to global climate and landscape changes, the Pacific Flyway population of Greater White‐fronted Geese Anser albifrons frontalis in North America has flourished over recent decades. However, the demographic foundations of the population increase remain unclear, largely due to sparse data. In this study, we used a Bayesian integrated population model (IPM) to maximize information from multiple data sources including coordinated population survey, ring‐recovery and hunter‐harvested goose tail data. We estimated demographic parameters and assessed the role of several possible drivers of the observed population increase, including density‐dependent processes, agricultural land use change and climate conditions in both the wintering and the breeding season, while also accounting for the impacts of harvest. Non‐harvest survival of all geese was 0.83 (95% credible interval (CRI): 0.70–0.96) before legislation restricted post‐harvest rice field burning, and 0.98 (95% CRI: 0.94–1.0) afterwards. We detected a negative effect of density‐dependent processes and a positive effect of El Niño‐Southern Oscillation on non‐harvest survival with high certainty. Kill rates were 0.11 (95% CRI: 0.09–0.12) for adults (after hatch year) and 0.26 (95% CRI 0.21–0.31) for juveniles (hatch year), resulting in annual survival rates of 0.81 (95% CRI: 0.69–0.89) for adults and 0.67 (95% CRI: 0.56–0.76) for juveniles. The ratio of juvenile birds to adults in the population was on average 0.36 (95% CRI: 0.29–0.45) and was driven by negative density‐dependent processes with high certainty. Our results suggest that the ban on rice field burning and subsequent high frequency of flooding as an alternative rice decomposition practice was the primary driver of the Pacific white‐fronted Goose population increase. The effects of climate change and density dependence were not strong enough to suppress the benefit of flooded rice. Given sparse demographic data for Pacific white‐fronted Geese, we were only able to uncover drivers of demography using IPMs. We encourage practitioners with sparse data similarly to consider forming IPMs to determine the drivers and mechanisms for population change and to prioritize future data collection.