Size-adjusted Mass Research Articles

Detection, prevalence, and transmission of avian hematozoa in waterfowl at the Arctic/sub-Arctic interface: co-infections, viral interactions, and sources of variation.

BackgroundThe epidemiology of avian hematozoa at high latitudes is still not well understood, particularly in sub-Arctic and Arctic habitats, where information is limited regarding seasonality and range of transmission, co-infection dynamics with parasitic and viral agents, and possible fitness consequences of infection. Such information is important as climate warming may lead to northward expansion of hematozoa with unknown consequences to northern-breeding avian taxa, particularly populations that may be previously unexposed to blood parasites.MethodsWe used molecular methods to screen blood samples and cloacal/oropharyngeal swabs collected from 1347 ducks of five species during May-August 2010, in interior Alaska, for the presence of hematozoa, Influenza A Virus (IAV), and IAV antibodies. Using models to account for imperfect detection of parasites, we estimated seasonal variation in prevalence of three parasite genera (Haemoproteus, Plasmodium, Leucocytozoon) and investigated how co-infection with parasites and viruses were related to the probability of infection.ResultsWe detected parasites from each hematozoan genus in adult and juvenile ducks of all species sampled. Seasonal patterns in detection and prevalence varied by parasite genus and species, age, and sex of duck hosts. The probabilities of infection for Haemoproteus and Leucocytozoon parasites were strongly positively correlated, but hematozoa infection was not correlated with IAV infection or serostatus. The probability of Haemoproteus infection was negatively related to body condition in juvenile ducks; relationships between Leucocytozoon infection and body condition varied among host species.ConclusionsWe present prevalence estimates for Haemoproteus, Leucocytozoon, and Plasmodium infections in waterfowl at the interface of the sub-Arctic and Arctic and provide evidence for local transmission of all three parasite genera. Variation in prevalence and molecular detection of hematozoa parasites in wild ducks is influenced by seasonal timing and a number of host traits. A positive correlation in co-infection of Leucocytozoon and Haemoproteus suggests that infection probability by parasites in one or both genera is enhanced by infection with the other, or that encounter rates of hosts and genus-specific vectors are correlated. Using size-adjusted mass as an index of host condition, we did not find evidence for strong deleterious consequences of hematozoa infection in wild ducks.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1666-3) contains supplementary material, which is available to authorized users.

Migration strategy predicts stopover ecology in shorebirds on the northern Gulf of Mexico

AbstractTwenty-eight species of migratory shorebirds rely on the coastlines of the northern Gulf of Mexico (NGOM) to fuel migrations to near-arctic breeding grounds. Shorebird species vary in their migration ecology: some species use a “jump” strategy, migrating long distances without stopping, while others use “skip” and “hop” strategies, stopping to refuel at shorter intervals along their journey. We compared stopover duration, body condition (fat scores and size-adjusted mass), and refueling rates (plasma metabolite concentrations), in three Calidrid sandpiper species (Calidris pusilla, C. mauri, and C. alpina) that differ in migration strategy after leaving the NGOM during spring. Results indicate that, while birds refueled at similar rates, C. alpina, an intermediate distance jump migrant, reached higher fuel stores before departing on migration than the hop and skip migrants, C. pusilla and C. mauri. C. alpina also spent more time on the NGOM than the other two species. Results suggest that NGOM habitats may be particularly important for migration success in C. alpina. This knowledge will help us predict the potential population level consequences of habitat loss due to global change on NGOM shorebird populations and develop conservation plans to mitigate these impacts.

Energetic Condition of Semipalmated and Least Sandpipers during Northbound Migration Staging Periods in Delaware Bay

Semipalmated and Least Sandpipers (Calidrispusilla, C. minutilla) were captured in Delaware Bay, USA, from 1995–1997 and from 2000–2008 to investigate changes in energetic condition during northbound migration staging. For Semipalmated Sandpiper, a model containing the effects of Julian day, period (Early: 1995–1997, Middle: 2000–2004, Late: 2004–2008) and habitat type (marsh, beach), as well as all interaction terms for these variables (the “full” model) had the strongest support (i.e. lowest AIC score) compared to six reduced models. Results suggested that mean size-adjusted mass declined significantly across periods (Early > Middle > Late). Also, rate of increase in size-adjusted mass within staging periods was significantly greater during the Early compared to Middle and Late periods. For Least Sandpiper, a reduced model that included Julian day and Period had the strongest support. Size-adjusted mass was significantly lower in the Late compared to Early and Middle periods, which were not different from each other. While in Delaware Bay, Semipalmated Sandpipers feed primarily on horseshoe crab eggs during episodes of rapid mass accumulation, but harvest pressure from 1995–2005 dramatically reduced egg availability. Least Sandpipers appear less dependent on this resource, which may explain differences between the two species regarding changes in energetic condition during staging periods in Delaware Bay. Long-term population trend indices suggest that Semipalmated Sandpiper has declined significantly since the 1980s, especially populations migrating along the Atlantic Coast en route to eastern Canadian breeding areas, which could be related, in part, to changes in food availability in Delaware Bay.

The Morphometrics of Migrant Semipalmated Sandpipers in the Bay of Fundy: Evidence for Declines in the Eastern Breeding Population

Over 16 field seasons, between 1981 and 2006, nearly 20,000 migrant Semipalmated Sandpipers were captured, weighed, and their bills and wings measured during the fall stopover in the Bay of Fundy. Annual mean bill and wing lengths declined over the course of the study. As eastern Semipalmated Sandpipers have longer bills and wings than those from the west, we interpret the decline to be the result of a reduced proportion of eastern birds in our samples. Semipalmated Sandpiper populations are in decline in North America, and our data suggest that the decline may be more severe in the eastern part of their breeding range. Body mass and size-adjusted mass at the migratory stopover study site have not declined during the study, suggesting that feeding conditions have not deteriorated there. Possibly, differing conditions experienced on the breeding grounds or overwintering areas may explain why eastern populations of Semipalmated Sandpipers may be declining more severely than those from the west.

Challenges In Creating An American Kestrel Body Condition Index Based On Size-Adjusted Mass

Abstract Size-adjusted mass is a common body condition index (BCI) used to indicate nonstructural energy reserves (fat and protein). BCIs are calculated from ratios of mass divided by a morphometric(s) or residuals of a regression between mass and a morphometric(s). The morphometrics used in BCIs must accurately represent structural size to reliably index energy reserves and, ideally, BCIs should be validated with comparisons to true fat and protein reserves. Many studies of American Kestrels (Falco sparverius) have included BCIs in ecological analyses; unfortunately, few studies have reported how well morphometrics represented structural size or provided validation of BCIs relative to independent measures of energy reserves. We evaluated relationships between several morphometrics and mass to better understand which morphometrics may best represent structural size for two kestrel populations: captive birds at McGill University in Montreal, Canada, and free-living kestrels in southwestern Idaho, U.S.A. We...

Spring Stopover and Refueling Among Migrant Passerines in the Sierra De Los Tuxtlas, Veracruz, Mexico

The narrowing of the North American continent at the Isthmus of Tehuantepec creates an important geographic bottleneck for songbirds on their northward spring migrations. The Sierra de Los Tuxtlas, in the northwestern portion of the Isthmus, provide an ideal location from which to address questions of resource use and fuel acquisition during migration. We operated mist nets during morning and evening to capture passerines during spring migration in 2003 and 2004. Seven of 13 taxa had significant diurnal increases in body condition (an index of size-adjusted mass): Swainson's Thrush (Catharus ustulatus), Wood Thrush (Hylocichla mustelina), Magnolia Warbler (Dendroica magnolia), Kentucky Warbler (Oporornis formosus), Hooded Warbler (Wilsonia citrina), Worm-eating Warbler (Helmitheros vermivorum), and Ovenbird (Seiurus aurocapilla). All of these species, except Ovenbird, also had a significant increase in fat score. Indigo Buntings (Passerina cyanea) had a significant increase in fat score but not in condition index. A comparison with autumn migration at this site showed overall similarities in percentage of species gaining mass and in the amount gained, but there were seasonal differences within species. There was no relationship between increase in body condition and a mainland versus trans-gulf migratory strategy.

Variation in Plumage Coloration of Northern Cardinals in Urbanizing Landscapes

Abstract Biologists know relatively little of how one of the most important avian phenotypic signals, feather coloration, may be affected by anthropogenic changes resulting from urbanization. We examined the relationship between urbanization and carotenoid-based plumage color of Northern Cardinals (Cardinalis cardinalis) in 13 riparian forests distributed across a rural-to-urban landscape gradient in central Ohio, USA. Feathers and morphometric measurements were collected from breeding territorial males (n = 129) and females (n = 145) during March–August 2006–2008. Plumage brightness of males, but not females, increased with body condition (i.e., size-adjusted mass) and declined with amount of urbanization surrounding forests in which cardinals bred. The extent plumage coloration reflected condition was partially mediated by landscape composition. Specifically, the relationship between brightness and body condition was most pronounced in the most rural landscapes. The interdependency of male coloratio...

Survival of postfledging Forster’s terns in relation to mercury exposure in San Francisco Bay

We examined factors influencing mercury concentrations in 90 fledgling Forster's terns (Sterna forsteri) and evaluated whether mercury influenced postfledging survival in San Francisco Bay, California. Mercury concentrations (+/- SE) in chicks 21-29 days old (just before fledging) were 0.33 +/- 0.01 microg g(-1) ww for blood and 6.44 +/- 0.28 microg g(-1) fw for breast feathers. Colony site had an overriding influence on fledgling contamination, however hatching date and age also affected blood, but not feather, mercury concentrations. Blood mercury concentrations decreased by 28% during the 50-day hatching period and increased with chick age by 30% during the last week prior to fledging. Using radio-telemetry, we calculated that cumulative survival during the 35-day postfledging time period was 0.81 +/- 0.09 (SE). Postfledging survival rates increased with size-adjusted mass, and cumulative survival probability was 61% lower for terns with the lowest, compared to the highest, observed masses. Conversely, survival was not influenced by blood mercury concentration, time since fledging, sex, or hatch date. Mercury concentrations in breast feathers of fledglings found dead at nesting colonies also were no different than those in live chicks. Our results indicate that colony site, hatching date, and age influenced mercury concentrations in fledgling Forster's terns, but that mercury did not influence postfledging survival.