Nestling Tree Swallows Research Articles

Nestling Tree Swallow (Tachycineta bicolor) Diets in an Upland Old Field in Western Michigan

Abstract We collected and identified 1852 prey items from 89 boluses delivered to 62 nestling tree swallows (Tachycineta bicolor) at 14 nests in an upland old field in western Michigan. We found that 90.8% of nestling diets was insects from the Orders Diptera, Homoptera, Hymenoptera and Coleoptera. We also found clam and snail shells in boluses. Over the most common brood sizes of 4–6 nestlings, brood size was inversely proportional to the number of items per bolus delivered to nestlings although mean dry and mean organic weight of boluses did not differ. Bolus composition was not influenced by weather conditions. Nestling diets at our study site were similar in the proportions of many prey items, such as Diptera and Homoptera, to tree swallow nestling diets in other habitats but contained fewer aquatic forms such as Odonata and Ephemeroptera.

Behavioral Domination of Food Delivery by Tree Swallow Nestlings

In altricial birds, scramble competition for favorable feeding positions in the nest may cause younger chicks to starve. We studied nestling survival in a population of Tree Swallows (Tachycineta bicolor) breeding in nestboxes near Seattle, Washington, in a year of bad weather. Only a mean of 0.5 chicks fledged per nest (range 0–2, 22 nests). Nestling mortality appeared to be caused by starvation. Video filming showed that when chicks were old enough (largest chick within the brood had reached a wing length of about 55–60 mm), they spent much time in the nestbox opening, calling loudly. This behavior seemed to be driven by hunger because it occurred mainly in broods where chicks had low body masses. Parents fed the chick in the opening and did not try to push it back into the nest cavity or go around it. We suspect that blocking of the nestbox opening accelerated mortality of other young in the nest. Such behavior by dominant chicks may be more readily achieved in hole nesting birds with narrow entrances to their nest site than by open nesting birds.

Brood size and begging intensity in nestling birds

Theoretical models suggest that sibling competition should select for conspicuous begging signals. If so, begging intensity might be expected to increase with the number of competitiors. The purpose of our study was to examine the relationship between begging intensity and brood size using nestling tree swallows (Tachycineta bicolor) as our model. Over 2 years, we videotaped begging behavior in unmanipulated broods of different sizes. We found that begging intensity increased with brood size. The average weight of nestlings in each brood did not vary with brood size, but feeding rate per nestling decreased with brood size, suggesting that nestlings in larger broods begged more intensively, possibly because they were hungrier. We also conducted an experiment to examine the effect of nest mates on begging in different-sized broods. We found that nestlings with similar weights, previous competitive environments, and food deprivation begged more intensively in large broods than in small broods. Overall, our study indicates that begging intensity increases with brood size in tree swallows. This relationship may result from interactions among brood mates rather than from lower feeding rates to individual nestlings in larger broods.

Food stress, nestling growth, and fluctuating asymmetry

It has been suggested that fluctuating asymmetry (FA) is an indicator of perturbed development. Our study tests the validity of a fundamental assumption of asymmetry theory: that environmental stress imposed during development increases FA. We deprived tree swallow (Tachycineta bicolor) nestlings of food for 3 h every morning from days 3 to 15 of brood age. We obtained 2 repeated measurements of the right and left ninth primaries, outer rectrices, and tarsi, and one measure of body mass on days 8, 12, and 16. Food-deprived nestlings had significantly smaller character sizes (all characters for all days), significantly lower wing and tail feather growth rates, and significantly higher tarsal and mass growth rates than control nestlings. However, food deprivation did not cause experimental nestlings to exhibit significantly greater FA than control nestlings. Nestling mass and FA were not associated within treatments or across broods, and brood size had no significant effect upon the character size, growth rate, or FA level in nestlings. Measurement errors were small and size scaling, antisymmetry, and directional asymmetry did not confound FA estimates. Our results suggest that the ninth primaries and outer rectrices of tree swallows are unreliable indicators of FA-stress relations because of strong stabilizing selection for symmetry in this aerially insectivorous species.

Polychlorinated biphenyls and 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin equivalents in tree swallows from the upper Hudson River, New York State, USA

AbstractThe upper Hudson River of New York State, USA, is contaminated with polychlorinated biphenyls (PCBs) as a result of industrial discharges throughout the latter half of this century. In 1994 and 1995, we monitored the transfer of PCBs from aquatic sediments to a terrestrial wildlife community using the tree swallow (Tachycineta bicolor) as a model organism. Tree swallow eggs and nestlings were collected at four colonies established along a 40‐km stretch of the upper Hudson River watershed. Samples were analyzed for total PCBs and PCB congeners, including non‐ortho‐ and mono‐ortho‐substituted PCBs. Mean concentrations of PCBs in tree swallow eggs and nestlings ranged from 721 to 62,200 ng/g and were as much as 15 times greater than PCB concentrations in tree swallow eggs and nestlings collected from PCB‐contaminated areas within the Great Lakes ecosystem. The corresponding 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin equivalents (TEQs) calculated using avian toxic equivalency factors ranged from 410 to 25,400 pg/g. Concentrations of PCB congener 77 (3,39,4,49‐tetrachlorobiphenyl) were extremely elevated and were major contributors to the calculated TEQs. Homologue pattern comparisons between Hudson River and Saginaw River (Michigan, USA) ecosystems supported the hypothesis that a consistent Hudson River PCB source was the major contributor to PCBs in Hudson River tree swallows. The high concentrations of PCBs in Hudson River sediments and resultant concentrations observed in tree swallows were indicative of a potential elevated risk to these and other wildlife linked to the aquatic food web of the Hudson River ecosystem.

Microbial Colonization of the Cloacae of Nestling Tree Swallows

Microbes have the potential to be important selective forces in many aspects of avian biology. Microbes can affect fitness as a result of either their pathogenic or beneficial effects on host health. Little is known about the chronology of microbial colonization of nestlings or the effects of microbes on fledgling condition. We set out to (1) characterize the time course of microbial colonization of the cloacae of nestling Tree Swallows (Tachycineta bicolor), (2) examine the relationship between cloacal microbes and fledgling condition, and (3) determine if nest mates had similar assemblages of cloacal microbes. We repeatedly measured nestlings and sampled their cloacal microbes on nestling days 2, 3, 5, 7, 12, 16, and 19. We detected cloacal microbes in nestlings as early as nestling day 2. Colonization of nestlings by microbes began soon after hatching. Nestlings were colonized by more types of microbes and carried heavier loads of most types of microbes as they got older. Cloacal microbes did not affect fledging success. However, plate scores for gram-negative enteric lactose fermentors, which include E. coli, Salmonella spp., and Shigella spp., were positively correlated with a greater degree of wing asymmetry. This relationship suggests that microbes affect fledgling survival because wing asymmetry hinders flying ability, a critical survival skill for these aerial insectivores. Patterns in the assemblages of cloacal microbes within broods suggested host-genetic influences on the colonization of nestlings by microbes, but they also may have reflected the facts that nest mates were fed by the same adults and were raised in the same nests.

Relative importance off environmental variables in determining the growth off nestling Tree Swallows Tachycineta bicolor

Unpredictable, short‐term changes in environmental conditions associated with weather patterns have severe impacts on the reproductive success of Tree Swallows Tachycineta bicolor, as well as other aerial insectivores. We examined the effects of day‐to‐day environmental variation on the growth of nestling Tree Swallows. Using path analysis, we compared the relative importance of changes in food availability, ambient temperature and wind speed on changes in mass and feather length over four years at our study site near Ithaca, New York. Changes in environmental conditions explained a significant amount of the variation in nestling growth, with daily high temperature having the greatest influence for nestlings younger than five days. Both food supply and temperature had significant direct effects on growth of nestlings older than nine days, with temperature also having a significant indirect effect through its influence on food availability. For both young and old chicks, mass gains were smaller for chicks hatched later in the season. Environmental conditions also explained a significant amount of the linear growth of the ninth primary feather in one of two years, with food supply showing the most consistent positive effect. Environmental conditions several days prior to the measurements significantly influenced feather growth, indicating that the effects of adverse conditions are spread out over several days of feather growth, but this effect was not seen for change in mass.

Need and nestmates affect begging in tree swallows

We conducted an experiment on nestling tree swallows (Tachycineta bicolor) to examine predictions from signalling models for the evolution of conspicuous begging behaviour. Specifically, we examined the relationship between (1) nestling begging intensity and hunger, (2) begging intensity and parental provisioning and (3) begging intensity and nestmate condition. Forty broods of 9-day-old nestlings were removed from their nests for 1 h and assigned to one of the following three treatments: (1) all nestlings in the brood deprived of food (n = 13), (2) all nestlings in the brood fed (n = 11) or (3) half the nestlings in the brood deprived and half fed (n = 16). Videotapes before and after the treatments showed that begging intensity increased in broods in which all of the nestlings had been deprived and decreased in broods in which all of the nestlings had been fed. Deprived nestlings in the half-and-half treatment did not change their begging intensity in response to treatment, while fed nestlings in this treatment group showed a decrease in begging intensity. Parent tree swallows increased their feeding rate to deprived broods and decreased their rate to fed broods. Within broods, parents decreased their feeding rate to fed nestlings, but showed no significant change in feeding to deprived nestlings. Our results suggest that begging intensity is influenced by hunger and that parents appear to respond to variation in begging intensity. The begging of nestmates also appears to influence begging independently of need. These results are consistent with predictions derived from signalling models of begging.

BIOACCUMULATION OF POLYCHLORINATED BIPHENYLS FROM SEDIMENTS TO AQUATIC INSECTS AND TREE SWALLOW EGGS AND NESTLINGS IN SAGINAW BAY, MICHIGAN, USA

Sediments in the Saginaw Bay region of the Great Lakes contain concentrations and polychlorinated biphenyls (PCBs) that may adversely affect biotic species in various trophic levels. In this study the authors collected and analyzed sediments, benthic invertebrates, tree swallow eggs, and nestlings to evaluate linkages between PCBs in sediments and at various trophic levels in the Saginaw River, Michigan, USA. Their results indicate that patterns of relative concentrations of PCB congeners change with trophic level, specifically from sediment to invertebrates and from tree swallow eggs to nestlings. However, if biota-sediment accumulation factor (BSAF) values are based on only the non- and mono-ortho-substituted PCB congeners or 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEq), calculated BSAF values are close to those predicted by fugacity theory. The use of site-specific BSAF values and reference doses for toxic effects in wildlife can be used to derive sediment quality criteria (SQC) that are protective of wildlife at the top of the sediment-based food chain. The threshold concentration of TEq in sediments that would protect sensitive avian species at the same trophic level as tree swallows was calculated to be 1.5 {times} 10{sup {minus}1} TEq/g total organic carbon. Based on this value and the BSAF determined for tree swallow nestlings,more » the hazard quotient for sediments in this area was determined to be 0.7. This indicates that current concentrations of TEq due to PCB congeners in the sediments should be below the threshold for adverse effects on tree swallows. The uncertainty in the concentrations of PCB congeners in the sediments was approximately a factor of 2, which determined the degree of resolution that could be obtained from the observations made in this study.« less

Patterns of Growth and Asymmetry in Nestling Tree Swallows

Growth rates of three bilateral characters of nestling Tree Swallows Tachycineta bicolor were monitored to (a) determine the suitability of these characters in assessing fluctuating asymmetry (FA) and (b) test the hypothesis that fluctuating asymmetry of any or all of these characters is correlated with other growth parameters that may be indicative of genetic and/or environmental stress. Examination of the distribution of differences between right and left sides for tarsus, bill, and primary feather measurements reveals either directional asymmetry and/or a significant departure from a normal distribution suggesting that such characters may not be suitable for assessing fluctuating asymmetry. Further, there was little evidence that FA was correlated with any of the three growth parameters calculated from a Richards growth curve or with an overall index of growth performance for individual nestlings. Age-related trends were evident for both tarsus and primary feather asymmetry, with maximum values of asymmetry occurring during the mid or latter part of the nestling period, respectively, and declining before nestlings fledged. Such a pattern may be a normal component of growth not previously reported and related to peak growing periods for those characters.

Is there an energetic cost to begging in nestling tree swallows (Tachycineta bicolor) ?

Most honest signalling theory predicts that signals must be costly to prevent the signaller from conveying false information to the receiver. However, there have been few direct measures of the costs associated with signalling. We measured oxygen consumption during begging in 5- and 10-day-old tree swallow ( Tachycineta bicolor ) nestlings to determine if there was an energetic cost associated with this signal, and if so, whether it increased with increasing begging intensity. Our results indicated that both 5- and 10-day-old nestlings used significantly more oxygen when begging than when resting. Although both the active metabolic rate and the resting metabolic rate were significantly higher in the older nestlings than in the younger nestlings, the scope (ratio of active metabolic rate to resting metabolic rate) of begging was the same in both age groups. Our results indicated that in general begging required 28% more energy than resting in tree swallow nestlings. Energy expenditure was not related to begging intensity in 5-day-old nestlings; however, these values were significantly related in the older nestlings. Although the energetic cost of begging seems relatively low, it may be important when the total energy budget of the nestlings is considered.

Chlorinated hydrocarbons and mercury in sediments, red‐winged blackbirds (Agelaius phoeniceus) and tree swallows (Tachycineta bicolor) from wetlands in the Great Lakes–St. Lawrence River Basin

AbstractIn 1991, we collected red‐winged blackbird (Agelaius phoeniceus) eggs and tree swallow (Tachycineta bicolor) eggs and nestlings, and sediment samples from 12 wetland sites in the Great Lakes and St. Lawrence River basin. We analyzed for chlorinated hydrocarbons and total mercury and found that biota contained contaminant concentrations which were one to two orders of magnitude above those in sediments. Maximum concentrations (wet weight) of contaminants were found in Akwesasne, St. Lawrence River (PCBs = 18,558.8 ng/g in red‐winged blackbird eggs, oxychlordane = 58.8 ng/g and mirex = 40.1 ng/g in tree swallow eggs); Mud Creek, Lake Erie (total mercury = 0.079 μg/g;p,p′‐DDE = 4,376.2 ng/g in tree swallow eggs); and Cootes Paradise (211.4 ng/g dieldrin and 115.6 ng/g heptachlor epoxide in tree swallow nestlings). Despite the migratory habits of red‐winged blackbirds and tree swallows, agreement among biota and sediment in geographic variation of contaminant concentrations supports the use of these animals as biomonitors of persistent chemicals. Although chlorinated hydrocarbon concentrations in red‐winged blackbird eggs were significantly correlated with sediment contamination, the local nature of the tree swallow chick diet suggests that nestlings would be the best indicator of local contaminant trends.

Bioenergetics-Based Model for Accumulation of Polychlorinated Biphenyls by Nestling Tree Swallows, Tachycineta bicolor

A bioenergetics-based model was developed to simulate the accumulation of polychlorinated biphenyls by nestling tree swallows ( Tachycineta bicolor). The model was largely parameterized using published information for passerine birds and accurately describes the observed growth of nestling swallows. The model was evaluated by comparing predicted concentrations of selected congeners with those measured in 15 d-old nestlings collected from two sites within the Saginaw River watershed. Residue concentrations in nestlings were calculated as the sum of compound inherited in the egg and that assimilated from the diet, consisting principally of emergent aquatic insects. Model predictions were in good agreement with those measured in nestlings collected from a relatively uncontaminated site but consistently overestimated concentrations in birds from an area of known sediment contamination. The cause of this discrepancy is unknown, but did not appear to be related to metabolic biotransformation of individual congeners. Instead, it is suggested that dietary composition may have varied between sites. Alternatively, food consumption by nestling birds may have been overestimated. The results of this study indicate that caution must be used when interpreting residue information from nestling swallows, which have been proposed for use as sentinels of local sediment contamination.

Metal accumulation and metallothionein concentrations in tree swallow nestlings near acidified lakes

The authors studied metal accumulation in hepatic and renal tissues of tree swallow (Tachycineta bicolor) nestlings at acidified and nonacid reference lakes in northwestern Ontario. Hepatic concentrations of metallothionein (metal-binding proteins, MT) in tree swallow nestlings were negatively correlated with pH of the nest-site lake. Combined concentrations of Cu and Zn in the liver were correlated with liver MT concentrations, but Cd was not. Although no overt signs of metal toxicity were observed in nestlings near acid lakes, the results clearly provided evidence that metals are transferred from acid lakes to birds and that these metals are correlated with increases in hepatic MT production.

Uptake of planar polychlorinated biphenyls and 2,3,7,8-substituted polychlorinated dibenzofurans and dibenzo-p-dioxins by birds nesting in the lower fox river and Green Bay, Wisconsin, USA

The uptake of persistent polychlorinated hydrocarbons (PCHs) by four avian species was investigated at upper trophic levels of two aquatic food chains of the lower Fox River and Green Bay, Wisconsin. Accumulation of total and specific planar polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxin (PCDDs), and H411E rat hepatoma cell bioassay-derived 2,37,8-tetrachlorodibenzop-dioxin equivalents (TCDD-EQ) was evaluated in Forster's tern (Sterna forsteri) and common tern (Sterna hirundo) chicks, and in tree swallow (Tachycineta bicolor) and red-winged blackbird (Agelaius phoeniceus) nestlings from colonies nesting in several locations within the watershed. Concentrations of the PCHs were greatest in eggs and chicks of the two tern species, less in the tree swallows and least in the red-winged blackbirds. Young of all four species accumulated total PCBs, PCB congeners 77, 105, 126, and 169, and TCDD-EQ. The young birds also accumulated small concentrations of several 2,3,7,8-sbustituted PCDF and PCDD congeners. Uptake rates for certain of the PCHs for the Forster's tern chicks were: 15 μg/day for total PCBs, 70, 200, 6.5, and 0.14 ng/day for PCB congeners 77, 105, 126, and 169, respectively, and 270 μg/day for TCDD-EQ. Principal components analysis revealed that the patterns of PCH concentrations in the samples were influenced by species of bird, their age (or length of exposure) and nesting location. Collectively, our findings demonstrate that exposure of avian species to contaminants derived from aquatic food chains can be characterized and quantified for the purposes of ecological risk assessment.

Habitat Occupancy by Bachman's Sparrow in the Francis Marion National Forest before and after Hurricane Hugo

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Food availability, growth, and heritability of body size in nestling tree swallows (Tachycineta bicolor)

I studied the effects of food deprivation on the growth, final size, and inheritance of body size in nestling tree swallows (Tachycineta bicolor). Each experimental brood was divided into deprived and fed nestlings. Deprived nestlings showed relatively poor growth during the experimental stage (days 5–8), but were not significantly different in size from either their nestmates or control young at day 16. Parents of experimental broods did not compensate by increasing their food delivery rate. Heritability estimates of tarsus length were similar for deprived and fed nestlings. For control nestlings, tarsus length was significantly heritable at days 9 and 16, and bill length was heritable at day 16. There were no significant heritability estimates for wing length or body mass. Small sample sizes and single-parent–offspring regression likely inflated the standard errors associated with the heritability estimates. The mechanism that allowed deprived nestlings to grow as large as control and fed nestlings remains unknown.

Grit ingestion by nestling Tree Swallows and House Wrens

We examined the stomach contents of 200 Tree Swallow (Tachycineta bicolor) and 187 House Wren (Troglodytes aedon) nestlings for grit. Grit, composed mainly of small stones, sand, and mollusk shells or fragments, was found in 35% of the swallow and 31% of the wren stomachs. Grit ingestion started about 3 d following hatching in wrens and about 5 d after hatching in swallows. After reaching a peak, it declined in both species towards fledging. The mean number of grit particles was 10.2 in swallows and was significantly lower than that of 22.3 in wrens. The mean mass of grit particles was 17.2 mg in swallows and was significantly higher than that of 6.2 mg in wrens. The number and mass of grit particles were significantly correlated with age in swallows; only the latter correlation was significant in wrens. Analysis of a few adult stomachs suggested that grit ingestion was similar to that of nestlings.

Gamma-Radiation Effects on Nestling House Wrens: A Field Study

Freshly hatched house wren (Troglodytes aedon) nestlings were acutely exposed to γ-radiation doses of 0.9, 2.6, 4.3, and 6.0 Gy from an external source to investigate radiosensitivity in a natural setting. Observed growth statistics and parameters from the Richards model were used for growth analysis. Radiation exposure did not cause any mortality over the 15-day nestling period, but it had a depressing effect on growth in body mass and primary-feather and foot lengths. At 6.0 Gy this involved a delay in development. Effects increased in severity from 0.9 to 6.0 Gy and appeared to be linear. The 6.0-Gy nestlings were noticeably stunted. Radiation exposure did not affect the basic growth pattern. House wren nestlings responded similarly to radiation exposure as tree swallow (Tachycineta bicolor) and eastern bluebird (Sialia sialis) nestlings. There was no indication that natural variability of observed growth statistics or model parameters is correlated positively with sensitivity to radiation stress.

Growth curve analysis of birds: the Richards model and procedural problems

Four sigmoid growth curve models for birds were compared using the daily body masses and primary-feather lengths of 35 nestling tree swallows (Tachycineta bicolor). The Richards model was superior to the von Bertalanffy, Gompertz, and logistic models for body mass, but not for primary-feather length. The latter models have fixed growth forms and are special cases of the flexible Richards model. Owing to parameter correlations, the Richards model was very sensitive to the starting parameter values for the numerical computer fitting routines. The lack of data leading up to the asymptote made it difficult to calculate good starting values for primary-feather length. None of the models tested was completely satisfactory for primary-feather length, as indicated by nonrandomly distributed residuals over time. The log transformation was appropriate for body mass. It homogenized the residual variances and increased the explained percentage of variation. The explained percentage of variation was a useful selection criterion for the best-fitting model, especially since it was directly related to randomness in the distribution of the residuals and homogeneity of residual variances. However, even percentages of variation exceeding 99.5%, did not necessarily indicate an excellent fit. The Richards model did not yield more model parameters for growth curve analysis, because the shape parameter and the growth rate constant were almost perfectly correlated.