Erin A. Roche

Costs of Reproduction in Breeding Female Mallards: Predation Risk during Incubation Drives Annual Mortality

The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards, the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in terrestrial habitats. RESUME. L’effort investi a la reproduction peut avoir une incidence sur les couts futurs – comme un faible taux de survie ou de fertilite – et ces couts peuvent grandement influencer l’optimisation du cycle biologique. Chez les oiseaux dont les jeunes sont nidifuges, les couts hypothetiques de la reproduction sont surtout lies aux efforts nutritionnel et energetique investis dans la formation des œufs et a l’incubation. Dans le cadre de cette etude, nous avons mesure le taux de survie saisonnier de 3 856 Canards colverts (Anas platyrhynchos) femelles munies d’un emetteur radio, de leur arrivee sur les aires de nidification jusqu’a ce que l’elevage des jeunes soit complete ou jusqu’a l’echec de la nidification. Le taux de mortalite etait de 2,5 fois plus eleve chez les femelles qui couvaient leurs œufs en milieu terrestre, tandis qu’il a etait a son plus bas niveau saisonnier au moment de l’elevage des jeunes en milieu aquatique. Le taux de mortalite a aussi varie en fonction de la date : il etait a son maximum au moment ou de nombreux Canards colverts nichaient, ce qui laisse croire que le changement de proies dans la diete des predateurs communs pourrait exacerber le risque de mortalite chez les femelles a toutes les etapes de la nidification. Meme si les efforts investis dans la ponte et l’incubation ont eu un effet sur le taux de mortalite, la plupart des relations n’etaient pas conformes aux predictions de l’hypothese des couts de la reproduction; les femelles qui ont grandement investi dans la production d’œufs ou l’incubation ont eu un meilleur taux de survie, ce qui donne a penser que la variabilite de la qualite individuelle etait responsable des deux relations. Nous concluons que, chez les femelles nicheuses de Canard colvert, le cout principal de la reproduction est un cout fixe associe au risque de predation lie a l’incubation d’œufs en milieu terrestre.

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.

Spatial and temporal unpredictability of colony size in Cliff Swallows across 30 years

Most colonially breeding animals occupy colonies that range in size from a few pairs to thousands of individuals, but the causes of colony size variation are largely unknown. Three general hypotheses are: (1) that variation in colony size is maintained by fluctuating selection via spatial and temporal changes in fitness associated with different colony sizes; (2) that colony formation reflects heterogeneity in habitat, with some sites having resources to support more individuals than others; and (3) that individuals assess the presence or annual reproductive success of current colony residents at each site and aggregate preferentially at high-quality sites. These hypotheses make predictions about how consistent colony size should be across sites and among years. We examined temporal and spatial variability of colony size for >200 Cliff Swallow (Petrochelidon pyrrhonota) colony sites in western Nebraska across a 30-year period. A colonys substrate type, annual population size in the study area, and whethe...

Recapture Heterogeneity in Cliff Swallows: Increased Exposure to Mist Nets Leads to Net Avoidance

Ecologists often use mark-recapture to estimate demographic variables such as abundance, growth rate, or survival for samples of wild animal populations. A common assumption underlying mark-recapture is that all animals have an equal probability of detection, and failure to meet or correct for this assumption–as when certain members of the population are either easier or more difficult to capture than other animals–can lead to biased and inaccurate demographic estimates. We built within-year and among-years Cormack-Jolly-Seber recaptures-only models to identify causes of capture heterogeneity for a population of colonially nesting cliff swallows (Petrochelidon pyrrhonota) caught using mist-netting as a part of a 20-year mark-recapture study in southwestern Nebraska, U.S.A. Daily detection of cliff swallows caught in stationary mist nets at their colony sites declined as the birds got older and as the frequency of netting at a site within a season increased. Experienced birds’ avoidance of the net could be countered by sudden disturbances that startled them into a net, such as when we dropped a net over the side of a bridge or flushed nesting cliff swallows into a stationary net positioned at a colony entrance. Our results support the widely held, but seldom tested, belief that birds learn to avoid stationary mist nets over time, but also show that modifications of traditional field methods can reduce this source of recapture heterogeneity.

Female site familiarity increases fledging success in Piping Plovers (Charadrius melodus)

ABSTRACT. Reproductive success commonly improves with age in birds. However, it is difficult to determine whether this phenomenon is due to breeding experience or other age-related factors because most potential explanatory factors are positively correlated. Using a 17-year database, we investigated how age, breeding experience, location experience, and pair-bond experience influenced Piping Plover (Charadrius melodus) reproductive success in the Great Lakes region. Reproductive success was measured as number of offspring fledged per pair for 415 successful nests during 1993–2009. We controlled for individual and site variation with random effects and tested for increased reproductive success associated with age, prior breeding experience, prior location experience, and prior pair-bond experience using generalized linear mixed models. Reproductive success increased with location-specific breeding experience of females and declined when females moved to a new location. After statistically controlling for these effects, we found no additional effect of male age, male experience, or pair experience. Additionally, fledging success declined with later hatching dates, so we examined the relative influence of age and experience on hatch date and determined that older females and males bred earlier. Our results indicate that improvement in reproductive success with age in Piping Plovers has two components: a direct effect of female location experience on fledging success, and an indirect effect of timing of breeding, which leads to greater reproductive success through earlier nesting by older males and females. Actions by resource managers to promote breeding philopatry and successful early nesting attempts may enhance reproductive success of this federally endangered population.

Flooding Affects Dispersal Decisions in Piping Plovers (Charadrius melodus) in Prairie Canada

ABSTRACT. Flooding can cause widespread nest failure and chick mortality in sandbar-and beach-nesting waterbirds, particularly when human activity has either altered natural hydrology or limited available nesting habitat. Such widespread reproductive failure could increase breeding-season dispersal, leading to the abandonment of established nesting sites. We examined how annual movement &psgr; varied by sex, reproductive success, and flooding in three Piping Plover (Charadrius melodus) breeding areas in Saskatchewan during 2002–2009, using a multistate capture-mark-recapture model in Program MARK (n = 782). On average, female Piping Plovers were twice as likely as males to disperse and both sexes were more likely to disperse following years of poor versus moderate reproductive success (minimum to maximum values: &psgr;no-fledglings, 0.0054–0.0998 vs. &psgr;two-fledglings, 0.0017–0.0607). In addition, breeding Piping Plovers exhibited higher dispersal following flood years, even in years of moderate reproductive success (minimum to maximum values: &psgr;males-flood, 0.0025–0.0653 vs. &psgr;males-noflood, 0.0019–0.0399; and &psgr;females-flood, 0.0092–0.1089 vs. &psgr;females-no flood, 0.0070–0.0666). Consecutive floods could force Piping Plovers to nest at artificially high densities in new habitats that may be ill-suited to reproductive success. Given the benefits of site familiarity to reproductive success and survival, we recommend that conservation planning consider dispersal of breeding adults, in addition to nests and chicks, when water levels are managed at nesting locations used by Piping Plovers.

Fluctuating survival selection explains variation in avian group size

Significance A characteristic feature of animal groups is extensive variation in size. Biologists have recognized that group size can often have profound effects on the fitness of individuals, and often certain group sizes afford greater short-term benefits than others. When individuals in some group sizes are less successful, what maintains pervasive variation in group sizes in nature remains a fundamental problem in behavioral biology. In colonial cliff swallows, survival advantages regularly fluctuate among group sizes over time. This study shows that changes in the direction and form of natural selection on colony size serve to maintain a wide range of group sizes and represents the first case, to our knowledge, in which the advantages and disadvantages of different group sizes regularly fluctuate in a natural vertebrate population. Most animal groups vary extensively in size. Because individuals in certain sizes of groups often have higher apparent fitness than those in other groups, why wide group size variation persists in most populations remains unexplained. We used a 30-y mark–recapture study of colonially breeding cliff swallows (Petrochelidon pyrrhonota) to show that the survival advantages of different colony sizes fluctuated among years. Colony size was under both stabilizing and directional selection in different years, and reversals in the sign of directional selection regularly occurred. Directional selection was predicted in part by drought conditions: birds in larger colonies tended to be favored in cooler and wetter years, and birds in smaller colonies in hotter and drier years. Oscillating selection on colony size likely reflected annual differences in food availability and the consequent importance of information transfer, and/or the level of ectoparasitism, with the net benefit of sociality varying under these different conditions. Averaged across years, there was no net directional change in selection on colony size. The wide range in cliff swallow group size is probably maintained by fluctuating survival selection and represents the first case, to our knowledge, in which fitness advantages of different group sizes regularly oscillate over time in a natural vertebrate population.

Factors influencing nest survival and renesting by Piping Plovers in the Great Lakes region

ABSTRACT Renesting is an important breeding strategy used by birds to compensate for nest failure. If birds renest, clutch removal for captive rearing can be used to augment endangered populations; however, not all individuals renest following nest loss, and later nesting attempts may have lower survival rates and clutch sizes. We investigated variation in nest initiation date, clutch size, daily nest survival, renesting propensity, and renesting intervals of federally endangered Great Lakes Piping Plovers (Charadrius melodus) from 1993 to 2010. We also compared productivity under hypothetical clutch removal for captive rearing vs. non-removal scenarios. Nest initiation date was earlier for older adults and was more strongly affected by female than male age. Clutch size and nest survival decreased with later nest initiation, and nest survival increased with male age and nest age until close to hatching. Overall, Piping Plovers replaced 49% of failed nests. Renesting propensity decreased with later date, increased with each successive nesting attempt, and varied according to cause of failure; probability of renesting was highest following flooding and lowest for inviable clutches. Renesting intervals increased with age of the previous nest and averaged 4.2 days longer for birds that changed mates. Results also indicated that, compared to leaving eggs in situ, clutch removal for captive rearing would produce 43% fewer 1-year-old recruits, partly because renesting does not fully offset clutch removal; therefore, efforts to increase fledging success in this endangered population should focus on proactively protecting nests in situ rather than relying on collection of eggs for captive rearing.

The Effects of Sex, Age, and Social Status on Annual Survival in the Splendid Fairy-Wren

Abstract. Survival is a critical life-history trait, and among cooperative breeders survival may be linked to the evolution of social organization. We used multi-state models in the program MARK to estimate apparent survival in the Splendid Fairy-wren (Malurus splendens), a cooperatively breeding species in which most pairs are assisted by male offspring from previous generations. We examined survival as it relates to sex, age, and social status (nestling, auxiliary, breeder), and quantified the probabilities of transition between social states. The best-supported model was one in which survival rates differed by social state, survival of auxiliaries and breeders varied annually in the same manner, and the effect of sex varied annually but influenced the survival rate of each group in the same manner. In both males and females overall survival estimates of auxiliaries were similar to those of breeders, whereas survival estimates of adult males were higher than those of females, although the effect of sex varied annually. The probability of transition between categories of social status varied in a manner expected for a cooperatively breeding species: nestling males were more likely than nestling females to become auxiliaries, whereas females were more likely to become breeders in the subsequent year. Similarly, among auxiliaries, females were more likely than males to become breeders. Survival of males being higher that of females likely contributes to the male-biased sex ratio observed in adults of this species and, indirectly, the propensity of younger males to delay dispersal.