Troglodytes Aedon Research Articles

Effects of Shiny CowbirdMolothrus bonariensisparasitism on different components of House WrenTroglodytes aedonreproductive success

Avian brood parasites, including cuckoos and cowbirds, have multiple negative effects on their hosts. We analysed the effects of Shiny CowbirdMolothrus bonariensisparasitism on different components (e.g. egg losses, hatching success, chick survival and nest abandonment) of House WrenTroglodytes aedonreproductive success. We also conducted an experiment to discriminate between two mechanisms that may reduce hatching success in parasitized clutches: lower efficiency of incubation due to the increase in clutch volume and disruption of host incubation by the early hatching of Cowbirds. Egg puncturing by Shiny Cowbirds reduced host clutch size at hatching by 10–20%, and parasitized nests had a decrease in hatching success of 40–80%. Egg losses and hatching failures were positively associated with the intensity of parasitism. Brood reduction was greater in parasitized nests, but the growth rate of the chicks that fledged was similar to that in unparasitized nests. The combined effects of egg losses, hatching failures and brood reduction decreased the number of fledged chicks by 80%. In addition, egg puncturing increased the likelihood of nest abandonment by Wrens. Experimental data showed that hatching failures occurred when there was a combination of: (1) an increase in the volume of the clutch by the addition of the Cowbird egg without removal of host eggs, and (2) the addition of the Cowbird egg before the onset of incubation. This was relatively common in House Wren nests, as Cowbirds generally parasitize before the onset of incubation. Our results indicate that Shiny Cowbird parasitism imposes a major impact on House Wrens, as it affects all components of the Wren's reproductive success.

Measuring egg size using digital photography: testing Hoyt's method using Florida Scrub-Jay eggs

Egg volumes are most often estimated using a mathematical model that incorporates length and width measurements and a species-specific shape variable. Although adequate in many respects, this technique does not account for intraspecific variation in egg shape. We developed a computer-automated technique that uses calibrated digital photographs to render precise measurements of several egg-size parameters including length, width, volume, and surface area. The system extracts egg outlines from photographs, and divides each egg into latitudinal slices that are subsequently regarded as simple geometric shapes (cylinders or cone frustra) with volumes and surface areas that can be summed to generate size parameters for the entire egg. We tested this technique using 491 eggs from Florida Scrub-Jay (Aphelocoma coerulescens) nests and compared the resulting egg volumes with volumes calculated using the preeminent method of estimating volume from linear measurements. Our method was highly accurate, and differences between the volumes from our method and the alternative method were strongly associated with variation in egg shape. Advantages of our technique include decreased handling of eggs and increased accuracy. Software resources and additional information regarding the technique are available at http://www.archbold-station.org/abs/data/birddata/Bridge-JFO-eggsize.htm. SINOPSIS. Medidas de huevos utilizando fotograf´ ia digital: poniendo a pruebas el m´ etodo

Eleven microsatellite loci isolated from the banded wren (Thryothorus pleurostictus)

We describe 11 microsatellite loci isolated from the Banded Wren (Thryothorus pleurostictus), a Neotropical species for which understanding the genetic mating system is important for testing questions about the species' unusual vocal behavior. Screening of these loci revealed extremely low allelic variation in a Costa Rican population. Allelic variation at these and other previously developed loci is substantially higher in two other wren species, the southern house wren (Troglodytes aedon bonariae) and rufous-and-white wren (Thryothorus rufalbus), suggesting that the low allelic diversity in the banded wren results from demographic bottlenecks rather than locus-sampling artifacts.

Mercury Exposure and Effects on Cavity-Nesting Birds from the Carson River, Nevada

Mercury (Hg) concentrations were 15-40 times higher in the eggs and livers of tree swallows (Tachycineta bicolor) and house wrens (Troglodytes aedon) that nested along the Carson River at and below Dayton, Nevada than in the same species above the mining-impacted areas. Hg contamination was mainly the result of processing mills in the 1800s that used Hg to separate gold and silver from ore. The exposure pattern of tree swallows and house wrens along the Carson River was consistent with their trophic status (i.e., lower levels in liver tissue of aquatic insectivores than in piscivorous birds nesting nearby). Even though they are aquatic insectivores, tree swallows and house wrens were exposed to the same amount of Hg as piscivores in the Florida Everglades; this indicated the extreme level of Hg contamination in the Carson River. Only 70-74% of the eggs hatched. This was less than the nationwide average for these two species that generally hatch > or =85% of eggs. Although the sample size was small, Hg might be impacting reproductive end points in cavity-nesting birds from the Carson River. Other trace elements were present at background concentrations.

Distribution and Relative Abundance of Forest Birds in Relation to Burn Severity in Southeastern Arizona

The frequency of wild and prescribed fires in montane forests of the southwestern United States has increased after a century of fire suppression and subsequent fuels accumulation. To assess the effects of recent fires (median time since fire = 6 yr) on the montane forest bird community, we surveyed birds in 8 Sky Island mountain ranges in southeastern Arizona, USA, and examined how the distribution (i.e., presence–absence) of 65 species and relative abundance of 16 species correlated with evidence of severe and less severe fire at >1,500 survey points. We detected associations between fire and bird presence–absence for 17% of the 65 species analyzed and between fire and bird relative abundance for 25% of the 16 species analyzed. Most species (73%) were positively associated with burned areas and displayed stronger associations (i.e., more extreme odds ratios) with survey points that had evidence of severe as opposed to less severe fire. Positive associations with severe fire were strong (>3 to 1 odds) for western wood-pewee (Contopus sordidulus) and house wren (Troglodytes aedon), and negative associations with severe fire were strong for warbling vireo (Vireo gilvus) and red-breasted nuthatch (Sitta canadensis). Although recent fires appear to have had a positive effect on the distribution and relative abundance of several montane forest bird species in the region, these species are not the open-woodland birds that we would have expected to have benefited from fire based on previous research. Nevertheless, our results confirm associations between fire and bird presence–absence and relative abundance reported previously for 7 species of birds. Our results also provide new information for Grace's warbler (Dendroica graciae) and greater pewee (C. pertinax), 2 species for which fire data were formerly lacking. Managers can use these data to make and test predictions about the effects of future fires, both severe and less severe, on montane forest birds in the southwestern United States.

Clutch size and the costs of incubation in the house wren

Trade-offs in the allocation of finite resources among different stages of a breeding attempt as well as between different reproductive events should shape the evolution of life-history traits. To investigate the effects of incubation effort on within-brood and between-brood trade-offs in house wrens (Troglodytes aedon), we manipulated the clutch size that females incubated. We isolated effects of incubation by reversing the manipulation at hatching to allow all parents to provision their natural brood sizes. Females that incubated enlarged clutches had longer incubation periods than control females, both early and late in the season, suggesting that the experimental treatment increased incubation effort. Contrary to predictions, however, increased incubation effort did not adversely affect the allocation of effort to nestling provisioning. Rather, in the early season, but not in the late season, females that incubated enlarged clutches appeared to allocate more effort to nestling provisioning, producing heavier and larger fledglings than control females. Although females with enlarged early-season clutches consequently lost more mass than control females, this was likely an adaptive response to reduce wing loading in anticipation of high provisioning demands. There were no treatment-related differences in fledgling mass or size, or in female mass loss, in the late season. Thus, elevated incubation demands negatively affected a fitness-related trait (duration of incubation) that may constrain clutch size but not the allocation of resources to subsequent stages of the same breeding event or to subsequent breeding events. We suggest that environmental conditions may mediate clutch-size effects on trade-offs in allocation of resources between incubation and nestling provisioning. Key words: clutch size, house wren, incubation, life history, trade-offs, Troglodytes aedon. [Behav Ecol]

Physiological and behavioural correlates of life‐history variation: a comparison between tropical and temperate zone House Wrens

1. We studied physiological, behavioural and demographic traits of House Wrens (Troglodytes aedon) in tropical Panama and temperate zone Ohio to explore the hypothesis that tropical birds with higher adult survival rates invest less in annual reproduction than their temperate zone counterparts. 2. Compared with wrens from Ohio, Panamanian wrens invested fewer resources in a given reproductive episode, as quantified by lower parental field metabolic rate (FMR) and water influx rate (WIR), a smaller number of feeding trips to the nest, and fewer chicks per brood. 3. Whole organism FMR and WIR were only 13-15% lower in tropical wrens, but because of their larger body size, mass-specific values were reduced by 34-37%. We propose that selection acts indirectly on whole-organism energy expenditure in the tropical wrens by specifically reducing mass-specific levels of metabolic rate, thereby postponing deleterious effects of aging and thus decreasing intrinsic mortality. 4. Declines in parental FMR and fledgling survival probability in the course of the season suggest that reproduction is more time-constrained in the temperate zone, compressed by the shorter breeding season, and as a result more energetically costly for the parents. In contrast, tropical wrens do not show temporal variation in FMR and nesting success and therefore are less constrained to breeding during a short season.

Accumulation of polychlorinated biphenyls from floodplain soils by passerine birds

Eggs, nestlings, and adults of the eastern bluebird (Sialia sialis) and house wren (Troglodytes aedon) were collected at a polychlorinated biphenyl (PCB)-contaminated site and a reference location on the Kalamazoo River (MI, USA). Eggs and nestlings of eastern bluebirds at the more contaminated location contained concentrations of 8.3 and 1.3 mg/kg, respectively, of total PCBs and 77 and 6.3 ng/kg, respectively, of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs). Eggs, nestlings, and adults of house wrens from the contaminated location contained 6.3, 0.77, and 3.2 mg/kg, respectively, of PCBs and 400, 63, and 110 ng/kg, respectively, of TEQs. Concentrations of total PCBs and TEQs in tissues at the more contaminated location were significantly greater than concentrations in tissues at the reference site for all tissue types of both species. Exposures of the two species studied were different, which suggests that terrestrial-based insectivorous passerine species, foraging in the same area, may have differential exposure to PCBs depending on specific foraging techniques and the insect orders that are targeted. Despite the greater accumulation of PCBs at the more contaminated location, the risk of exposure to PCBs did not exceed the threshold for adverse effects at either location.

Use of a new model to quantify compromises between embryo development and parental self-maintenance in three species of intermittently incubating passerines

1. Instead of just times to cool ( t cool) and heat ( t heat), intermittent incubation cycles contain a period ( t equil) when eggs are kept at relatively high equilibrium temperatures after heating. 2. Relative allocations favoring parental self-maintenance [when ( t cool+ t heat)> t equil] versus embryo development [when ( t cool+ t heat)< t equil] were measured for house wrens ( Troglodytes aedon), tree swallows ( Tachycineta bicolor) and black-capped chickadees ( Poecile atricapillus). 3. Wrens showed over-all significant relative allocation to parental self-maintenance, while chickadees and swallows balanced both functions. 4. House wrens gradually shifted allocation toward increased average egg temperature as incubation progressed, calling into question how temperature influences development rate.

Surplus nest boxes and the potential for polygyny affect clutch size and offspring sex ratio in house wrens.

Females of many species can gain benefits from being choosy about their mates and even exhibit context-dependent investment in reproduction in response to the quality of their breeding situation. Here, we show that if a male house wren is provided with surplus nest boxes in his territory, his mate lays a larger clutch with a significantly higher proportion of sons. This response to a territory characteristic directly associated with male competitive ability, and ultimately to male reproductive success, suggests that male competition over access to high-quality territories with surplus nest boxes (i.e. those able to support polygyny) may influence female reproductive investment decisions. The results of this study have interesting implications, particularly considering the important role that studies of cavity nesting birds utilizing nest boxes have played in advancing our understanding of behaviour, ecology and evolution.

External heart deformities in passerine birds exposed to environmental mixtures of polychlorinated biphenyls during development

Necropsy-observable cardiac deformities were evaluated from 283 nestling passerines collected from one reference site and five polychlorinated biphenyl (PCB)-contaminated sites around Bloomington and Bedford, Indiana, USA. Hearts were weighed and assessed on relative scales in three dimensions (height, length, and width) and for externally visible deformities. Heart weights normalized to body weight (heart somatic index) were decreased significantly at the more contaminated sites in both house wren (Troglodytes aedon) and tree swallow (Tachycineta bicolor). Heart somatic indices significantly correlated with log PCB concentrations in Carolina chickadee (Parus carolinesis) and tree swallow and with log 2,3,7,8-tetrachlorodibenzo-p-dioxin toxic equivalent values in tree swallow alone. Ventricular length was increased significantly in eastern bluebirds (Sialia sialis) and decreased significantly in Carolina chickadee and tree swallow from contaminated sites versus the reference site. Heart length regressed significantly against the log PCB concentrations (Carolina chickadee and tree swallow) or the square of the PCB concentrations (red-winged blackbird [Agelaius phoeniceus]) in a sibling bird. The deformities that were observed most at the contaminated sites included abnormal tips (pointed, rounded, or flattened), center rolls, macro- and microsurface roughness, ventricular indentations on the ventral or dorsal surface, lateral ventricular notches, visibly thin ventricular walls, and changes in overall heart shape. A pooled heart deformity index regressed significantly against the logged contaminant concentrations for all species except red-winged blackbird. These results indicate that developmental changes in heart morphometrics and shape abnormalities are quantifiable and may be sensitive and useful indicators of PCB-related developmental impacts across many avian species.

Mate choice in house wrens: nest cavities trump male characteristics

When male birds defend all-purpose breeding territories, females may select mates based on indicators of male or territory quality, or both. However, in non-experimental studies, it can be difficult to determine which traits females prefer because measures of male and territory quality frequently covary. We conducted a series of studies to investigate the traits female house wrens (Troglodytes aedon) use to select a social mate when each male is provided with nest sites of equal quality (i.e., nestboxes). We first compared the phenotypic and territory vegetation traits of males with the time it took them to secure a social mate after returning from the wintering grounds. Male arrival and pairing date were positively correlated and early-arriving males were in better condition and occupied territories in more preferred vegetation than late-arriving males. To test the hypothesis that early-arriving males possessed phenotypic or territory traits that led to their pairing more quickly than late-arriving males, we removed all females after pairs had been established and determined male success in attracting new mates. Male settlement and pairing date with replacement females were not correlated as had been male settlement and pairing date with original females, and male time-to-pairing was not correlated with male song rate, condition index, or territory vegetation. When we manipulated the abundance of nest sites on territories, after males settled but before females arrived, male time-to-pairing, independent of male condition index or territory vegetation, was negatively related to the number of nest sites on a male's territory. These results suggest that under natural conditions females rely on nest-site quantity and, likely, quality when selecting a social mate.

DEVELOPMENT OF VOCALISATIONS IN NESTLING AND FLEDGLING HOUSE WRENS IN NATURAL POPULATIONS

ABSTRACT We conducted a field study of the ontogeny of vocal signals in the house wren Troglodytes aedon during the nestling and fledgling phases of life. We did spectrographic analyses and quantification of the developmental changes that occurred in the acoustic features of the vocalisations. Evidence of progress to adult-like vocal patterns was of two types. First, nestling calls changed into a harsh-sounding call that resembles the adult chatter call, functionally a warning call. Second, fledglings also uttered subsong, and these vocalisations were similar to notes typical of adult male song. When the vocalisations produced by developing young were broken down into their constituent vocal features, we found that the time course of development was not strictly linear. Instead of a unidirectional change through the course of nestling and fledgling life, the trajectories of the vocal features fluctuated through time and sometimes exhibited abrupt changes. These sudden shifts occurred during nestling life as well as at the time of fledging. We speculate on the possible causes of these abrupt transitions. Changes in acoustic features upon fledging appear to be linked to new social functions.

Reproductive success of passerines exposed to polychlorinated biphenyls through the terrestrial food web of the Kalamazoo River

The eastern bluebird ( Sialia sialis) and the house wren ( Troglodytes aedon) were identified as ecological receptors of concern due to exposure and potential effects stemming from polychlorinated biphenyl (PCB) contamination in floodplain soils of the Kalamazoo River Superfund Site, Michigan, USA. Measures of population health were compared at a contaminated and a less-contaminated reference location. During this 3-year study, productivity of bluebirds was significantly less at the downstream location than at the reference location. Hatching success, clutch size, and predicted brood size were significantly less in early clutches of house wrens at the more contaminated location than at the upstream reference location, but fledging success was significantly greater at the contaminated location. Studies concurrent to the study presented here reported that concentrations of PCBs in the tissues and diets of the passerine birds were less than the predicted threshold for adverse effects. The results of our study, taken along with the measured exposure data, suggest that other factors in addition to PCB exposure such as habitat, prey availability, small sample size, and cocontaminants were likely causes of the differences that were observed at the two locations.

Avian Nest Box Use on Islands in the Ohio River

Abstract Although visibility of nest boxes may be important in nest-box selection for birds, there has been little investigation of this topic. Sixteen wooden nest boxes designed for passerines were placed on each of three islands (Middle, Buckley, and Muskingum) of the Ohio River in 2000, eight on the back channel side and eight on the navigational side. The objectives of this study were to determine the effects of nest-box placement and surrounding habitat characteristics on nest-box use. During the 2001 breeding season, birds used 74% of the nest boxes. Wren species had the highest use of nest boxes at 47.8%. Nests located in the least visible nest boxes were total moss nests (the combination of Parus carolinensis [Carolina Chickadee] nests and unidentified moss nests), whereas nests located in the most visible nest boxes were Troglodytes aedon (House Wren) nests and total wren nests. Nest boxes with southeastward orientations positively affected the placement of total moss nests and Carolina Chickadee...

Site Specific PCB-Correlated Interspecies Differences in Organ Somatic Indices

We correlated site specific differences in the organ somatic indices of nestlings of five passerine species (tree swallow, red-winged blackbird, house wren, Carolina chickadee, and eastern bluebird) with the degree of polychlorinated biphenyls (PCB) exposure in ovo and post-hatching. The birds were exposed to PCBs at or downstream of four PCB-contaminated sites. Of the organs evaluated for this paper, brain, bursa, heart, kidneys, lungs, pancreas, spleen, stomach, and thyroid varied significantly (p<0.05) or marginally significantly (0.05<p<0.11) between sites for at least one species. Differences were noted in the direction of the mean SI change (increased or decreased with increasing contaminant exposure by site) between different species for brain, lung, pancreas, spleen and thyroids. Our results indicated that no single passerine species fully represented the response characteristics observed in these species, and no single difference in organ SI should be used in ecotoxicological evaluations. Further, it is critical to include congener analysis in any evaluations since some endpoints in some species correlate well with total TEQs, and some with total PCBs and not TEQs. Some samples containing biologically significant levels of dioxin-like congeners would have been "non-detects" for total PCBs using common analytical methods.

Analysis methods for two types of second-order thermal transients

Methods are developed to find rate constants, asymptotes, and first derivatives of proportional temperature change at time zero for second-order transients when rate of change in core temperature initially is retarded or accelerated. Methods are applied to data for cooling chicken eggs (initially retarded core dynamics) and cooling 1-day-old nestling House Wrens in broods under natural conditions (initially accelerated core dynamics). Asymptotes minus T e are used to estimate an average net metabolic heat production rate of 0.016 W±0.0108 (S.D., n = 10 ) for 1-day-old House Wrens, a value similar to previous estimates using different methods.

New data on Philornis seguyi Garcia (1952)(Diptera, Muscidae)

Philornis Meinert is a very interesting Muscidae (Diptera) genus whose larvae are associated with a wide range of bird species. The existing description of Philornis seguyi Garcia (1952), which was reported in Argentina, so far involves only the female. During the 2000-2002 breeding seasons, we collected Philornis flies from six bird species in Buenos Aires province, Argentina. All the flies were identified as P. seguyi. Based on this material, we describe the larva, puparium, adult male, and male and female terminalia. All the host associations presented here--Mimus saturninus (Mimidae), Troglodytes aedon (Troglodytidae), Pitangus sulfuratus (Tyrannidae), Pyrocephalus rubinus (Tyrannidae), Satrapa icterophrys (Tyrannidae) and Molothrus bonariensis (Icteridae) in nests of M. saturninus and Troglodytes aedon--are new for P. seguyi. We also present some data on the biology of the species.

Sex manipulation within broods of house wrens? A second look

Most reports of adaptive manipulation of offspring sex in birds have come from single-year studies with relatively small sample sizes. Calls have thus gone out for repeat, multiple-year studies to confirm positive results. In a study of a Wyoming population of house wrens, Troglodytes aedon , Albrecht (2000, Animal Behaviour , 59 , 1227) asked whether embryos from last-laid eggs of clutches were predominantly female. Last-laid eggs typically hatch 36–48 h after most other eggs in the clutch. This puts offspring from last eggs at a competitive disadvantage and these offspring are often in poor physical condition at fledging. Albrecht argued that being in poor condition should negatively affect male fitness more than female fitness because males must compete for limited nest sites. Moreover, males that secure multiple sites have the potential to pair polygynously. Albrecht found a strong female bias among offspring from last-laid eggs (27 of 34 individuals) during the 1997 breeding season. We repeated Albrecht's study using the same population over three seasons, 2002–2004. We found no sex bias among offspring from last-laid eggs in any year; overall, 42 of 86 individuals (48.8%) were female. We also found no sex bias among offspring from second-to-last eggs, which also hatch late, or among offspring from the first two eggs. Why our findings differ from those of the original study is unclear. Nevertheless, we argue that whether (or when) house wrens adaptively manipulate the sex of offspring within broods must be considered an open question.

Differential Accumulation of Polychlorinated Biphenyl Congeners in the Terrestrial Food Web of the Kalamazoo River Superfund Site, Michigan

A series of field studies was conducted to determine the bioaccumulation of polychlorinated biphenyl (PCB) congeners in the terrestrial food web of the Kalamazoo River flood plain. Samples included colocated soils, native plants likely to be consumed by wildlife, several taxa of terrestrial invertebrates, small mammals, passerine bird eggs, nestlings, and adults, and great horned owl plasma and eggs. Mean concentrations of total PCBs in samples from the former Trowbridge impoundment were 6.5 mg/kg dry weight for soils and 0.023, 0.13, 1.3, 1.3, 1.6, and 8.2 mg/kg wet weight for plants, small herbivorous mammals, depurated earthworms, shrews, great horned owl eggs, and house wren eggs, respectively. Historical data from the Kalamazoo River have reported Aroclor-equivalent total PCB concentrations in the terrestrial food web; however, the degree of environmental weathering of the parent PCB mixtures was unknown. In this study, earthworms and composite samples of coleoptera exhibited PCB congener patterns that were similar to patterns in colocated soils. However, in plants, less chlorinated PCBs (e.g., mono-, di-, tri-, and tetrachlorinated biphenyls) were predominant, and in small mammals, there was a notable enrichment of PCBs 153, 180, 138, 118, and 99. In general, concentrations of PCBs were lower in most biota than in soil from the Kalamazoo River Area of Concern (KRAOC) although there was a modest biomagnification of PCBs from lower trophic level biota to highertrophic levels. As a consequence of environmental weathering of PCBs in the terrestrial food web of the KRAOC, the relative potency of the PCBs (expressed as mg TEQs/kg PCBs) decreased from soil to most biota. While there was a general trend, as expected, in which concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) increased with total PCBs, this relationship was rather poor (R2 = 0.13). Taken together, these data suggest that the differential accumulation of PCB congeners in the terrestrial food web can be explained by congener-specific differences in bioavailability from soil, exposure pathways, and metabolic potential of each of the food web components.