Francesca J. Cuthbert

Uncertain nest fates in songbird studies and variation in Mayfield estimation

Abstract Determining whether nesting attempts are successful can be difficult. Yet, current protocols for estimating nesting success do not address how uncertain nest fates should be handled. We examined the problem of nest-fate uncertainty as it relates to Mayfield estimation of nesting success and in analyses of factors that influence success. We used data from Minnesota to illustrate the potential effect of uncertain fate; 40% of Ovenbird (Seiurus aurocapillus; n = 127) nests and 30% of Least Flycatcher (Empidonax minimus; n = 144) nests had uncertain fates. How this uncertainty is incorporated into Mayfield estimates of success varied widely among researchers. In a survey of researchers who use the Mayfield method, 9 of 22 respondents (of 40 contacted) excluded nests with uncertain fate. Excluding uncertain fates is counter to how Mayfield first described his estimator and can result in severe downward bias. The remaining respondents (59%) included nests with uncertain fate but varied in how they terminated the exposure period. We developed a simulation model that calculated Mayfield estimates using different approaches and compared them with a known rate of nesting success. Magnitude of bias in Mayfield estimates varied considerably in our simulations. The approach with the least bias terminated exposure with the last observed active date for nests with uncertain fate, and with the midpoint between last observed active and first observed inactive dates for nests with known fate. In addition, information necessary to interpret and compare Mayfield estimates often is not reported. These values, including variance estimates and the period lengths used to estimate survival rates, should be reported with Mayfield estimates. Finally, nest fate is commonly used as a categorical variable in studies of factors affecting nesting success. In this approach, however, nests with uncertain fate must be excluded. An alternative approach is Cox regression, which incorporates nests with uncertain fate.

EDGE EFFECT ON NESTING SUCCESS OF GROUND NESTING BIRDS NEAR REGENERATING CLEARCUTS IN A FOREST-DOMINATED LANDSCAPE

Abstract Forest fragmentation has been implicated as a cause of population declines of several Neotropical migrant bird species. Fragmentation increases the amount of habitat edge, and reduced nesting success rates near forest edges are well documented in agricultural landscapes (“edge effects”). However, edge effects in predominantly forested landscapes, particularly those related to timber harvest, are poorly understood. This study examines nesting success of ground nesting birds in relation to clearcut edges in a forest-dominated landscape in north-central Minnesota. A total of 383 nests of seven species of ground nesting birds were found and monitored during 1992–1998. Ovenbird (Seiurus aurocapilus; n = 318) and Hermit Thrush (Catharus guttatus; n = 44) nests composed the majority of the sample. Predation accounted for 94% of all nest failures. Brown-headed Cowbird (Molothrus ater) parasitism was low (1.8% for all ground nests). Using proportional hazards regression, distance to nearest clearcut edge was the best predictor of nest failure. For all ground nests, nesting success was 0.18 at 0–100 m, 0.39 at 101–500 m, and 0.52 at 501–954 m from nearest clearcut edge. Source–sink modeling indicated that distances ≤100 m from clearcut edges were sink habitats for Ovenbirds (i.e. recruitment was lower than survival). These results provide strong evidence of a negative edge effect on ground nests, extending 100 m or more from clearcut edges in a forest-dominated area of north-central Minnesota.

Historic Populations of the Double-crested Cormorant (Phalacrocorax auritus): Implications for Conservation and Management in the 21st Century

Abstract In North America, the Double-crested Cormorant (Phalacrocorax auritus) is currently abundant, widely distributed across five broad geographic regions, and often perceived as overabundant. In many U.S. states and Canadian provinces, policy makers are pressured to significantly reduce cormorant numbers, primarily to minimize conflicts between cormorants and fish resources. Concurrently, large-scale conservation plans recently developed for birds in the Americas depart from the traditional narrow focus on threatened and endangered species to encompass broader and more representative goals (e.g., Partners in Flight’s objective to “keep common birds common”). In recent waterbird conservation initiatives, historic distribution and abundance provide the basis for conservation focus; these initiatives advocate conservation of birds in natural numbers and natural habitats. To provide a context in which current populations of Double-crested Cormorants can be understood, we reviewed historic and current breeding and wintering records to determine historic distribution (pre-1900), current distribution (1970-1999), and extent of range expansion across North America. Early records suggest Double-crested Cormorants were present in large numbers throughout much of their current range; colonies and flocks much larger than any known in the 1990s are well documented. However, numbers sharply declined through the late 1800s as cormorants were greatly reduced and/or extirpated in many areas. The population partially recovered through at least the mid-1900s, but experienced a second major decline during the 1950s-1970s. In the late 1970s, a second rebound began across much of the continent; the largest breeding populations (Canadian/U.S. interior, Atlantic Coast >80% of total) increased from approximately 32,000 pairs in the early 1970s to >226,000 pairs in the late 1990s. Comparison of historic and current records challenges the opinion that cormorants are currently overabundant, and suggests that perception of overabundance rests on socio-political rather than biological or ecological factors. For this species, and others that are seen as competitors with humans, limits of human tolerance (i.e. “social carrying capacity”) are far narrower than those of biological carrying capacity. Because large numbers have been typical for cormorants historically, population targets based on fishery or other objectives derived from human values will likely be readily surpassed, require intensive management, and significantly depart from the concept of conserving birds in natural numbers and natural habitats. Although managing fish-eating birds to benefit fishery yields may increase some fish populations, this approach does not resolve or address the underlying problems causing current fish population declines across the continent, and is in direct conflict with current broad scale conservation initiatives. To ensure inclusion of cormorants and other fish-eating birds in these conservation plans, the avian conservation community must continue to press for programs based on ecosystem health and process that recognize humans, fish and cormorants as three components of a complex system driven by many species and dynamic interactions.

Influence of food distribution and predation pressure on spacing behavior in palm civets

The common palm civet, Paradoxurus hermaphroditus , was studied in Royal Chitwan National Park, Nepal, to determine daily and seasonal movements in relation to availability of food and predation pressure. Five adult animals (two females and three males) were captured and fitted with radiocollars and located every other day. Each animal was followed for 12 consecutive h/month. Palm civets were strictly nocturnal; activity began at ca. 1800 h and ended at ca. 0400 h. Animals were more active on dark nights than on bright, moonlit nights and typically rested during the day in the crown of vine-covered trees. Seeds of fruits were found in 84.5% of 193 scats of palm civets that were collected December 1989 to June 1990. In April, when ripe fruits were not readily available, a shift in diet from fruits to vertebrate and invertebrate prey occurred. Palm civets also fed on the nectar of Bombax ceiba and sap from stems of Vallaris solanacea . Home-range sizes varied inversely with the amount of food available. A high degree of home-range overlap indicated that individuals were not territorial. Documented predation and exclusive nocturnal activity suggest that palm civets are vulnerable to predation by large carnivores in the park. Strong predation pressure and high temporal and spatial variation in availability of food resources may account for the apparent absence of territorial behavior of palm civets in this population.

A COMPLETE SPECIES CENSUS AND EVIDENCE FOR REGIONAL DECLINES IN PIPING PLOVERS

Abstract Complete population estimates for widely distributed species are rarely possible. However, for the third time in 10 years, an International Piping Plover (Charadrius melodus) Breeding and Winter Census was conducted throughout the species range in 2001. Nearly 1,400 participants from 32 U.S. states and Puerto Rico; 9 Canadian provinces; St. Pierre and Miquelon, France; Cuba; and the Bahamas visited 2,244 sites covering 11,836 km of shoreline habitat. During the winter census, 2,389 piping plovers were observed at 33.5% of potentially occupied sites (n = 352). Of these, 56.8% had ≤ 10 birds present. The breeding census recorded 5,945 adults at 777 of 1,892 sites surveyed. More than 80% of sites with piping plovers present had ≤ 10 birds. Results indicated an 8.4% increase from 1991 but only a 0.2% increase since 1996. Regional trends suggest that since 1991, number of breeding birds increased on the Atlantic Coast by 78% (2,920 birds; 12.4% increase since 1996) and by 80% in the Great Lakes (72 birds; 50% increase since 1996). However, plovers declined 15% (2,953 birds; 10% decline since 1996) in Prairie Canada/U.S. northern Great Plains. Subregional trends since 1991 reflect a 32.4% decline in Prairie Canada (972 birds; 42.4% decline since 1996), a 2.5% decline in the U.S. northern Great Plains (1,981 birds; 24% increase since 1996), 5.5% decline in eastern Canada (481 birds; 14% increase since 1996), although a 66.2% increase on the U.S. Atlantic Coast (2,430 birds; 12% since 1996). While numbers were down in much of the U.S. northern Great Plains since 1996, an increase (460%, 1,048 birds; 67.7% increase since 1991) was detected on the Missouri River. Results from 3 complete species census efforts provide essential data for conservation planning and assessment and illustrate the utility of global censuses for species of concern.

Mate retention in caspian terns

Observation de colonies des Sterna caspia au nord-est du lac Michigan: des facteurs autres que le succes reproducteur anterieur influencent le choix du partenaire et la fidelite vis-a-vis de lui

Potential Impacts of Nesting Double-crested Cormorants on Great Blue Herons and Black-crowned Night-herons in the U.S. Great Lakes Region

Abstract With recovery of double-crested cormorants ( Phalacrocorax auritus ) in the Great Lakes region, their numbers have increased significantly leading to concern about potential impacts on other species. Cormorants are thought to affect co-occurring colonial waterbirds by usurping limited habitat and destroying vegetation used as nest sites by these species. This paper summarizes initial results from a study to assess potential impacts of double-crested cormorants on great blue herons ( Ardea herodius ) and black-crowned night-herons ( Nycticorax nycticorax ) in the Great Lakes. The study examined population trends, interspecific interactions, and cormorant impacts on vegetation. Despite a steady increase in breeding cormorants in the U.S. Great Lakes over the past two decades, population trends of great blue herons and black-crowned night-herons do not indicate cormorants have negatively influenced breeding distribution or productivity of either species at a regional scale. Cormorants have caused total or partial loss of forest cover at a number of islands in the U.S. Great Lakes and these initial data suggest soil chemistry at cormorant colony sites will affect normal plant growth and survival. However, site use data and field observations indicate double-crested cormorant presence has not caused black-crowned nightheron or great blue heron declines or abandonment except under special circumstances. Although preliminary, these results suggest cormorant control policy should not be justified by assumption of potential impacts on other waterbird species without careful documentation.

A habitat-based population model for the Great Lakes population of the piping plover (Charadrius melodus)

We created a stochastic habitat-based population model to compare the relative effectiveness of potential conservation strategies to increase the endangered Great Lakes population of piping plovers. Initial model parameters were based on an extensive 14-year dataset obtained by annual studies of breeding pairs in Michigan and 6 years of observations of color-marked individuals. Cumulative persistence probability curves and population trends were compared for scenarios with all possible combinations of the following: (1) empirical, medium and high site specific probabilities of reproductive success and (2) empirical, medium and high numbers of available breeding territories. Sites were also categorized according to land ownership to determine if long-term preservation of publicly owned lands is sufficient for population recovery under any of the scenarios. Only scenarios in which both reproduction and habitat availability were high and all ownership classes were included resulted in a model population that persisted for 100 years and was likely to reach the US Fish and Wildlife Service current population recovery goal (100 breeding pairs) for Michigan. The model was most sensitive to survival rates of adults and more sensitive to changes in reproductive parameters than to number of breeding sites or territories. Model results suggest that intensive measures to increase productivity alone are not sufficient for population recovery; increases in nesting densities or total number of available territories are also likely necessary. Given uncertainties about nesting densities possible at specific breeding sites, preservation of presently unoccupied habitat throughout the Great Lakes region and management of this habitat to encourage breeding by plovers are recommended. Use of techniques to augment the breeding population in conjunction with protection of habitat and reproduction may be warranted.

Apparent Nest Abandonment as Evidence of Breeding-Season Mortality in Great Lakes Piping Plovers (Charadrius melodus)

ABSTRACT. Abandonment was the most frequent cause of nesting failure in Great Lakes Piping Plovers (Charadrius melodus) during 1993–2007, and observations of color-banded adults suggested that most abandonments involved disappearance of attendant adults rather than behavioral decisions by adults to desert their nests. The purpose of our study was to integrate nest-monitoring histories with mark—resighting analyses to determine whether nest abandonment indicated adult mortality or nest desertion. Nesting Piping Plovers had extremely high within-year resighting probabilities (10-day mean p = 0.908 ± 0.025 [SE] ), and cumulative probabilities of being detected approached 1 for individuals that were present on the breeding grounds for ≥20 days post-abandonment. These observations suggested that desertion would be readily identified unless Piping Plovers left the monitoring areas immediately after deserting their nests. None of the 31 that disappeared (as indicated by nest-monitoring histories) was ever observed again, and an among-year mark—resighting analysis suggested that all had died. From 2002 to 2007, annual mortality associated with disappearances averaged 5.7% of the marked population. Disappearances occurred primarily from 16 May to 19 June, were more common among females, involved individuals that were older than average, and were most frequently attributed to predation by Merlins (Falco columbarius). Our results reveal that most early-season nest abandonment in Piping Plovers was attributable to the death of attendant adults. We believe that this phenomenon may be widespread among other species of birds in which adults are vulnerable to mortality during nesting.

Range-Wide Piping Plover Survival: Correlated Patterns and Temporal Declines

Abstract Geographically isolated breeding populations of migratory shorebirds may be demographically connected through shared nonbreeding habitats. We used long-term (1998–2008) mark–recapture data on piping plovers (Charadrius melodus) collected from 7 separate studies located throughout North America to conduct a range-wide analysis of after hatch year apparent survival (ΦAHY). Our objectives were to compare concurrent survival estimates from disparate breeding sites and determine whether estimates followed similar trends or were correlated among breeding populations with shared wintering grounds. Average survival estimates were higher for Great Plains populations (range  =  0.69–0.81) than for Great Lakes and Atlantic Coast populations (range  =  0.56–0.71). Linear trend models indicated that apparent survival declined in 4 out of 7 populations, was unchanged in 3, and was generally highest among Great Plains populations. Based on a post hoc analysis, we found evidence of correlated year-to-year fluctuations in annual survival among populations wintering primarily along the southeastern United States Atlantic Coast and Gulf Coast. Our results indicate shared overwintering or stopover sites may influence annual variation in survival among geographically disparate breeding populations. Declines in piping plover survival are a cause for concern, and our results highlight the need for conservation efforts to include habitat used during the migratory and wintering periods.