After-hatch-year Research Articles

Concentrations of Retinol and α-Tocopherol in Tissue Samples From Anna's Hummingbirds (Calypte anna).

Retinol (vitamin A) and α-tocopherol (vitamin E) concentrations were measured in tissue samples (liver, heart, pectoral muscle, and brain) from Anna's Hummingbirds (Calypte anna). Hummingbirds were after-hatch year birds that were sourced from various rehabilitation centers throughout California. Tissues samples were analyzed using high-performance liquid chromatography (HPLC). Minimum, maximum, mean, standard deviation (SD), and median ppm concentrations were calculated for each vitamin and tissue sample type. A novel analytical method was developed to analyze small mass tissue samples, with the smallest sample mass being 0.05 g for which analysis can be performed. Mean ± standard deviation (SD) concentrations of retinol in hummingbird livers, hearts, and pectoral muscle samples were 269.0 ± 216.9 ppm, 1.8 ± 2.2 ppm, and 0.3 ± 0.1 ppm, respectively. Mean ± SD α-tocopherol concentrations were 6.9 ± 4.6 ppm, 5.5 ± 4.0 ppm, 3.7 ± 2.2 ppm, and 9.1 ± 3.2 ppm for liver, heart, pectoral muscle, and brain samples, respectively. Vitamin concentrations from varying tissue types were compared to determine which were best associated with liver concentrations, the most commonly analyzed tissue for these vitamins. For both retinol and α-tocopherol, heart samples were most strongly associated with the liver samples. The results of this study provide baseline retinol and α-tocopherol concentrations in different tissue types from Anna's hummingbirds. These baseline values may be utilized in conservation efforts to avoid hypervitaminosis and hypovitaminosis of rehabilitated and/or captive hummingbirds by providing guidelines for nutritional targets which could be assessed on post-mortem examinations. Post-mortem examination of birds and measurement of vitamin concentrations in tissues may allow for dietary changes that aid captive hummingbirds.

After-hatch and hatch year Buff-breasted Sandpipers Calidris subruficollis can be sexed accurately using morphometric measures

After-hatch and hatch year Buff-breasted Sandpipers Calidris subruficollis can be sexed accurately using morphometric measures

Survival, Recovery, and Reproductive Success of Mottled Ducks on the Upper Texas Coast

Anas fulvigula (Mottled Duck) has experienced long-term population declines due to habitat loss and other anthropogenic factors. Our objectives were to (1) generate annual survival and recovery estimates, while examining the influence of age and sex, and (2) examine the influence of rainfall and drought on reproductive success. We followed the Brownie approach using the RMark package in R to analyze 4967 bandings and 705 recoveries from 2004–2015. We examined linear and curvilinear relationships between precipitation variables and a reproductive index. Hatch-year (HY) males had the highest annual recovery probability, while after-hatch-year (AHY) females had the lowest. Annual survival varied predominately by sex but also with age. Hatch-year females had the lowest estimate of survival, while after-hatch-year males had the highest. Total rainfall during peak nesting season showed a weak negative relationship with our reproductive success index (β = -0.0085, 95% CI: -0.0240, 0.0070), and was our only competitive model besides the null. Annual survival and recovery estimates were similar to other studies on Mottled Ducks. Our reproductive success analysis was inconclusive in that either there is no effect of precipitation or the measures we used for the reproduction index or the predictor variables were inadequate.

Age-Specific Differences in Fat Reserves and Migratory Passage ofSetophaga striata(Blackpoll Warbler)

Abstract Adequate fat reserves are vital for long non-stop transatlantic avian-migration movements, such as those made by Setophaga striata (Blackpoll Warbler). Over a 5-y period, we studied differences in preparedness (determined by presence of fat content and arrival time at stopover locations) between hatch-year (HY) and after hatch-year (AHY) Blackpoll Warblers at 3 stopover sites (Hancock and York counties in Maine, and Plymouth County in Massachusetts) covering 2.65° latitude along the Gulf of Maine. Migration timing varied across a latitudinal gradient and between age classes. In September, AHY Blackpoll Warblers were more abundant in the northern and central counties, but HY birds mostly passed through in October. Compared to AHY Blackpoll Warblers, our results suggest that HY birds migrated along a more northern route. After hatch-year birds had higher fat-content than HY birds at the northern and central sites. However, AHY birds had lower fat-content at the southernmost site. After hatch-year b...

Mourning dove period and annual survival in west‐central Missouri

ABSTRACTWe examined annual and period survival for mourning doves (Zenaida macroura) in Missouri, USA, using birds captured and marked on public land intensively managed for dove hunting. During 2005–2008, we radiomarked and monitored 713 birds to estimate period survival and banded 826 to estimate annual survival. For all ages, sexes, and years combined, spring‐summer survival prior to hunting season was 0.447 (95% CI = 0.378–0.517) and overall period survival during May–October, including hunting season, was 0.252 (95% CI = 0.200–0.303). Mean annual survival for after‐hatch‐year (AHY) doves was 0.214 (95% CI = 0.053–0.569) and 0.041 (95% CI = 0.002–0.506) for hatch‐year (HY) doves; recovery rates were 0.165 (95% CI = 0.105–0.249) for AHY and 0.179 (95% CI = 0.121–0.256) for HY doves. Our longer monitoring period allowed for a more robust picture of survival showing relatively low annual survival with few doves living beyond one year and significant mortality occurring prior to and during the hunting season. Differences in period survival each year likely reflect local differences in habitat influenced by weather and associated farming and management on the study area to attract feeding doves. Our results suggest locally intensive harvest management practices may be negatively affecting local populations and warrant continued monitoring to ensure long‐term population sustainability. © 2017 The Wildlife Society.

Using Banding and Encounter Data to Investigate Movements of Red-Tailed Hawks in the Northeastern United States

We examined encounter records from 1925 to 2015 for Red-tailed Hawks banded in the northeastern U.S.A. (n = 1002) and characterized movement patterns by evaluating straight-line distances, difference in latitude, and directionality between banding and encounter locations. We define “encounter” as any handling of a live banded bird, any recovery (a banded bird found dead), and any resighting (reading and reporting a band number on a live bird without actually handling the bird). The mean direction of all hawk encounters was to the southwest of banding locations but some hawks ranged widely; encounters occurred in 27 states, including some in the Mississippi flyway, and in four Canadian provinces. Hawks banded as nestlings or as hatch-year birds (younger) were encountered at farther distances and across a wider range of latitudes than hawks banded as after-hatch-year (AHY) or after-second-year (ASY; older). Most encounters were of younger hawks. In mid-century, most known mortalities were due to shooting; more recent mortalities were due to collisions with vehicles, buildings, or other objects. Some young hawks apparently dispersed out of their natal areas or began migration by three mo post-fledging, and hawks hatched in the Northeast apparently do not migrate north during their first summer. Hawks banded at higher latitudes were encountered at locations farther south than hawks banded at lower latitudes, substantiating leapfrog migration in this species. Encounter data suggested philopatric tendencies; hawks banded as nestlings and encountered at >46 mo of age were encountered significantly closer to their natal areas than hawks banded as nestlings and encountered 46 mo and >250 km from their natal area were considered long-distance dispersers. Between 1930 and 2010, for all hawks banded during the breeding season or summer and encountered in autumn or winter, the difference between banding latitude and encounter latitude decreased by about 4°, suggesting migratory short-stopping.

Demographic and Spatiotemporal Patterns of Avian Influenza Infection at the Continental Scale, and in Relation to Annual Life Cycle of a Migratory Host.

Since the spread of highly pathogenic avian influenza (HPAI) H5N1 in the eastern hemisphere, numerous surveillance programs and studies have been undertaken to detect the occurrence, distribution, or spread of avian influenza viruses (AIV) in wild bird populations worldwide. To identify demographic determinants and spatiotemporal patterns of AIV infection in long distance migratory waterfowl in North America, we fitted generalized linear models with binominal distribution to analyze results from 13,574 blue-winged teal (Anas discors, BWTE) sampled in 2007 to 2010 year round during AIV surveillance programs in Canada and the United States. Our analyses revealed that during late summer staging (July-August) and fall migration (September-October), hatch year (HY) birds were more likely to be infected than after hatch year (AHY) birds, however there was no difference between age categories for the remainder of the year (winter, spring migration, and breeding period), likely due to maturing immune systems and newly acquired immunity of HY birds. Probability of infection increased non-linearly with latitude, and was highest in late summer prior to fall migration when densities of birds and the proportion of susceptible HY birds in the population are highest. Birds in the Central and Mississippi flyways were more likely to be infected compared to those in the Atlantic flyway. Seasonal cycles and spatial variation of AIV infection were largely driven by the dynamics of AIV infection in HY birds, which had more prominent cycles and spatial variation in infection compared to AHY birds. Our results demonstrate demographic as well as seasonal, latitudinal and flyway trends across Canada and the US, while illustrating the importance of migratory host life cycle and age in driving cyclical patterns of prevalence.

Bill size correlates with telomere length in male American Redstarts

Telomere length (TL) has been shown to be a potential predictor of survival in wild vertebrates, and, as a consequence, there is growing interest in understanding the causes of inter-individual variability in TL. In that context, developmental conditions deserve a specific attention because they are thought to be a major driver of telomere shortening. Because poor developmental conditions can accelerate telomere shortening and impair growth (resulting in a small adult size), a positive correlation between TL and body size is expected. However, and surprisingly, the relationship between body size and telomere length has rarely been described in wild vertebrates. Here, we specifically examined this question in hatch-year (HY) and after hatch-year (AHY) male wintering American Redstarts (Setophaga ruticilla). Although tarsus size was not related to TL, we found a significant positive correlation between bill size and TL in HY male Redstarts, therefore supporting the idea that determinants of some components of individual size are also important determinants of TL in young birds. Moreover, this positive relationship between bill size and TL was also found for AHY birds, suggesting that adult TL may be, at least partly, explained by the telomere dynamics that occurred during the developmental phase.

Age-Related Differential Migration Strategies in Northern Saw-Whet Owls (Aegolius acadicus)

We analyzed differences in wing loading and body condition indices (BCI) between hatch-year (HY) and after-hatch-year (AHY) Northern Saw-whet Owls (Aegolius acadicus) captured during autumn migration in south-central Indiana. From 2002 to 2012, banders captured 1469 owls at two sites, including 826 HY owls and 641 AHY owls. The mean BCI (mass to wing chord ratio) was 0.665 g/mm and did not vary between HY and AHY owls. BCI was lowest in 2005 (0.658 g/mm) and highest in 2008 (0.679 g/mm). During autumn 2007, the banders photographed 267 owls at the two banding sites to enable comparisons of wing loading (mass to wing surface area ratio) and BCI for different age categories. Mean wing loading was 0.242 g/cm2 and also did not vary between HY and AHY owls, confirming the BCI results and suggesting that the age classes were not gaining or losing mass differentially. The median arrival date was 3 d earlier and the nightly median capture time was 10 min later for HY owls. In addition, the mass of HY owls correlated positively with the nightly capture time, whereas this was not true for adults. Together these results suggest that HY Northern Saw-whet Owls in south-central Indiana make up for any limitations in migratory/hunting abilities by migrating earlier each night and foraging more frequently while migrating. Migrating earlier, whether by choice or as a result of density-dependent adult competition, likely affords the younger birds greater access to prey in commonly exploited foraging areas. Available data indicate the potential for regional variation in the mass to wing chord correlation for this species, which needs further research. We also suggest that future studies obtain full wingspan measurements and compare the wingtip shape (amount of point and convexity) between juvenile and adult birds.Analizamos las diferencias en las cargas alares y los índices de condición corporal (ICC) entre el año de eclosión (AE) y después del año de eclosión (DAE) de individuos de Aegolius acadicus capturados durante la migración otoñal en el centro sur de Indiana. Desde el 2002 hasta el 2012 los ornitólogos capturaron 1469 lechuzas en dos sitios, incluyendo 826 lechuzas AE y 641 lechuzas DAE. La ICC media (el radio entre la masa y la cuerda alar) fue de 0.665 g/mm y no varió entre las lechuzas AE y DAE. El ICC más bajo ocurrió en 2005 (0.658 g/mm) y el más alto en 2008 (0.679 g/mm). Durante el otoño del 2007, los ornitólogos fotografiaron 267 lechuzas en los dos sitios de anillado para permitir comparaciones de cargas alares (radio entre la masa y la superficie alar) e ICC para diferentes categorías etarias. La carga alar media fue de 0.242 g/cm2 y tampoco varió entre las lechuzas AE y DAE, confirmando los resultados de los ICC y sugiriendo que las diferentes clases de edad no estuvieron ganando ni perdiendo masa de forma diferencial. La fecha de arribo mediana fue de 3 días antes y la hora de captura nocturna mediana fue de 10 minutos más tarde para las lechuzas AE. Además, la masa de las lechuzas AE se correlacionó positivamente con la hora de captura nocturna, mientras que esto no fue así para los adultos. Juntos, estos resultados sugieren que los individuos de A. acadicus del centro sur de Indiana compensan cualquier limitación en sus habilidades migratorias/de caza al migrar antes cada noche y al forrajear con mayor frecuencia mientras migran. La migración más temprana, por elección o como resultado de la competencia adulta dependiente de la densidad, probablemente le permite a las aves más jóvenes acceso a presas en áreas de forrajeo comúnmente explotadas. Los datos disponibles indican el potencial para una variación regional en la correlación de la masa y la cuerda alar para esta especie, aseveración que necesita de mayor investigación. También sugerimos que se obtengan en estudios futuros medidas de envergadura total y se compare la forma de la punta del ala (cantidad de punta y convexidad) entre aves juveniles y adultas.

PREVALENCE OF AVIAN PARAMYXOVIRUS 1 AND AVIAN INFLUENZA VIRUS IN DOUBLE-CRESTED CORMORANTS (PHALACROCORAX AURITUS) IN EASTERN NORTH AMERICA

Although it is well established that wild birds, such as cormorants, carry virulent avian paramyxovirus serotype 1 (APMV-1; causative agent of Newcastle disease) and avian influenza virus (AIV), the prevalence of these viruses among Double-crested Cormorants (Phalacrocorax auritus) in the Great Lakes region of North America has not been rigorously studied. We determined the prevalences of APMV-1 and AIV in Double-crested Cormorants from the interior population of eastern North America. From 2009 to 2011, oropharyngeal and cloacal swabs and serum samples were collected from 1,957 individual Double-crested Cormorants, ranging from chicks to breeding adults, on breeding colony sites in Michigan, Wisconsin, and Mississippi, USA, and Ontario, Canada, as well as on the wintering grounds of migratory populations in Mississippi, USA. Prevalence of antibodies to APMV-1 in after-hatch year birds was consistently high across all three years, ranging from 86.3% to 91.6%. Antibody prevalences in chicks were much lower: 1.7, 15.3, and 16.4% in 2009, 2010, and 2011, respectively. Virulent APMV-1 was detected in six chicks sampled in 2010 in Ontario, Canada. Only one adult was positive for AIV-specific antibodies and five individuals were positive for AIV matrix protein, but the latter were negative for H5 and H7 AIV subtypes. We provide further evidence that Double-crested Cormorants play an important role in the maintenance and circulation of APMV-1 in the wild, but are unlikely to be involved in the circulation of AIV.

Evaluation of the effects of september hunting seasons on Canada geese in Nebraska

AbstractPopulations of temperate‐nesting Canada geese (Branta canadensis) have increased in Nebraska, USA, resulting in an increased number of nuisance and damage complaints. September hunting seasons were initiated in southeastern Nebraska in 2004 to reduce populations of Canada geese. We analyzed band recoveries from Canada geese banded in southeastern Nebraska during their hatch‐year (HY) or after‐hatch‐year (AHY) to determine whether September hunting seasons affected survival, harvest, and recovery rates. Survival analyses revealed that HY geese had higher survival than AHY geese (SAHY = 0.696, 95% CI = 0.679–0.713; SHY = 0.896, 95% CI = 0.786–0.953) and September seasons did not affect survival of geese in southeastern Nebraska. Geese banded in the geographic zone with the September seasons (southeastern Nebraska) had the same survival as did geese outside the hunt zone (northeastern Nebraska; S = 0.711, 95% CI = 0.666–0.752). September hunting seasons affected timing of band recovery; 23–49% of annual band recoveries occurred during the month of September. Prior to the initiation of the September seasons, the highest percent of recoveries occurred during November. The September seasons appeared to temporally redistribute harvest but did not reduce survival for populations of Canada geese in southeastern Nebraska. Continuation of the season may not be warranted, because management does not appear to be affecting AHY survival, which is needed to reduce the population. Additional or new methods are likely needed to control populations of temperate‐nesting Canada geese in Nebraska and managers should evaluate the effectiveness of these methods as they are implemented. © 2012 The Wildlife Society.

Egg Oiling to Reduce Hatch-Year Ring-Billed Gull Numbers on Chicago’s Beaches During Swim Season and Water Quality Test Results

A burgeoning ring-billed gull population along Chicago's Lake Michigan beaches contributes to degraded water quality through fecal contamination. Egg oiling was conducted at Chicago's gull colonies to reduce production and the influx of hatch-year (HY) gulls using Chicago's beaches, with a second, long-term objective of eventually reducing adult gull numbers through attrition. We also investigated swim season water quality trends through the course of this work. From 2007 to 2009, 52, 80, and 81%, of nests at the two primary nest colonies had their eggs rendered inviable by corn oil application. Counts of HY and after hatch-year (AHY) gulls were analyzed during treatment years for 10 beaches. Water quality data were available from the Chicago Park District during our three treatment years and the prior year (baseline) for 19 beaches. HY counts declined at all 10 surveyed beaches from the initial year (52% nests with oiled eggs) to subsequent years with ~80% of nests oiled. Overall, HY gulls numbers on beaches decreased 86% from 2007 to 2009. Decreases in beach usage by AHY gulls were not detected. Compared to pretreatment, the number of beaches with improved water quality test rates increased each year through the course of the study. The frequency of water quality tests showing bacterial exceedances compared to 2006 declined at 18 of 19 beaches by 2009. Egg oiling resulted in fewer HY gulls using Chicago's beaches and was likely a beneficial factor for reduced frequencies of swim advisories and swim bans.

Demography and dispersal of juvenile and adult Brown-headed Cowbirds (Molothrus ater) in the eastern Sierra Nevada, California, estimated using multistate models

ABSTRACT. Despite recent progress in avian demography, much still needs to be learned about patterns of survival and dispersal across different ages and sexes of birds. This is expressly true for Brown-headed Cowbirds (Molothrus ater) in light of their vagility and importance in the life history of many other bird species. We used multistate mark—recapture models to estimate annual survival and dispersal rates of Brown-headed Cowbirds across dialect subpopulations in the Sierra Nevada of California across the 1982–1988 breeding seasons. We estimated rates for male and female hatch-year (HY) and after-hatch-year (AHY) birds and found no evidence of differences in capture probabilities across sex and age states. To account for high apparent nonresidency, adult survival was estimated separately for the year following initial capture and for subsequent years. The latter estimates are near the midpoint of those from other studies (AHY females: 56.1%; after-second-year [ASY] males: 63.4%; second-year [SY] males...

Female Harlequin Duck Winter Survival 11 to 14 Years After the Exxon Valdez Oil Spill

ABSTRACT In the mid‐ to late 1990s, nearly a decade after the 1989 Exxon Valdez oil spill, female harlequin ducks (Histrionicus histrionicus) suffered reduced winter survival in oiled areas of Prince William Sound, Alaska, USA, relative to unoiled areas. We conducted follow‐up studies from winters 2000–2001 to 2002–2003 to determine whether differential survival persisted and to evaluate whether individual‐level indices of oil exposure were related to survival. Using radiotelemetry, we tracked 138 female harlequin ducks from November through March over three winters. We analyzed variation in survival in relation to season, area oiling history, age class, body mass, and an index to exposure to residual oil based on cytochrome P4501A (CYP1A) induction. We determined that survival was most strongly related to season and age class, with evidence of higher survival in late winter and after hatch year (AHY) categories, respectively. We estimated cumulative winter survival for AHY females to be 0.837 (±0.064) and 0.834 (±0.065) on unoiled and oiled areas, respectively, and we estimated hatch‐year female cumulative winter survival at 0.766 (±0.138) on unoiled areas and 0.758 (±0.152) on oiled areas. Despite persistence of oil in some intertidal areas and evidence of contaminant ingestion by harlequin ducks during and beyond this study, neither area nor CYP1A were strongly related to variation in survival, suggesting that direct effects of the oil spill on harlequin duck demography had largely abated by the winters 2000–2001 to 2002–2003. Our findings offer an unprecedented description of the timeline of effects of exposure to spilled oil and contribute to a body of literature that describe demographic effects of the Exxon Valdez oil spill that persisted over a much longer time than previously assumed. An appreciation for the timescale of chronic effects of oil spills, as well as potential for demographic effects related to much lower concentrations of oil than during the immediate period of acute effects following a spill, will provide wildlife managers with a basis for risk assessment and plans for mitigation when confronted with large spills or chronic pollution.

Apparent survival, natal philopatry, and recruitment of Barrow’s goldeneyes (Bucephala islandica) in the Cariboo–Chilcotin region of British Columbia, Canada

We used capture–resight data to evaluate apparent survival, natal philopatry, and recruitment of Barrow’s goldeneyes ( Bucephala islandica (Gmelin, 1789)) in British Columbia, Canada. Median ages of first pairing and first breeding for females were 2 years and 3 years, respectively. The Cormack–Jolly–Seber model that best fit our data indicated that apparent survival rates (Φ) differed according to sex, year, and age class at marking. Estimates were similar for after-hatch-year (AHY) females (0.62) and AHY males (0.58), which was consistent with predictions. However, contrary to predictions, apparent survival rates of hatch-year (HY) females (0.68) were similar to those of AHY females and significantly higher than those of HY males (0.35). We interpret this difference as being primarily related to higher dispersal probabilities by HY males. Also evident was a negative correlation between apparent survival rate during the 1st year after capture for HY birds and their subsequent apparent survival rates, which suggests that probability of dispersal increased after these birds reached reproductive maturity and began to compete for breeding territories. We interpret this as evidence for density-dependent control of access to limited resources such as nest cavities.

Factors Affecting Body Condition of Northern Pintails Wintering in the Playa Lakes Region

We assessed the effects of capture period, capture subregion, age, sex and habitat conditions on the body condition of migrating and wintering Northern Pintails (Anas acuta) in the Playa Lakes Region (PLR) of northwestern Texas. Body condition varied with sex, age, subregion and month during the wet 2002. During 2002, after-hatch-year (AHY) males had more carcass fat (g and percent) than did AHY females. Likewise, AHY males had 34% more carcass fat (g) than hatch-year (HY) males, but we did not detect differences between AHY and HY females. The average increase in carcass fat (g) from October to November-December during wet 2002, was 26% for males and 42 to 93% (HY) for females. Body condition of pintails in the south exceeded those captured in northern subregions of the PLR during wet 2002, but not dry 2003. Southern caught AHY males had 31% more carcass fat (g) than northern caught AHY males, but we found no differences for HY males. Females caught in southern subregions also had 24–77% more carcass fat (g) than northern captured females. During dry 2003, pintail carcass fat (g and %) did not vary by capture location or among age and sex classes, except for males, which increased carcass fat by 34% between capture periods. From our findings, we recommend that managers periodically assess pintail body condition to detect temporal trends of condition status and measure population response to conservation efforts. However, use of body condition measures to evaluate habitat management and conservation efforts must be evaluated in the context of habitat conditions, sample locations, period of sample collection and age and sex classes.

Pintail and Mallard Survival in California Relative to Habitat, Abundance, and Hunting

ABSTRACT The influence of habitat, waterfowl abundance, and hunting on winter survival of waterfowl is not well understood. We studied late August‐March survival of 163 after‐hatch‐year (AHY) and 128 hatch‐year (HY) female mallards (Anas platyrhynchos) radiotagged in Sacramento Valley (SACV) and 885 AHY female northern pintails (A. acuta) radiotagged throughout the Central Valley of California, USA, relative to flooded habitat (HAB), January abundance of each species (JMAL or JPIN), hunter‐days (HDY), and a hunting pressure index (HPI) that combined these variables. From EARLY (1987–1994) to LATE (1998–2000), HAB increased 39%, JPIN increased 45%, JMAL increased 53%, HDY increased 21%, duck‐hunting season increased from 59 days to 100 days, and the female daily bag limit doubled to 2 for mallards but remained 1 for pintails. Survival (± SE) was greater during LATE versus EARLY for pintails radiotagged in each region (SACV: 93.2 ± 2.1% vs. 87.6 ± 3.0%; Suisun Marsh: 86.6 ± 3.2% vs. 77.0 ± 3.7%; San Joaquin Valley: 86.6 ± 3.1% vs. 76.9 ± 4.1%) but not for SACV mallards (AHY: 70.6 ± 7.2% to 74.4 ± 7.7% vs. 80.1 ± 7.2% to 82.8 ± 5.6%; HY: 48.7 ± 9.1% [1999–2000 only] vs. 63.5 ± 8.8% to 67.6 ± 8.0%). Most pintail (72%) and mallard (91%) deaths were from hunting, and lower HPI and higher JPIN or JMAL were associated with reduced mortality. Increased HAB was associated with reduced winter mortality for pintails but not for SACV mallards. Pintail survival rates that we measured were within the range reported for other North American wintering areas, and during LATE were higher than most, even though our study duration was 68–110 days longer. Winter survival rates of SACV mallards were also within the reported range. However, with higher bag limits and longer seasons, mallard survival during LATE was lower than in most other wintering areas, especially during 1999–2000, when high winds on opening weekend resulted in high hunting mortality. Habitat conservation and favorable agriculture practices helped create a Central Valley wintering environment where natural mortality of mallards and pintails was low and survival varied with hunting mortality. We recommend regulations and habitat management that continue to minimize natural mortality while allowing sustainable harvest at a level that helps maintain strong incentive for management of Central Valley waterfowl habitats, including the large portion that is privately owned.

NEST-SITE SELECTION OF PASSERINES: EFFECTS OF GEOGRAPHIC SCALE AND PUBLIC AND PERSONAL INFORMATION

Nest-site selection is an important determinant of individual fitness in birds. Understanding what information individuals use to choose nest sites is therefore important for understanding the evolution of nest-site selection, the dynamics of populations, and the conservation of species. We used five years of mark-recapture data for Mountain Bluebirds (Sialia currucoides) to examine how dispersal probability and nest-site selection vary with potential cues of nest-site quality. Dispersal distance between breeding seasons and nest-site selection were modeled as a function of personal reproductive success, conspecific density, conspecific reproductive success, and habitat type. Between years, the dispersal probability was related to personal reproductive success, not conspecific information, and individuals fledging fewer young dispersed longer distances. For dispersing individuals, the probability that a nest site was selected in year i was negatively related to distance from the nest site selected in year i - 1 for all age and sex classes, and positively related to conspecific density and reproductive success in year i - 1 for both second-year (SY) and after-hatch-year (AHY) females. However, nest-site selection in year i was more strongly related to conspecific density in year i- 1 for hatch-year (HY) females and was much more strongly related to the reproductive success of conspecifics in year i - 1 for AHY females. Nest-site selection of HY and AHY males was not consistently related to the metrics of conspecific information, but we suspect that relationships were obscured by competitive interactions. We found no evidence indicating that individuals respond differently to conspecific information at longer distances, suggesting that individuals limit dispersal to areas where they have prior knowledge. We predict that these patterns of nest-site selection will allow birds to loosely track nest-site quality and maintain an ideal free distribution, where average fitness is equal in all habitat types.

Vegetative and Fruit Resources as Determinants of Habitat use by Mature-Forest Birds During the Postbreeding Period

AbstractRecent studies have demonstrated that many birds of mature forests heavily use early-successional habitat during the postbreeding period. Two frequently invoked hypotheses to explain these shifts are that postbreeding birds select (1) dense cover to reduce risk of predation and (2) abundant fruit resources to facilitate foraging. Using mist nets between 15 June and 16 August in 2002 and 2003, we captured mature-forest birds during the postbreeding period in 12 regenerating hardwood clearcuts (three to seven years old) in southeast Ohio. Vegetation structure and fruit resources were measured at nine net locations within each clearcut. We applied an information-theoretic approach, where we used vegetative and fruit variables as predictors in seven a priori models to evaluate how habitat factors might explain capture rates. In two seasons, we captured 1,089 hatch-year (HY) and 445 after-hatch-year (AHY) postbreeding birds of 32 mature-forest species. In general, models reflecting habitat structure (density of low vegetation, canopy height) best explained variation in capture rates, which were negatively related to the density of low vegetation (<1.5 m) and positively related to canopy height. Extremely dense low vegetation may be disadvantageous if it inhibits movements and provides cryptic locations for ground predators. Instead, habitats with greater vertical structure (e.g., taller vegetation) and relatively less dense low vegetation below may provide better protection from aerial and ground predators. Overall, results suggest that vegetation structure may explain high use of early-successional forests by many birds during the postbreeding period, though fruit may be the most important factor for seasonal frugivores.Recursos Vegetativos y de Frutos como Determinantes del Uso de Hábitat por Aves de Bosque Maduro Durante el Período Posterior a la Reproducción

AGE RATIOS AS ESTIMATORS OF PRODUCTIVITY: TESTING ASSUMPTIONS ON A THREATENED SEABIRD, THE MARBLED MURRELET (BRACHYRAMPHUS MARMORATUS)

The ratio of hatch-year (HY) to after-hatch-year (AHY) individuals (HY:AHY ratio) can be a valuable metric for estimating avian productivity because it does not require monitoring individual breeding sites and can often be estimated across large geographic and temporal scales. However, rigorous estimation of age ratios requires that both young and adult age classes are sampled in an unbiased manner, an assumption that is rarely tested. We estimated HY:AHY ratios for Marbled Murrelets (Brachyramphus marmoratus), a threatened seabird, using at-sea surveys and captures to assess whether age-specific differences in behavior and distribution result in biased productivity estimates in central California. AHY and HY Marbled Murrelets were distributed similarly at sea, and HY individuals did not congregate in nursery areas. Moreover, dispersal by radiomarked AHY Marbled Murrelets out of our survey area occurred at a low rate, and AHY densities were constant over the survey period, which suggests that AHY immigration and emigration did not significantly bias productivity estimates. HY density increased linearly over the survey period as expected if little dispersal occurred, which suggests that productivity estimates were not significantly biased by HY dispersal. Finally, simulation analyses indicated that annual variation in the timing of breeding resulted in only small biases in HY:AHY ratios. HY:AHY ratios were corrected for the proportion of AHY Marbled Murrelets that were incubating and the proportion of HY individuals that had not fledged at the time of sampling. Mean corrected HY:AHY ratios were low on the basis of both at-sea surveys conducted from 1996 to 2003 (0.032; SE = 0.011) and captures conducted from 1999 to 2003 (0.037; SE = 0.028), implying that productivity was poor in central California. Estimating age ratios may be an effective way of monitoring changes in reproductive success and identifying environmental factors that affect Marbled Murrelet populations, though tests of assumptions are needed in other regions. Le Rapport des Âges comme Estimateur de la Productivité: Tester les Hypothèses avec un Oiseau de Mer Menacé, Brachyramphus marmoratus