Breeding Population Estimates Research Articles

Balancing Waterfowl Hunting Opportunity and Quality to Recruit, Retain, and Reactivate

ABSTRACTWaterfowl hunter numbers and waterfowl populations were closely correlated until the past 2 decades when hunter numbers declined despite near‐record breeding population estimates for ducks in North America. As a result, efforts to recruit, retain, and reactivate (R3) waterfowl hunters have been promoted by the North American Waterfowl Management Plan community because hunters are a key source of funding for wetland‐wildlife habitat conservation and management. Increasing access and opportunity for hunting appears to be the primary R3 strategy in North America. We suggest that hunt quality is an equal, if not more important, facet of waterfowl hunter R3 that is substantially overlooked and undervalued by current R3 initiatives. We contend that providing abundant access and opportunity to hunt waterfowl alone, especially if it jeopardizes hunting quality, is inadequate. We urge the R3 community to integrate principles and methods used within the human dimensions field to focus on the relationships between quality, motivation, and satisfaction across various audiences and market segments. Such an approach will help R3 initiatives establish an empirical evidence base to develop strategies specifically focused on identifying key hunt quality or opportunity factors. © 2020 The Wildlife Society.

A census of breeding Manx Shearwaters Puffinus puffinus on the Pembrokeshire Islands of Skomer, Skokholm and Midland in 2018

We present the results of a census of the Manx Shearwaters Puffinus puffinus nesting on the three Pembrokeshire islands of Skomer, Skokholm and Midland (formerly Middleholm), Pembrokeshire, undertaken in 2018. The breeding population estimates were largely in line with those made in 2011–2013, but differed markedly from 1998; this difference seems to be due to the different methods used in 1998 rather than any marked change in population size. Despite attempts to refine the estimation of response rate to call playback, the error of the population estimates remains large, illustrating the logistical and analytical challenges of making seabird censuses using call playback. Nonetheless, the population estimates are large and the spatial distribution of occupied burrows is consistent between censuses, and thus Wales may hold more than half of the world’s breeding population of Manx Shearwaters.

Breeding populations of Little Ringed Plover Charadrius dubius and Ringed Plover Charadrius hiaticula in the United Kingdom in 2007

ABSTRACTCapsule: The 2007 national survey of the UK breeding population of Little Ringed Plovers shows a further spread into Scotland and Wales since the previous survey in 1984. In contrast, there has been a significant decrease in the Ringed Plover breeding population.Aims: To provide new breeding population estimates in the UK and Great Britain for Little Ringed Plover Charadrius dubius and Ringed Plover Charadrius hiaticula in 2007 and investigate changes in breeding distribution and habitat use since 1984.Methods: Breeding population estimates were made by combining counts of pairs from ‘key sites’ (2 × 2 km tetrads known to be occupied in/since 1984) and estimates of the numbers of pairs away from these sites based on stratified sampling. Survey periods for Little Ringed Plover: 15 April to 15 July, three visits; Ringed Plover: 15 April to 30 June, two visits.Results: Population estimates, for 2007, of 1239 (95% confidence intervals: 1175–1311) pairs of Little Ringed Plover and 5291 (5106–5478) pairs of Ringed Plovers were calculated for Great Britain, with 5438 (5257–5622) pairs of Ringed Plover estimated in the UK. Counts of Ringed Plover at inland and coastal sites, covered in both 1984 and 2007, decreased by 83% and 53%, respectively. The Little Ringed Plover population has expanded in range northward and westward since 1984. Main habitats used in 2007 by Little Ringed Plover were inland gravel and sand (25.9%) and river shingle (17.8%); and, for Ringed Plover, coastal shingle and sand (38.5% and 13.7%, respectively) and machair plus associated habitats (23.8%) in the Outer Hebrides.Conclusions: Between 1984 and 2007, the Little Ringed Plover breeding population in the UK increased considerably, expanding northward and westward, with increased use of river shingle habitats. During the same period Ringed Plover breeding numbers in the UK declined considerably in both coast and inland habitats, likely to be due to human disturbance and habitat change, respectively.

Evaluating the waterfowl breeding population and habitat survey for scaup

ABSTRACTPotential bias in breeding population estimates of certain duck species from the Waterfowl Breeding Population and Habitat Survey (WBPHS) has been a concern for decades. The WBPHS does not differentiate between lesser (Aythya affinis) and greater (A. marila) scaup, but lesser scaup comprise 89% of the combined scaup population and their population estimates are suspected to be biased. We marked female lesser scaup (i.e., marked scaup) in the Mississippi and Atlantic Flyways, Canada and United States, with implantable satellite transmitters to track their spring migration through the traditional and eastern survey areas of the WBPHS, 2005–2010. Our goal was to use data independent of the WBPHS to evaluate whether breeding population estimates for scaup were biased and identify variables that might be used in the future to refine population estimates. We found that the WBPHS estimates of breeding scaup are biased because, across years, only 30% of our marked scaup had settled for the breeding period when the strata in which they settled were surveyed, 43% were available to be counted in multiple survey strata as their migration continued during the WBPHS, 32% settled outside the WBPHS area, the number of times a marked scaup was available to be counted by survey crews varied positively with the latitude that a marked scaup settled on breeding areas, the probability of a marked scaup being in a stratum while it was surveyed varied among years, and these probabilities were positively correlated with the traditional and eastern breeding population estimates for scaup. Annual population estimates derived from banding data provide a less biased and preferable method of monitoring scaup population status and trend. Development of models that include metrics such as survey stratum latitude and annual spring environmental conditions might potentially be used to improve scaup breeding population estimates derived from the WBPHS, but independent estimates from banding data would be important to evaluate such models. © 2018 The Wildlife Society.

An Updated Avifauna of Moku‘ae‘ae Rock Islet, Kaua‘i

Moku‘ae‘ae Rock Islet is located off the north shore of Kaua‘i and is protected as a Hawai‘i State Seabird Sanctuary. In the late 1970s it was also the site of a cross-fostering project for the endangered Newell’s Shearwater, Puffinus newelli . Few avifauna surveys have been undertaken on the islet, and none since 2007. In 2013 and 2015, we conducted burrow searches across the entire islet to obtain breeding population estimates for each species and to evaluate whether the Newell’s Shearwater had become established as a breeding species after the cross-fostering project. Auditory surveys were also conducted for 2 hr after sunset and 1.5 hr before sunrise, which are the peak calling periods for the Newell’s Shearwater on Kaua‘i. A total of seven seabird species was recorded on the islet, of which three, Bulwer’s Petrel, Bulweria bulwerii ; Wedge-tailed Shearwater, Ardenna pacifica ; and Red-tailed Tropicbird, Phaethon rubricauda , were confirmed breeding. This is the first time Bulwer’s Petrel has been confirmed breeding on Moku‘ae‘ae. Searches for Newell’s Shearwater did not produce evidence that this species breeds on the islet, suggesting that the cross-fostering project was not successful. Although the islet is small, it represents an important refuge for seabird species. However, high levels of depredation were recorded on Bulwer’s Petrel; we conclude that these were all killed by the introduced Barn Owl, Tyto alba , based on disposition of the bodies and the injuries they had sustained. Management recommendations for the islet include creation of a management plan, annual breeding bird surveys, annual rat monitoring, and Barn Owl control.

Survival and harvest characteristics of giant Canada geese in eastern South Dakota, 2000-2004

The population of giant Canada geese (Branta canadensis maxima) in eastern South Dakota has increased substantially since reintroduction efforts began in the 1960s. Breeding population estimates of Canada geese exceeded the population management objective of the South Dakota Game, Fish and Parks by the mid-1990s and has continued to increase at an estimated rate of 3 to 5% per year. Goose-related crop damage complaints have also increased. In 1996, a September hunting season (September 1 to 15) was implemented in 10 counties in eastern South Dakota and was expanded in 2000 to include most of eastern South Dakota. We initiated this study during 2000 to 2004 to estimate survival, harvest, and recovery rates of giant Canada geese. We captured and leg-banded Canada geese in 7 counties in eastern South Dakota during the summers of 2000 to 2003. Of the total leg-banded sample (n = 3,839), we recovered 648 bands during the same year that they were placed on geese (i.e., direct harvest rate), and we recovered 645 banded geese in later years (i.e., indirect recovery rate). Estimates of annual survival rate (95% CI) for adults and immatures were 0.52 (0.46 to 0.59) and 0.68 (0.57 to 0.79), respectively. Estimates of annual recovery rates (95% CI) for adult and immature geese were 0.16 (0.13 to 0.19) and 0.18 (0.14 to 0.21), respectively. Of the total recoveries, 77 and 69% of direct and indirect band recoveries, respectively, occurred in South Dakota. The composite harvest rate estimate during the period studied was 0.22 (0.20 to 0.24). Forty-nine percent of adult recoveries and 44% of immature recoveries (direct and indirect pooled for both age classes) occurred during the September season. In comparison to a previous band-recovery study of resident giant Canada geese in eastern South Dakota, survival rates for both adult and immature geese have declined, while recovery and harvest rates have increased. Survival estimates for this study were some of the lowest documented for giant Canada geese. However, it appears that even with a September hunting season targeting the local breeding population, declines in adult survival documented during this study are not reducing the population. Alternative management strategies may be necessary to reduce the population to achieve the management objective.

Assessing the accuracy of plotless density estimators using census counts to refine population estimates of the vultures of Kruger National Park

Breeding population estimates for three vulture species in Kruger National Park (KNP), South Africa, were made in 2013 using data from aerial censuses and a plotless density estimator (PDE). PDEs are distance-based methods used to assess sparse populations unsuitable for plot-based methods. A correction factor was applied to the 2013 estimates to reflect the difference between the survey counts and the PDE figures. We flew additional censuses across most of KNP and counted all visible nests to assess the 2013 estimates. Survey counts were within 95% confidence limits of corrected PDE estimates for White-backed Vulture Gyps africanus (count: 892; estimate: 904 [95% CI ±162]), at the limit of confidence for White-headed Vulture Trigonoceps occipitalis (count: 48; estimate: 60 [±13]) and outside confidence limits for Lappet-faced Vulture Torgos tracheliotos (count: 44; estimate: 78 [±18]). Uncorrected PDE estimates accurately reflected White-headed and Lappet-faced Vulture nest counts. The clustered patterns of White-backed Vulture nests and dispersed patterns of White-headed and Lappet-faced Vulture nests offer an explanation for these results and means that corrected PDE densities are inaccurate for estimating dispersed nests but accurate for estimating clustered nests. Using PDE methods, aerial surveys over ∼35% of KNP are probably sufficient to assess changes in these vulture populations over time. Our results highlight these globally important breeding populations.

Abundance, distribution and trend of the lesser spotted eagle (Aquila pomarina) breeding population in Slovakia

Abstract Several estimates of the lesser spotted eagle breeding population in Slovakia were published in 1955-2002. In this study we estimate the breeding population of the lesser spotted eagle by 1997 and 2014. By 1997, the estimated size of the breeding population was 762 pairs. In 2002 an estimate of the population size by 2000 was published at 800-900 pairs. By 2014 we estimate the breeding population of the lesser spotted eagle in Slovakia at 600-800 pairs and the declining population trend in 2000-2013 at -23%. Our estimate is supported by the extrapolation from data obtained in 2011-2013 in eight selected Special Protection Areas (SPAs) within a framework of the project LIFE09 NAT/SK/000396 “Conservation of Aquila pomarina in Slovakia”. When analyzing abundance, density and trends in the species’ entire breeding range in Slovakia we first summarised the numbers of breeding pairs, their densities and trends within the selected SPAs and then explored the differences among them using ANOVA and cluster analysis. For the eight SPAs as a whole (n = 8) or partitioned by a grid of the Databank of Slovak Fauna (n = 119 squares) we calculated the interval estimates of the mean number of pairs (unweighted and weighted arithmetic means and medians). By summarising these estimates and extrapolating to the species’ entire breeding range in Slovakia (c. 28,935 km2) while increasing the sample size (n = 8, 9, 11 and 1 2 SPAs), the size estimates stabilise at a level of 670 (mean with 95%LCL = 507 and 95%UCL = 834) or 765 (median with 95%LCL = 393 and 95%UCL = 841 ) breeding pairs. The most reliable estimate of the breeding population of the lesser spotted eagle in Slovakia by 2014 is a median of 765 pairs with a 95% confidence interval from 393 to 841 pairs and an interquartile range from 418 to 835 pairs. We estimate a 23% decrease in the breeding population during 2000-2013, i.e. a small decrease -1 (20-49%). Three methods of estimating were used: 1 ) comparing the numbers of pairs in the selected SPAs between 2000 and 2014 - indicates a decrease of -26%; 2) comparing the numbers of pairs from long-term monitoring in five areas (orographic units Vihorlatské vrchy Mts, Laborecká vrchovina Upland, Volovské vrchy Mts, Orava and Horné Ponitrie Regions) by the 1990s and 2014 - indicates a decrease of -20%; 3) comparing the numbers of pairs by 1997 in selected areas within the boundaries of the current SPAs with the number of pairs in the same SPAs by 2014 - indicates a decrease of -23%. In the eight selected SPAs the estimated decline was even more pronounced, reaching a median trend of -35% in the 95% confidence interval from -54% to +25%. The estimate by 1997 fits in with an increasing trend of published breeding population estimates in Slovakia during 1955-2002. The estimate by 2014 is lower than the estimate by 2000, and for the first time ever a declining trend is recorded. By 2014 the breeding grounds of the lesser spotted eagle in Slovakia embrace an area of c. 28,935 km2. Taking an estimate of 600-800 breeding pairs, the mean density varies between 2.1-2.8 pairs.100 km-2.

Effects of re‐breeding rates on population size estimation of biennial breeders: results from a model based on albatrosses

Estimating total breeding populations (I) for species that exhibit biennial breeding is generally done from counts of individuals that breed in each year (N), but can be complicated by the fact that the proportion of individuals breeding varies from year to year. Partly, this reflects the proportion of individuals that re‐breed in successive years (re‐breeding rate, p), which is largely, although not exclusively, governed by reproductive failure. Here we show that variation in counts of breeding individuals not only reflects changes in total breeding population but can be sensitive to and powerfully driven by variation in p. A simulation of annual field counts of a bird exhibiting biennial breeding was constructed to explore the effect of re‐breeding attempts on estimations of the total breeding population. The model was used to simulate the consequences of adult mortality and different annual patterns of nesting failures on total breeding population estimates, and to explore the consequences of variation in p on N, when total breeding population remains constant. N is shown to be very sensitive to variations in p, so that even short‐term fluctuations in p can cause changes in N that oscillate for many years ahead. We compare our modelled results with real data for Grey‐headed Albatrosses Thalassarche chrysostoma and demonstrate that, when I is held constant in the model, actual counts may be simulated by variations in p only. Normally, I is unknown and is extrapolated from N on the assumption that N mirrors changes in the size of the total population. Consequently, applying average values of p can result in misleading estimates of total breeding population. We recommend that annual counts of breeding individuals are supplemented with annual estimates of p. Field protocols that aim to estimate annual breeding population size from counts of breeding individuals should be complemented by independent measures of rates of re‐breeding and nest failure.

Temporal shift in density dependence among North American breeding duck populations

Environmental perturbation can have a marked influence on abundance and trend in many animal populations, but information is scant on how numerical change relates to variability in density-dependent and density-independent processes acting on populations. Using breeding population estimates for 10 duck species from a survey area of approximately 2.2 million km2 in central North America (1955-2005), we compared population growth models and related parameters among species and across time. All duck species showed evidence of density-dependent growth, and the best-fit relationship between population growth (r(t)) and population size (N(t)) was linear or convex for all species. Density dependence and associated population parameters were not related to an index of species life history strategy. Reanalysis of segmented (1955-1979, 1980-2005) r(t) time series, where the truncation date coincided with a putative decline in wetland availability on breeding grounds, showed that density-dependent forces were weakened during the latter time segment. Additionally, in later years most populations experienced increased first-order autocorrelation in annual counts, decreased intrinsic growth rate, increased nonlinearity in the relationship between r(t) and N(t), increased equilibrium return time, and increased inter-species synchrony in numbers. Such changes were not closely related to species life history strategy or to shifts in mean population size, average trend, and estimated carrying capacity. We speculate that shifts in breeding duck habitat quality altered historical predator-prey dynamics in the system and thereby underlie observed dynamical changes. The paradoxical finding that population abundance and trend do not reveal shifts in population processes highlights the need to go beyond simple numerical assessment when evaluating population responses to environmental perturbation.

Body Mass of Lesser Scaup during Fall and Winter in the Mississippi Flyway

The combined continental breeding population of greater and lesser scaup (Aythya marila and A. affinis, respectively) in North America has declined markedly since the mid-1980s (Afton and Anderson 2001). Annual breeding population estimates have been consistently below the North American Waterfowl Management Plan (NAWMP) goal of 6.3 million scaup (United States Fish and Wildlife Service and Canadian Wildlife Service 1986), and the 2005 estimate was 46% below the NAWMP goal and the lowest on record (Wilkins et al. 2005). Afton and Anderson (2001) reported the overall decline in scaup may be driven primarily by reductions in the lesser scaup population. Multiple hypotheses have been posed to address the scaup population decline, which may be influenced by factors operating throughout the annual cycle and range of scaup (Austin et al. 2000, Afton and Anderson 2001). Anteau and Afton (2004) evaluated the spring condition hypothesis and reported nutrient reserves of female lesser scaup at spring stopover areas in the upper Mississippi Flyway and breeding areas in Manitoba, Canada, were lower in 2000 and 2001 than in the 1980s and reported that these nutrient reserves may impact female survival, breeding propensity, and reproductive success. However, body mass dynamics of fall migrating and wintering scaup have not been studied since the 1980s and early 1990s in the Mississippi Flyway, and investigations of body mass and nutrient reserves of lesser scaup are needed throughout the annual cycle and range of the species (Austin et al. 2000). Fall and winter body condition influences survival, physiological and behavioral events, and subsequent reproduction of waterfowl (Dubovsky and Kaminski 1994, Barboza and Jorde 2002). Nutrient reserves acquired from foods consumed on wintering and migrational areas can influence breeding propensity and reproductive performance of geese, some ducks, and other migratory birds (Ankney and MacInnes 1978, Alisauskas and Ankney 1992, Norris 2005), including lesser scaup that use lipids acquired during winter, spring migration, or on breeding areas for clutch formation (Esler et al. 2001). We collected lesser scaup during fall 1999–2000 and winter 2000–2001 from Manitoba, Canada, southward within the Mississippi Flyway to Louisiana, USA. Our objectives were to 1) estimate body mass of lesser scaup and analyze sex-specific variation in mass in relation to location of scaup collection, age, body morphometrics, and date of collection, and 2) compare our contemporary estimates of scaup mass to those from previous studies conducted at similar locations.

Status and distribution of wandering, black-browed and grey-headed albatrosses breeding at South Georgia

Long-term studies at Bird Island, South Georgia, show that numbers of wandering, black-browed and grey-headed albatrosses have been decreasing since the late 1970s. To determine the status of the total South Georgia population, all known colonies were censused in 2003/2004 using a combination of yacht-based digital photography and ground counts. The breeding population estimates from this census are 1,553 pairs of wandering albatross, 74,296 pairs of black-browed albatross and 47,674 pairs of grey-headed albatross. A 30% decline since 1984 was recorded for wandering albatross, and comparison of a sample of black-browed and grey-headed albatross colonies on the mainland of South Georgia photo-censused in both 1985/1986 and 2003/2004 indicates similarly substantial population declines. Unless these decreases can be halted or reversed, doubt will exist as to the long-term viability of these species of albatross at South Georgia.

Breeding numbers and population trends of Wedge-tailed Shearwater (Puffinus pacificus) and Black Noddy (Anous minutus) in the Capricornia Cays, southern Great Barrier Reef

Wedge-tailed Shearwaters and Black Noddies are the two numerically dominant seabird species found in the southern section of the Great Barrier Reef, Australia. This research provides baseline breeding population estimates for nine of 16 islands in the Capricornia Group over five years for Shearwaters (1996–2000) and four years for Noddies (1997–2000). With estimates of ∼302000 active breeding pairs of Black Noddies and ∼560000 breeding pairs of Wedge-tailed Shearwaters in the area, the research results have confirmed the importance of the Capricornia Group as a recognised breeding area for these birds.

Evaluation of Indicated Breeding Pair Criteria to Estimate Mallard Breeding Populations

Indicated breeding pair (IBP) criteria have been used since the 1950s to estimate breeding duck populations, yet few studies have evaluated these criteria for accuracy of population estimation. During spring aerial and ground surveys, observed pairs of ducks, lone males, and groups of 2-4 males are enumerated as IBPs, and assumed to reflect breeding pairs. We radiomarked and observed 36 paired and 44 unpaired male mallards (Anas platyrhynchos) in Manitoba in 1998 and Saskatchewan in 1999 to document their sociability and evaluate accuracy of IBP criteria. Paired male mallards occurred with their mates ≥54% of the time, whereas unpaired males occurred as lone males and in groups of 2-4 males 80% of the time from 21 April to 30 May. Based on these data, we calculated that mallard breeding populations in our study areas may be overestimated by approximately 7%. Inflated population estimates could promote underestimated production indices, overestimated fall population indices, and overly liberal harvest regulations. We suggest development of correction factors or modified survey criteria to improve accuracy of breeding population estimates for mallards and other duck species.

Breeding Cycle of Wedge-tailed ShearwatersPuffinus pacificusat Heron Island, Great Barrier Reef

Heron Island (23'27'S, 151°55'E), is a small coral cay of the southern Great Barrier Reef, one of several cays constituting the Capricorn Group of islands which supports a large breeding colony of Wedge-tailed Shearwater Puffinus pacificus. These birds excavate burrows for nesting in suitable ground, and nest colonially (Warham 1990). To date, only breeding population estimates, burrow incubation rates, and a preliminary investigation into hatching success have been made at this locality (Gillham 1963; Shipway 1969; Ogden 1979, 1994; Hulsman 1984a; Hill & Barnes 1989; Dyer 1992; Dyer & Hill 1992; Ogden 1994; Hill et al. 1995). This study was based at Heron Island during the 1993-94 breeding season and describes the timing of the breeding cycle, particularly the hatching and fledging phases.