Radio‐transmitters do not affect seasonal mass change or annual survival of wintering Bicknell's Thrushes

ABSTRACT Studies of the effects of transmitters on passerines have provided mixed results, but many have revealed no negative impacts. Most such studies have been conducted during the breeding season and, as a result, little is known about the possible effects of transmitters on wintering birds. We examined the effects of transmitters on Bicknell's Thrushes (Catharus bicknelli) wintering in the Dominican Republic. We used long‐term mark‐recapture data to compare birds with radio‐transmitters (N= 5 years, 64 individuals) to birds banded, but not radio‐tagged (N= 10 years, 164 individuals). For a subset of birds in each category, we measured the change in mass between early‐winter and late‐winter and, for all birds, we calculated return rates and modeled annual survival by sex and age classes. Return rates of radio‐tagged (16%) and banded‐only individuals (17%) did not differ, and survival models including the effect of transmitter attachment were poorly supported. We also found no sex or age‐specific effects of transmitter attachment. Radio‐tagged and banded‐only birds did not differ either in the proportion of birds gaining mass during the winter or amount of mass gained. Our results indicate that attaching light‐weight transmitters (<5% of body mass) to wintering Bicknell's Thrushes did not adversely affect either body condition or annual survival.     

Hematological stress indices reveal no effect of radio‐transmitters on wintering Hermit Thrushes

ABSTRACT Radio‐telemetry is often used to track birds, and several investigators have examined the possible effects of radio‐transmitters on birds. One approach to this question is to determine if transmitters induce physiological stress. Using hematological indicators of stress (heterophil‐lymphocyte [H/L] ratios), studies of captive birds have revealed no evidence that radio‐transmitters cause stress. However, studies in captivity may not reflect conditions faced by birds in the wild, especially during energetically demanding times, such as the overwintering period. We examined the possible effect of backpack‐style transmitters on overwintering Hermit Thrushes (Catharus guttatus) in South Carolina by examining H/L ratios from blood smears made before and after transmitter attachment. We captured and recaptured eight thrushes in an early winter period and 11 in a late winter period, and in both cases found that H/L ratios did not change after 1 mo of carrying transmitters. H/L ratios also did not differ significantly (in either trial) between thrushes with and without transmitters. Furthermore, thrushes that carried transmitters during both of our trials did not have higher final H/L ratios than those that carried transmitters during just one trial (the late winter). These results indicate that carrying backpack‐style transmitters for 1 mo did not induce stress in overwintering Hermit Thrushes. These results are consistent with studies of captive birds, and provide support for the continued use of backpack radio‐transmitters in this species, as long as weight recommendations are met.     

Variation in the extra-pair mating systems of Acadian Flycatchers and Wood Thrushes in forest fragments in southern Ontario

ABSTRACT.   The application of molecular tools to studies of avian mating systems has revealed that most songbird species engage in extra-pair matings. However, little is known about the possible effects of habitat fragmentation on extra-pair mating systems. During the breeding seasons of 2002 and 2003, we quantified the frequency of extra-pair matings in Acadian Flycatchers ( Empidonax virescens ) and Wood Thrushes ( Hylocichla mustelina ) nesting in forest fragments in southern Ontario. Acadian Flycatchers are at the limit of their northern range in southern Ontario and occurred at low densities (0.005–0.015 males/ha). Across forest fragments, 14% of young Acadian Flycatchers were the result of extra-pair fertilizations. In contrast, Wood Thrushes were common in forest fragments, with breeding densities ranging from 0.37 to 1 males/ha. Extra-pair mating was common among Wood Thrushes, with 40% of young the result of extra-pair matings. Compared to populations studied in less fragmented habitats in Pennsylvania, rates of extra-pair paternity in Ontario were lower for Acadian Flycatchers and higher for Wood Thrushes. Our results demonstrate that rates of extra-pair mating can vary across landscapes. However, the extra-pair mating systems of Acadian Flycatchers and Wood Thrushes appear to respond differently to fragmentation. We suggest that low breeding densities on fragments may be mediating the low rates of extra-pair mating observed in Acadian Flycatchers in southern Ontario, whereas changes to the behavioral tactics of male and female Wood Thrushes in southern Ontario may explain the high levels of extra-pair mating.     

Consequences of elevating plasma testosterone in females of a socially monogamous songbird: evidence of constraints on male evolution?

To explore whether selection for testosterone-mediated traits in males might be constrained by costs of higher testosterone to females, we examined the effects of experimental elevation of plasma testosterone on physiological, reproductive, and behavioral parameters in a female songbird, the dark-eyed junco (Junco hyemalis). We used subcutaneous implants to elevate testosterone (T) in captive and free-living female juncos. In captive birds, we measured the effects of high T on body mass, feather molt, and brood patch formation. In the field, we monitored its effects on the timing of egg laying, clutch size, egg size, egg steroid levels, incubation, and nest-defense behavior. Females implanted with testosterone (T-females) had significantly higher circulating levels of testosterone than did control females (C-females). Captive T-females had lower body mass, were less likely to develop brood patches, and delayed feather molt relative to C-females. Among free-living females, the interval between nest completion and appearance of the first egg was longer for T-females than for C-females and egg yolk concentrations of testosterone were higher, but there were no significant differences in estradiol levels, clutch size, or egg size. Incubation and nest defense behavior were also similar between T- and C-females. Our results suggest that selection on males for higher testosterone might initially lead to a correlated response in females producing changes in body mass and feather molt, both of which could be detrimental. Other possible female responses would be delayed onset of reproduction, which might reduce reproductive success, and higher yolk testosterone, which might have either positive or negative effects on offspring development. We found no reason to expect reduced parental behavior by females as a negative fitness consequence of selection for higher testosterone in males.     

Body condition and feather molt of a migratory shorebird during the non‐breeding season

Migratory shorebirds have some of the highest fat loads among birds, especially species which migrate long distances. The upland sandpiper Bartramia longicauda makes long‐distance migrations twice a year, but variation in body condition or timing of feather molt during the non‐breeding season has not been studied. Molt is an important part of the annual cycle of migratory birds because feather condition determines flight performance during migration, and long‐distance movements are energetically costly. However, variation in body condition during molt has been poorly studied. The objective of our field study was to examine the timing and patterns of feather molt of a long distance migratory shorebird during the non‐breeding season and test for relationships with body size, fat depots, mass, and sex. Field work was conducted at four ranches in the Northern Campos of Uruguay (Paysandú and Salto Departments). We captured and marked 62 sandpipers in a 2‐month period (Nov–Jan) during four non‐breeding seasons (2008–2012). Sex was determined by genetic analyses of blood samples taken at capture. Molt was measured in captured birds using rank scores based on published standards. Body mass and tarsus length measurements showed female‐biased sexual size dimorphism with males smaller than females. Size‐corrected body mass (body condition) showed a U‐shaped relationship with the day of the season, indicating that birds arrived at non‐breeding grounds in relatively good condition. Arriving in good body condition at non‐breeding grounds is probably important because of the energetic demands due to physiological adjustments after migration and the costs of feather molt.     

Cover,not caging,influences chronic physiological stress in a ground‐nesting bird

Predator exclosures (‘nest cages’) around nests are increasingly used to enhance hatching success of declining ground‐nesting birds. However, such exclosures are contentious and have been suggested to have detrimental effects on the species which they aim to protect. This study examines whether exclosures increase physiological stress of incubating birds, a hitherto unrecognised and untested potential drawback of exclosures. Red‐capped plover Charadrius ruficapillus hatching success was radically altered and significantly higher for nests with exclosures (96.2%) compared with those without (6.8%). Chronic physiological stress in parents (as measured by the heterophil/lymphocyte [H/L] ratio in blood) did not vary between nests with and without exclosures, or between the sexes. However the absence of vegetative cover at the nest site was associated with a 62.7% elevation in H/L ratio, indicating that incubating birds which place their nests in the open are subject to increased levels of chronic stress. The results from this study demonstrate the fundamental importance of predation for the nesting success of this species and confirm that chronic stress levels are not a detrimental side effect of exclosure use.     

Inexplicable Inefficiency of Avian Molt? Insights from an Opportunistically Breeding Arid-Zone Species,Lichenostomus penicillatus

The majority of bird species studied to date have molt schedules that are not concurrent with other energy demanding life history stages, an outcome assumed to arise from energetic trade-offs. Empirical studies reveal that molt is one of the most energetically demanding and perplexingly inefficient growth processes measured. Furthermore, small birds, which have the highest mass-specific basal metabolic rates (BMR_m), have the highest costs of molt per gram of feathers produced. However, many small passerines, including white-plumed honeyeaters (WPHE; Lichenostomus penicillatus), breed in response to resource availability at any time of year, and do so without interrupting their annual molt. We examined the energetic cost of molt in WPHE by quantifying weekly changes in minimum resting metabolic rate (RMR_min) during a natural-molt period in 7 wild-caught birds. We also measured the energetic cost of feather replacement in a second group of WPHEs that we forced to replace an additional 25% of their plumage at the start of their natural molt period. Energy expenditure during natural molt revealed an energy conversion efficiency of just 6.9% (±0.57) close to values reported for similar-sized birds from more predictable north-temperate environments. Maximum increases in RMR_min during the molt of WPHE, at 82% (±5.59) above individual pre-molt levels, were some of the highest yet reported. Yet RMR_min maxima during molt were not coincident with the peak period of feather replacement in naturally molting or plucked birds. Given the tight relationship between molt efficiency and mass-specific metabolic rate in all species studied to date, regardless of life-history pattern (Efficiency (%)  = 35.720•10^−0.494BMRm; r² = 0.944; p = <0.0001), there appears to be concomitant physiological costs entrained in the molt period that is not directly due to feather replacement. Despite these high total expenditures, the protracted molt period of WPHE significantly reduces these added costs on a daily basis.     

Costs and benefits of natal dispersal in yearling mallards Anas platyrhynchos

Costs and benefits of natal dispersal have not been fully evaluated in birds. We compared timing of breeding and nesting success for yearling female mallards Anas platyrhynchos returning to or dispersing from their natal areas. Information about natal origins was discerned with feather‐isotopes and combined with detailed reproductive histories for 503 radio‐marked females monitored at 16 study sites across the Canadian Aspen Parklands, during 1993–2000. A natal origin assignment model based on feather‐ δ³⁴S, δD, δ¹⁵N, and δ¹³C values correctly assigned 81% (112 of 138) of known‐source yearlings to region of origin; region‐specific rates ranged from 70–90%. Timing of breeding and nesting success was not related to whether or not a female had dispersed from its region of natal origin in Aspen Parkland (i.e. short‐distance dispersal) versus the southern prairies or boreal forest regions (i.e. long‐distance dispersal). Rather, nesting success was best modeled to include effects of site‐specific wetland and breeding pair abundances and an interaction between local breeding pair and wetland densities. Nest success performance relative to dispersal distance varied among study sites but was unrelated to local upland nest cover, wetland habitat conditions, or conspecific density. Thus, we detected no strong costs of dispersal but some evidence that long‐distance dispersers presumably benefitted when they were able to acquire better nest sites.     

The phenology of molting,breeding and their overlap in central Amazonian birds

The energetically challenging periods of molting and breeding are usually temporally separated in temperate birds, but can occur simultaneously in tropical birds, a condition known as molt–breeding overlap. Here, we document great variation in the timing and duration of molting and breeding, and in the extent of molt–breeding overlap, among 87 species of understory passerines in central Amazonia. We analyzed molt and breeding from 26 871 birds captured over a 30‐yr period near Manaus, Brazil. Although most species typically bred during the late dry season (about October through January), many thamnophilids apparently bred year‐round, whereas a few other species from a variety of families bred mainly during the wet season (about January through May). Of all breeding birds with an active brood patch, 12.7% were simultaneously molting. Molt–breeding overlap was more frequently observed among suboscines (13.3%), especially thamnophilids (23.0%), than oscines (6.4%). Some families had <5% molt–breeding overlap frequency, including Tyrannidae (4.4%), Tityridae (0.0%), Pipridae (1.5%), Turdidae (0.0%), and Thraupidae (0.0%), indicating that not all tropical species exhibit molt–breeding overlap. Among 31 well‐sampled species (n ≥15 brood patches), variation in molt–breeding overlap frequency was positively correlated with each species’ average duration of flight feather replacement (range 98–301 d). We also measured feather growth rates of individual birds in nine species; in five of these, slower‐growing feathers increased with an individual's probability of having molt–breeding overlap. Among furnariids, molt–breeding overlap occurred either at the beginning or end of the molt cycle, suggesting that physiological mechanisms typically separate molting from breeding. Thamnophilids showed a much different pattern; molt–breeding overlap occurred at any stage of feather replacement, apparently not regulated to be independent of breeding. These results reveal substantial life‐history variation among Amazonian birds. Future work to resolve the physiological regulation of molting and breeding in tropical birds will greatly contribute to understanding these patterns and their relevance to avian diversity.     

Use of mistletoes by the Grey Go‐away‐bird (Corythaixoides concolor,Musophagidae) in a semi‐arid savannah,south‐west Zimbabwe

Mistletoes are preferred nesting sites for many bird species in a range of habitats. However, no studies have examined the use of mistletoes by nesting birds in the semi‐arid savannah. We studied nesting in mistletoe and its role in determining nesting success in the Grey Go‐away‐bird in south‐west Zimbabwe. We modelled the effects of mistletoe, mistletoe abundance, nest microclimate, concealment and nest height on daily survival rates (DSR) using program MARK. A constant survival model was best fitted for the Grey Go‐away‐bird suggesting a constant nest survival rate across the nesting period. Mistletoe nests had lower DSR than nests placed elsewhere in the canopy. Mistletoe abundance and nest height had a positive association with DSR whereas visibility distance, microclimate and concealment were negatively associated with DSR. Overall, survival for nests in mistletoe was 22.1% compared with 90.5% for nests in other substrates over the 50‐day nesting period. In conclusion, the low nest survival in mistletoe suggests either that the factors used to select mistletoe as nest sites by these birds are poor predictors of nest success or that nesting in mistletoe may be maladaptive.     

Feather corticosterone reveals effect of moulting conditions in the autumn on subsequent reproductive output and survival in an Arctic migratory bird

For birds, unpredictable environments during the energetically stressful times of moulting and breeding are expected to have negative fitness effects. Detecting those effects however, might be difficult if individuals modulate their physiology and/or behaviours in ways to minimize short-term fitness costs. Corticosterone in feathers (CORTf) is thought to provide information on total baseline and stress-induced CORT levels at moulting and is an integrated measure of hypothalamic–pituitary–adrenal activity during the time feathers are grown. We predicted that CORTf levels in northern common eider females would relate to subsequent body condition, reproductive success and survival, in a population of eiders nesting in the eastern Canadian Arctic during a capricious period marked by annual avian cholera outbreaks. We collected CORTf data from feathers grown during previous moult in autumn and data on phenology of subsequent reproduction and survival for 242 eider females over 5 years. Using path analyses, we detected a direct relationship between CORTf and arrival date and body condition the following year. CORTf also had negative indirect relationships with both eider reproductive success and survival of eiders during an avian cholera outbreak. This indirect effect was dramatic with a reduction of approximately 30% in subsequent survival of eiders during an avian cholera outbreak when mean CORTf increased by 1 standard deviation. This study highlights the importance of events or processes occurring during moult on subsequent expression of life-history traits and relation to individual fitness, and shows that information from non-destructive sampling of individuals can track carry-over effects across seasons.     

Wintering destinations of Monterey Hermit Thrushes (Catharus guttatus slevini)

Across their broad North American distribution, Hermit Thrushes (Catharus guttatus) exhibit extensive yet subtle intraspecific variation in morphology and diverse migration patterns, causing considerable debate regarding their systematics and an incomplete understanding of their migratory geography. To better understand the fall migration and wintering destinations of Hermit Thrushes in coastal California, we deployed geolocators on individuals of the subspecies C. g. slevini breeding in the Santa Cruz Mountains of the Coast Ranges. In 2014, we captured 20 Hermit Thrushes in Big Basin Redwoods State Park using mist‐nets and attached geolocators. In 2015, we retrieved tags from 13 birds. Tagged Hermit Thrushes left the breeding area between 1 and 19 September 2014 and arrived in wintering areas in Baja California Sur and northwestern mainland Mexico between 24 September and 13 October 2014. The average distance between breeding and wintering areas was 1617 ± 217 (SD) km, and the average duration of fall migration was 22.5 ± 6.4 (SD) days. Our results suggest that Hermit Thrushes breeding in Big Basin winter in a highly concentrated region of western Mexico including Baja California Sur and southwestern Sonora or northwestern‐most Sinaloa; we found no evidence that Big Basin birds overwintered in the southwestern United States. Our results also confirm the existence of chain migration for Hermit Thrushes in California. Because C. g. slevini exhibits a limited distribution in both breeding and wintering areas and their morphology and song suggest adaptation to their habitat, we recommend exploration of fine‐scale genetic structure of coastal California’s Hermit Thrushes to determine the extent of evolutionary divergence in this subspecies.     

Coping mechanisms of alpine and arctic breeding birds: extreme weather and limitations to reproductive resilience

As ground nesting homeotherms, alpine and arctic birds mustmeet similar physiological requirements for breeding as otherbirds, but must do so in more extreme conditions. Annual springsnowfall and timing of snow melt can vary by up to 1 month anddaily temperatures near the ground surface vary from below freezingto over 45°C in alpine and arctic habitats. Species breedingin these environments have various behavioral, physiological,and morphological adaptations to cope with energetically demandingconditions. We review the ways birds cope with harsh and variableweather, and present data from long term field studies of ptarmiganto examine effects of spring weather on reproduction. In variablebut normal spring conditions, timing of breeding was not influencedby snow melt, snow depth or daily temperatures in the alpine,as breeding did not commence until conditions were generallyfavorable. Arctic ptarmigan tended to vary breeding onset inresponse to spring conditions. Generally, birds breeding inalpine and arctic habitats suffer a seasonal reproductive disadvantagecompared to birds at lower latitudes or elevations because thebreeding window is short and in late years, nest failure maybe high with little opportunity for renesting. Coping mechanismsmay only be effective below a threshold of climactic extremes.Despite strong resilience in fecundity parameters, when snowmeltis extremely delayed breeding success is greatly reduced. Alpineand arctic birds will be further challenged as they attemptto cope with anticipated increases in the frequency and severityof weather events (climate variability), as well as generalclimate warming.     

Nest positioning by male Daito White‐eyes Zosterops japonicus daitoensis improves with age to reduce nest predation risk

Age‐related improvement in reproductive success is widely observed in birds, and the mechanisms by which productivity is enhanced have received considerable attention. However, little is known about how parental age affects the loss of eggs or nestlings despite the fact that age effects on nesting success are often reported. We examined parental age effects on reproductive success in relation to the avoidance of nest predation in an island subspecies of the Japanese White‐eye, the Daito White‐eye Zosterops japonicus daitoensis. Clutch size and annual number of breeding attempts did not differ between parental age classes. Reproductive success was affected only by male age through an increase in nesting success. Nest failure was attributed only to predation in this species and nest concealment and nest height were important nest characteristics promoting successful fledging. Older males built their nests in more concealed and higher positions than first‐year birds, regardless of vegetation status around the nest. Analysis of individual birds suggested that by shifting the nest to a safer position, male White‐eyes achieved higher nesting success than in the previous year. Of three hypotheses of age‐related improvement in reproductive success considered, our data favoured the hypothesis that as individuals grow older, their breeding competence improves.     

Flexibility and constraints in the molt schedule of long‐distance migratory shorebirds: causes and consequences

Molt is a major component of the annual cycle of birds, the timing and extent of which can affect body condition, survival, and future reproductive success through carry‐over effects. The way in which molt is fitted into the annual cycle seems to be a somewhat neglected area which is both of interest and of importance. Study of the causes of annual variation in the timing of molt and its potential consequence in long‐distance migratory birds was examined using the Curlew Sandpiper, Calidris ferruginea, as a model species. Using the maximum likelihood molt models of Underhill and Zucchini (1988, Ibis 130:358–372), the relationship between annual variability in the start dates of molt at the population level with conditions on the breeding area was explored. Adult males typically started early in years when temperature in June on the Arctic breeding grounds were high compared to cold years while adult females molted later in years of high breeding success and/or warm July temperature and vice versa. When molt started later, the duration was often shorter, indicating that late completion of molt might have fitness consequences, probably jeopardizing survival. Evidence of this was seen in the low body condition of birds in years when molt was completed late. The results indicate that these migratory shorebirds follow a fine‐tuned annual life cycle, and disturbances at a certain stage can alter next biological events through carry‐over effects.     

Dexamethasone treatment supports age‐related maturation of the stress response in altricial nestling birds

In birds, the magnitude of the adrenocortical stress response can be down‐regulated during specific life‐history stages. Such modulation likely occurs when the effects of mounting robust corticosterone (Cort) elevations interfere with the normal progression of critical lifecycle activities (e.g. development, molt, migration, reproduction). The developmental hypothesis posits that altricial birds should display a ‘stress hyporesponsive period’ during the early post‐natal life stages, characterized by reduced adrenocortical stress responses compared to adult birds and a gradual age‐related increase. Such modulation would allow avoiding the potential deleterious effects that long‐term elevations of circulating Cort might exert on growth and development, when the physiological and behavioral abilities to cope with disturbance are limited. Two proximate hypotheses have been proposed to explain this age‐dependent pattern of Cort secretion. The ‘maturation hypothesis’ proposes a progressive age‐related growth, maturation and enhanced sensitivity to sensory input of the Hypothalamic‐Pituitary‐Adrenal (HPA) axis tissues, whereas the ‘negative feedback attenuation hypothesis’ proposes a gradual attenuation in the intensity of the negative feedback in the HPA axis. Here we tested these hypotheses by experimentally inducing negative feedback on the HPA axis via dexamethasone (DEX) treatment in nestling white storks Ciconia ciconia. Nestling age positively affected stress‐induced plasma Cort (STRESS‐Cort) levels during experimental handling and restraint, thus supporting the developmental hypothesis. DEX treatment significantly reduced STRESS‐Cort levels compared to saline (SAL) treatment, thus eliciting the expected negative feedback on the HPA axis. However, inter‐ and intra‐individual comparisons indicated no age effects on the intensity of the negative feedback exerted by DEX. Our results do not support the negative feedback attenuation hypothesis and suggest that progressive maturation of the HPA axis tissues is the proximate mechanism responsible for age‐related changes in the stress response during avian post‐natal development. We encourage further tests of the proposed proximate mechanisms during migration, breeding and molt.     

A pre‐breeding immune challenge delays reproduction in the female dark‐eyed junco Junco hyemalis

Precise timing of life‐history transitions in predictably changing environments is hypothesized to aid in individual survival and reproductive success, by appropriately matching an animal's physiology and behavior with prevailing environmental conditions. Therefore, it is imperative for individuals to time energetically costly life‐history stages (i.e. reproduction) so they overlap with seasonal peaks in food abundance and quality. Female lifetime reproductive fitness is affected by several factors that influence energy balance, including arrival date, timing of egg production, and energetic condition. Therefore, any extra energetic costs during reproduction may negatively affect timing of egg production, and ultimately a female's fitness. For example, mounting an immunological response elicits a high energetic cost, and this transfer of resources towards cell and immune system maintenance could have direct negative effects on reproductive timing. In order to determine whether an immune challenge delays onset of breeding (i.e. egg production), we administered either a humoral immune challenge (keyhole limpet hemocyanin (KLH)) (treatment) or physiological saline (control) to free‐living female dark‐eyed juncos Junco hyemalis in the period immediately prior to egg‐laying (～4 weeks). We found that KLH‐injected females artificially delayed clutch initiation when compared to control females. These data help to refine our understanding of how free‐living birds allocate resources between reproduction and self‐maintenance processes during the critical pre‐laying period of the annual cycle.     

The trade-off between molt and parental care: a sexual conflict in the blue tit?

Breeding activities and molt are generally thought to be mutuallyexclusive in birds since both are energetically costly and arenormally separated in time. However, sometimes molt overlapswith breeding to some degree. A trade-off between adult somaticmaintenance functions (feather renewal) and parental care isthen to be expected. The consequences of this are largely unknown,and there are few studies that have shown any fitness costsof molt-breeding overlap. We investigated the consequences ofmolt-breeding overlap by removing first clutches of blue titParus casruleus pairs, thereby inducing late repeat clutches.Among the delayed pairs, a high proportion of males and somefemales started their molt already during incubation or nestlingfeeding. Molting males fed their nestlings to a lesser extentthan non-molting ones, and nestling mortality increased as adirect result of the early timing of male molt. Furthermore,the ability to raise an experimentally enlarged brood was negativelycoupled to the molt stage of the male. Our data thus provideevidence that molt-breeding overlap leads to fitness costs,and we discuss the results within the context of sexual conflictand the implications for optimization of avian reproductivedecisions     

Long-Term Effects of Chronic Light Pollution on Seasonal Functions of European Blackbirds (Turdus merula)

Light pollution is known to affect important biological functions of wild animals, including daily and annual cycles. However, knowledge about long-term effects of chronic exposure to artificial light at night is still very limited. Here we present data on reproductive physiology, molt and locomotor activity during two-year cycles of European blackbirds (Turdus merula) exposed to either dark nights or 0.3 lux at night. As expected, control birds kept under dark nights exhibited two regular testicular and testosterone cycles during the two-year experiment. Control urban birds developed testes faster than their control rural conspecifics. Conversely, while in the first year blackbirds exposed to light at night showed a normal but earlier gonadal cycle compared to control birds, during the second year the reproductive system did not develop at all: both testicular size and testosterone concentration were at baseline levels in all birds. In addition, molt sequence in light-treated birds was more irregular than in control birds in both years. Analysis of locomotor activity showed that birds were still synchronized to the underlying light-dark cycle. We suggest that the lack of reproductive activity and irregular molt progression were possibly the results of i) birds being stuck in a photorefractory state and/or ii) chronic stress. Our data show that chronic low intensities of light at night can dramatically affect the reproductive system. Future studies are needed in order to investigate if and how urban animals avoid such negative impact and to elucidate the physiological mechanisms behind these profound long-term effects of artificial light at night. Finally we call for collaboration between scientists and policy makers to limit the impact of light pollution on animals and ecosystems.     

Anti-parasite treatment removes negative effects of environmental pollutants on reproduction in an Arctic seabird

Recent studies have shown that the detrimental effects of anthropogenic pollutants may be worse if organisms are exposed to natural stress. In this study, we examined whether negative effects of organochlorines (OCs) could be influenced by parasites. In two breeding seasons, we administered an anti-helminthic drug to groups of breeding glaucous gulls (Larus hyperboreus), whereas control groups were placebo treated. In all birds, blood residues of the most important OCs in the study population (hexachlorobenzene, oxychlordane, p,p'-dichlorodiphenyldichloroethylene and polychlorinated biphenyl), were measured. The relationships between OCs and fitness components (i.e. nesting success and return rate between breeding seasons) were then compared between the birds receiving anti-parasite treatment and the controls. Among untreated males, higher blood residues of OCs were associated with lowered nesting success, while in males receiving anti-parasite treatment, there was no detrimental effect of OCs on fitness. Return rate was not affected by treatment or OCs. Our findings suggest that parasites may be an important factor in triggering reproductive effects of such pollutants, and that relatively low levels of OCs may have serious reproductive consequences in natural populations when stress from other sources is high.