Post-breeding Period Research Articles

Reduced habitat quality increases intrinsic but not ecological costs of reproduction.

Although the costs of reproduction are predicted to vary with the quality of the breeding habitat thereby affecting population dynamics and life‐history trade‐offs, empirical evidence for this pattern remains sparse and equivocal. Costs of reproduction can operate through immediate ecological mechanisms or through delayed intrinsic mechanisms. Ignoring these separate pathways might hinder the identification of costs and the understanding of their consequences. We experimentally investigated the survival costs of reproduction for adult little owls (Athene noctua) within a gradient of habitat quality. We supplemented food to nestlings, thereby relieving the parents’ effort for brood provisioning. We used radio‐tracking and Bayesian multistate modeling based on marked recapture and dead recovery to estimate survival rates of adult little owls across the year as a function of food supplementation and habitat characteristics. Food supplementation to nestlings during the breeding season increased parental survival not only during the breeding season but also during the rest of the year. Thus, the low survival of parents of unfed broods likely represents both, strong ecological and strong intrinsic costs of reproduction. However, while immediate ecological costs occurred also in high‐quality habitats, intrinsic costs carrying over to the post‐breeding period occurred only in low‐quality habitats. Our results suggest that immediate costs resulting from ecological mechanisms such as predation, are high also in territories of high habitat quality. Long‐term costs resulting from intrinsic trade‐offs, however, are only paid in low‐quality habitats. Consequently, differential effects of habitat quality on immediate ecological and delayed intrinsic mechanisms can mask the increase of costs of reproduction in low‐quality breeding habitats. Intrinsic costs may represent an underrated mechanism of habitat quality affecting adult survival rate thereby considerably accelerating population decline in degrading habitats. This study therefore highlights the need for a long‐term perspective to fully assess the costs of reproduction and the role of habitat quality in modifying these costs.

Habitat preferences of adult Canada Jays (Perisoreus canadensis) during the post-breeding period in Algonquin Provincial Park, Ontario, Canada

Habitat preferences in animals are often examined during the breeding period when individuals are easier to observe. However, habitat use may change once young become independent and if resource availability shifts with seasonality. While Canada Jays ( Perisoreus canadensis (Linnaeus, 1766)) in Algonquin Provincial Park, Ontario, Canada, have been studied for several decades, there is no information on habitat use outside of the fall and late-winter nesting period, where they primarily used conifer forests. Using radio telemetry and resource selection functions comparing used versus available habitats, we estimated home-range size and habitat preferences of 12 adult Canada Jays ( n = 334 locations) in the spring and summer. Mean (±SD) home-range size from minimum convex polygons was 84 (±48 ha) and ranged from 35 to 201 ha. Canada Jays strongly preferred forest–wetland edges, showed a weak preference for coniferous forests, a corresponding weak avoidance of shade-tolerant hardwood forests, and used mixed forest and wetlands in proportion to their availability. Our results suggest that, while adult Canada Jays use multiple types of habitat during the post-breeding period, they also key into forest–wetland edges, likely to take advantage of emergent prey while remaining near forested areas to maximize protection from predators.

Sympatrically breeding congeneric seabirds (Stercorarius spp.) from Arctic Canada migrate to four oceans.

Polar systems of avian migration remain unpredictable. For seabirds nesting in the Nearctic, it is often difficult to predict which of the world's oceans birds will migrate to after breeding. Here, we report on three related seabird species that migrated across four oceans following sympatric breeding at a central Canadian high Arctic nesting location. Using telemetry, we tracked pomarine jaeger (Stercorarius pomarinus, n = 1) across the Arctic Ocean to the western Pacific Ocean; parasitic jaeger (S. parasiticus, n = 4) to the western Atlantic Ocean, and long‐tailed jaeger (S. longicaudus, n = 2) to the eastern Atlantic Ocean and western Indian Ocean. We also report on extensive nomadic movements over ocean during the postbreeding period (19,002 km) and over land and ocean during the prebreeding period (5578 km) by pomarine jaeger, an irruptive species whose full migrations and nomadic behavior have been a mystery. While the small sample sizes in our study limit the ability to make generalizable inferences, our results provide a key input to the knowledge of jaeger migrations. Understanding the routes and migratory divides of birds nesting in the Arctic region has implications for understanding both the glacial refugia of the past and the Anthropocene‐driven changes in the future.

Yearly Variations in GCM Concentrations in Female Mountain Hares (Lepus timidus) and the Effect of Pregnancy.

Simple SummaryThe measurement of stress hormones has become a widely used and effective tool for evaluating adrenocortical activity in animals. However, to correctly interpret stress measurements, the potential sampling bias resulting from an oversampling of individuals in different states of pregnancy has rarely been investigated. We found significant yearly variations in states of pregnancy, which is related to the conditions of the females due to the snow cover duration before and at the start of the reproductive period. These results are important for improving the interpretation of stress hormone concentrations in free-ranging populations during the breeding and reproductive periods.The measurement of glucocorticoid metabolites (GCMs) in faeces has become a widely used and effective tool for evaluating the amount of stress experienced by animals. However, the potential sampling bias resulting from an oversampling of individuals in different states of pregnancy has rarely been investigated. In this study, we validate a noninvasive method for measuring gestagen metabolites in female mountain hares (Lepus timidus) under controlled conditions. We also measured the concentration of gestagen metabolites of females in a free-ranging population during the early breeding and post-breeding periods from 2014 to 2019. We found significant yearly variations in gestagen metabolites, which were related to the condition of the females due to the snow cover duration before and at the start of the reproduction period. GCMs were significantly influenced by the gestagen metabolite levels. These results are important for improving the interpretation of GCM concentrations in free-ranging populations during the breeding and reproductive periods.

Evolution of winter molting strategies in European and North American migratory passerines.

Molt is critical for birds as it replaces damaged feathers and worn plumage, enhancing flight performance, thermoregulation, and communication. In passerines, molt generally occurs on the breeding grounds during the postbreeding period once a year. However, some species of migrant passerines that breed in the Nearctic and Western Palearctic regions have evolved different molting strategies that involve molting on the overwintering grounds. Some species forego molt on the breeding grounds and instead complete their prebasic molt on the overwintering grounds. Other species molt some or all feathers a second time (prealternate molt) during the overwintering period. Using phylogenetic analyses, we explored the potential drivers of the evolution of winter molts in Nearctic and Western Palearctic breeding passerines. Our results indicate an association between longer photoperiods and the presence of prebasic and prealternate molts on the overwintering grounds for both Nearctic and Western Palearctic species. We also found a relationship between prealternate molt and generalist and water habitats for Western Palearctic species. Finally, the complete prealternate molt in Western Palearctic passerines was linked to longer days on the overwintering grounds and longer migration distance. Longer days may favor the evolution of winter prebasic molt by increasing the time window when birds can absorb essential nutrients for molt. Alternatively, for birds undertaking a prealternate molt at the end of the overwintering period, longer days may increase exposure to feather‐degrading ultra‐violet radiation, necessitating the replacement of feathers. Our study underlines the importance of the overwintering grounds in the critical process of molt for many passerines that breed in the Nearctic and Western Palearctic regions.

Body mass dynamics of migratory nightjars are explained by individual turnover and fueling

AbstractBody mass is a commonly used indicator of the energy stores of migratory animals and there is considerable evidence that it is a critical determinant of migration decisions and outcomes. Mean population mass often increases during the post-breeding period in most migratory species. Usually, this increase is interpreted as the result of fuel accumulation for migration based on the assumption that mean population mass mirrors mean individual mass. However, an empirical test of this assumption is lacking, and it is unknown whether the general increase in mean population mass is entirely the result of within-individual mass gain, or if it rather reflects a change in the nature of individuals in the population (mass-dependent turnover). We investigated changes in body mass during the post-fledging period of a migratory bird, the Red-necked Nightjar (Caprimulgus ruficollis), and combined longitudinal and cross-sectional data collected over 9 years to disentangle the relative contribution of individual-level (mass gain) and population-level (selective appearance and disappearance) processes. We found that the average body mass of fully-developed juveniles increased as the season progressed and that both individual mass gain and the selective disappearance of lighter individuals contributed to this increase. Contrary to the general expectations for migrants, the turnover of individuals contributed 3.5 times more to the seasonal increase in average body mass than individual mass gain. On a practical note, this differential contribution implied a discrepancy of over 40% between the time-average rates of mass gain (fuel deposition rates) estimated from population-level and individual-level data. Our study calls for caution in the use of population-level changes in body mass to make inferences about individual fuel deposition rates and, more generally, indicates that longitudinal and cross-sectional approaches need to be combined to uncover phenotype-time correlations in natural populations.

Did the animal move? A cross-wavelet approach to geolocation data reveals year-round whereabouts of a resident seabird

Considerable progress in our understanding of long-distance migration has been achieved thanks to the use of small geolocator devices (GLS). The tracking of resident or short-distance migrant animals remains however challenging because geolocation errors are substantial and difficult to estimate. This study aims to examine the sex-specific marine space uses of a resident tropical seabird, the masked booby (Sula dactylatra), during its full annual life cycle at the Fernando de Noronha archipelago (Brazil). Masked boobies (n = 31) tagged with GLS recording light intensity, seawater immersion, and water temperature showed a resident behaviour over their entire annual cycle. A wavelet analysis of GLS data revealed oscillatory patterns of inferred longitude correlated with changes in immersion frequency. This synchronicity demonstrated that birds traveled away and back from the colony on consecutive trips of short length (\(\sim\) 2–4 days) and short range (\(\sim\) 100–300 km) eastward of the colony. Duration and range of trips depended on the sex of the individual and on the time of the year. Trip duration increased gradually from the end of the breeding period to the post-breeding period, probably due to the release of the central-place breeding constraints. During the pre-breeding period, females had farther ranges eastward and spent more time in water than males. Despite inherent limits of light-based geolocation, this study demonstrates the relevance of synchronicity analysis of GLS data for investigating year-round movements of resident or short-distance migrants.

Conservation and Restoration of Coastal Reed Beds in the Context of Global Change: Potential Effects of Habitat Fragmentation for Specialist Marshland Passerines

In the context of coastal marshland reduction due to sea level rise, we evaluated the value of fragmented reed beds located within agricultural polders for the conservation of habitats exploited by marshland passerines characterized by different ecological requirements. Although our study was carried out within sites sampled over different years, analyses of body condition and diet of birds during the breeding period, as well as the local daily survival rate and the body mass evolution of birds during the post-breeding period, reveal trends illustrating that fragmented reed beds within inland meadows can: (i) generate habitats that may be significantly exploited by species with a large ecological plasticity, such as the Reed Warbler that could benefit from edge effects of habitat fragmentation; (ii) offer low attractiveness for specialised species such as the Aquatic Warbler, a migratory species apparently very sensitive to the effects of reed bed fragmentation. These results underline the reed beds fragmentation effects that may impact specialised marshland passerines and which should be taken into account in wetland conservation and restoration plans.

The Role of Mountain Ranges in Shaping Population-Associated Routes of Migration: A Case Study of European Goldfinches in the Pyrenees

We aimed to describe the morphologic and isotopic differences of European Goldfinches Carduelis carduelis according to their migratory behaviour or geographic origin. We compared morphologic and isotopic variables between birds caught in two different obligatory migratory pathways (eastern and western border of the Pyrenees) and throughout the post-breeding period (from late summer to winter). The isotopic and morphological traits varied across seasons (from autumn to winter), indicating that birds captured later in the season had traits typical of longer-distance migrants that come from regions situated further north. Moreover, our results suggest that Goldfinches caught in the eastern and western borders of the Pyrenees slightly differ in body size and in one of the two colour patch-associated traits, but not in their flight apparatus or isotopic values, these last being more strongly related to their areas of origin. Such observed regional differences, therefore, may be more strongly related to other selection pressures.

First record of White-rumped Sandpiper (Calidris fuscicollis) at Esperanza/Hope Bay, Antarctica

The White-rumped Sandpiper (Calidris fuscicollis) (Vieillot 1819) is one of the longest migrating birds that breeds in the high Arctic in Alaska and Canada and spends the post-breeding period in South America. This bird is a frequent vagrant visitor of Islas Georgias del Sur/South Georgia and the South Shetland islands. Here we provide the first record for the White-rumped Sandpiper at the Continental Antarctica. The individual was observed the 2 February 2019 at Esperanza/Hope Bay (63° 23′ 56″ S, 56° 59′ 06″ W), the north of the Antarctic Peninsula, in an ice-free rockery close to a melt-water-run-off area. At the moment of the observation, the temperature was above 0 °C and the wind calm. However, strong winds from the north-west and west directions were registered during the last week of January 2019 at Esperanza Station (peak 65 knots) and at the Drake Passage (peak 49 knots) which might explain the presence of the White-rumped Sandpiper individual at Hope Bay. Our report contributes to list the non-native species observed in Antarctica. One plausible explanation could be related to changes in migratory routes of flying birds.

Consistent concentrations of critically endangered Balearic shearwaters in UK waters revealed by at-sea surveys.

AimEurope's only globally critically endangered seabird, the Balearic shearwater (Puffinus mauretanicus), is thought to have expanded its postbreeding range northwards into UK waters, though its at sea distribution there is not yet well understood. This study aims to identify environmental factors associated with the species’ presence, map the probability of presence of the species across the western English Channel and southern Celtic Sea, and estimate the number of individuals in this area.LocationThe western English Channel and southern Celtic Sea.MethodsThis study analyses strip transect data collected between 2013 and 2017 from vessel‐based surveys in the western English Channel and southern Celtic Sea during the Balearic shearwater's postbreeding period. Using environmental data collected directly and from remote sensors both Generalized Additive Models and the Random Forest machine learning model were used to determine shearwater presence at different locations. Abundance was estimated separately using a density multiplication approach.ResultsBoth models indicated that oceanographic features were better predictors of shearwater presence than fish abundance. Seafloor aspect, sea surface temperature, depth, salinity, and maximum current speed were the most important predictors. The estimated number of Balearic shearwaters in the prediction area ranged from 652 birds in 2017 to 6,904 birds in 2014.Main conclusionsAreas with consistently high probabilities of shearwater presence were identified at the Celtic Sea front. Our estimates suggest that the study area in southwest Britain supports between 2% and 23% of the global population of Balearic shearwaters. Based on the timing of the surveys (mainly in October), it is probable that most of the sighted shearwaters were immatures. This study provides the most complete understanding of Balearic shearwater distribution in UK waters available to date, information that will help inform any future conservation actions concerning this endangered species.

Diet of the lesser kestrel Falco naumanni at post-breeding roosts in southern Albania

Abstract The lesser kestrel is an insectivorous and migratory falcon species, frequently using communal roosts in the post-breeding period in southern Europe. Using pellet analysis from two post-breeding roosting sites in southern Albania collected in August 2017, we identified 1539 prey items belonging to approximately 58 prey species, 20 families and 7 orders in 110 pellets from two sites. Invertebrates made up the major part of the diet spectrum (PNI = 99.8 %, PFI = 100 %). Invertebrate prey body size varied between 8 and 62 mm (mean 28.1 mm). Bush-crickets (Tettigoniidae) and locusts (Acrididae) were the most abundant and frequent prey groups (PNI = 33 % resp. 48.6 % and PFI = 97 % resp. 94 %). Within the bush-cricket family we could identify the species of genera Tettigonia, Decticus, Platycleis, Isophya and Metrioptera. The species of genera Calliptamus, Stenobothrus and Locusta belonged among the locust species identified in the food. Birds and mammals were found in pellets only occasionally. The prey composition was rather similar at both studied sites, while locusts (Acrididae) were more abundant at the Jorgucat site and bush-crickets (Tettigonioidea) at the Mollas site in the same time. Prey groups Scarabeidae beetles and other beetles (Coleoptera other) were more abundant and frequent at Mollas than at Jorgucat, and spiders were more frequent at Jorgucat. These results suggest that the high abundance of orthopterans and beetles in the food supply in certain localities is the main reason for selection and stable occupancy of these massive communal roosting sites by lesser kestrels in Albania.

Gps Telemetry and Home Range of the White-Backed Woodpecker Dendrocopos leucotos: Results of the First Experience

The White-backed Woodpecker Dendrocopos leucotos is one the rarest and the most vulnerable woodpeckers in Europe. Intensive forest practices have caused a widespread decline of the species. In the Spanish Pyrenees, on the south-west limit of the species range, a population of the lilfordi subspecies (Lilford Woodpecker) is estimated at less than 200 individuals which are confined to a few relatively well-conserved beech forests. Despite being an endangered taxon, our knowledge about the size and shape of its home range is still incomplete. Conventional radio-tracking studies of the taxon have been limited due to the complex topography of forests, whereas miniaturized GPS devices have not been available for such a small bird (∼100 g bodyweight) until recently. Here, we evaluate for the first time the utility of modern lightweight GPS tags to characterize the home range of the White-backed Woodpecker. Using 3.4 g GPS-tags we tracked movements of 14 adult individuals during the breeding and post-breeding periods between years 2017–2019. On average, the failure rate (the percentage of failed fix attempts) was 30%, and 76% of successful fixes were accurate (error < 20 m). According to 95% kernel density estimator, the mean home range (∼300 ha) was several times larger than previously reported for the species, and it did not change over the post-breeding period. This finding challenges the utility of previous management recommendations for protecting small buffer areas around the nest or single forest stands. By modeling the home range size as a function of the number of fixes and errors, we found that males had significantly larger home ranges than females. Our results demonstrate that GPS telemetry is feasible in White-backed Woodpecker adults, and it can provide novel and accurate information about the home range of the species if potential sources of error are adequately addressed.

Effects of breeding and molt activity on songbird site fidelity

AbstractThe prebasic molt is a perilous period for songbirds, characterized by heightened energetic demands and vulnerability to predators. Given these vulnerabilities, songbirds are under selective pressure to locate and use quality habitat during the prebasic molt, potentially resulting in site fidelity between years. In this study, we aimed to determine how differences in breeding and molting activity affected site fidelity for a diversity of species at the landscape scale. To accomplish our objective, we used 31 yr of banding data from northern California and southern Oregon for 16 species of songbirds with Cormack-Jolly-Seber analyses and weighted linear regression models to assess the effects of molting and breeding activity on the probability of a species returning to a site in subsequent years. Despite substantial variation in site use for breeding and/or molting, each study species had at least some locations that were used for both breeding and molting. Captured breeding birds (n = 18,574) were much more common than molting birds (n = 7,622). Breeding activity was positively correlated with higher site fidelity for 10 of the 16 species, while we found little evidence of a relationship between molting activity and site fidelity. Only the Dark-eyed Junco (Junco hyemalis) showed increased site fidelity with increased presence of molt activity. It is likely that a shifting mosaic of food resources during the post-breeding period drives dynamic movements of songbirds in search of the necessary resources to successfully complete their annual molt.

Seasonal rainfall in subtropical montane cloud forests drives demographic fluctuations in a Green-backed Tit population

Abstract Montane birds are vulnerable to climate change. However, the mechanisms by which weather drives demographic processes in montane birds have seldom been investigated. We conducted a long-term study (2009–2019) on the Green-backed Tit (Parus monticolus), an insectivorous passerine, in the montane cloud forest of subtropical Taiwan. We explored the effects of weather variability on the productivity and survival of adult Green-backed Tits. Nest survival was negatively associated with seasonal rainfall during the breeding season (April–July) and was lower in early clutches than in late clutches. Higher typhoon-induced precipitation during the postbreeding period (July–September) was related to reduced adult survival, but neither summer temperature nor winter weather conditions were found to be related to adult bird survival. We developed a stochastic simulation model for Green-backed Tit population dynamics based on empirical data. We compared the simulated time-series and observed population growth rates (λ) and found that 80% (8/10 yr) of the observed λ fell within the 5th and 95th percentiles of the simulated data over the 10-yr period. Moreover, the simulated average (± standard deviation) of the geometric mean of λ over 10 yr (1.05 ± 0.07) was close to that observed from 2009 to 2019 (0.99), which provided confidence that the model effectively simulated the population growth rate of the Green-backed Tit. We conducted a sensitivity analysis for λ and found that juvenile and adult survival influenced by typhoon-induced rainfall were the greatest contributors to the variance in the growth rate of the Green-backed Tit population. With the onset of intensified seasonal precipitation associated with global warming, the population growth and density of Green-backed Tits will decline substantially. Our results suggest that under scenarios of high emissions of greenhouse gas, this local population of Green-backed Tits will not persist in the near future.

Effects of dietary kelp (Ascophylum nodosum) supplementation on survival rate and reproductive performance of mink challenged with Aleutian mink disease virus

Infection with Aleutian mink disease virus (AMDV) has negative effects on reproductive performance and survival rate of American mink (Neovison vison). The objectives of this study were to assess the effects of kelp (Ascophylum nodosum) supplementation on survival, growth rate, and reproductive performance of mink challenged with AMDV. AMDV-free female black mink (n = 75) were intranasally inoculated with a local AMDV strain. Mink were fed a commercial pellet supplemented with 1.5% or 0.75% kelp or were kept as controls (received no kelp) for 451 d. Body weight and rectal temperature were recorded on days 0, 31, 56, 99, 155, 366, and 451 post inoculation (PI). Annual mortality rates were 13.6%, 20.0%, and 31.8% for mink fed 1.5%, 0.75%, or 0.0% kelp, respectively (P = 0.29). Mink which were fed 1.5% kelp had a significantly (P &lt; 0.01) greater daily weight loss during breeding and post-breeding periods (days 155–366 PI), and outperformed (P &lt; 0.01) the other groups in regard to litter sizes at birth and weaning. Differences among treatments were not significant for the number of females mated, or whelped of those exposed to males, kit survival from birth to weaning, or rectal temperature. It was concluded that 1.5% kelp supplementation had beneficial effects on survival rate of adult mink and litter size.

Surveillance and habitat diversity affect European brown hare (Lepus europaeus) density in protected breeding areas

The European brown hare (Lepus europaeus) is an important game species throughout Europe. In Italy, for preventing the introduction of allochthonous strains, the management of brown hare populations has focused on the establishment of small protected areas (ZRCs), appositely managed for disposing of wild-born hares for restocking hunting territories. We investigated the effects of both land cover and surveillance on hare density and habitat preferences in 20 ZRCs, monitored twice per year (pre- and post-breeding periods) between 1997 and 2017. Density, as assessed by spotlight counts, ranged between 2.8 and 47.0 ind/km2 in spring and 5.0 and 68.4 ind/km2 in autumn. Surveillance, percent length of protected boundaries, year of institution and habitat diversity, as assessed by Shannon’s Index, were the main factors affecting hare density. During their foraging activity, hares selected ryegrass, hayfields and lucerne, while avoided maize stubble and ploughed fields and were never recorded in poplar plantations or next to human settlements. While the effects of habitat heterogeneity on hare density have been widely studied, we suggest that the involvement of local stakeholders may be of paramount importance for ensuring effective conservation measures.

Exposure of a small Arctic seabird, the little auk (Alle alle) breeding in Svalbard, to selected elements throughout the course of a year

The Arctic marine ecosystem can be altered by processes of natural and anthropogenic origin. Spatio-temporal variation in species exposure to contamination is still poorly understood. Here, we studied elemental concentrations in the non-lethally collected samples from the most numerous seabird in European Arctic, the little auk (Alle alle) nesting in one breeding colony in Svalbard. This seabird spent the breeding season in the high-Arctic zone and the non-breeding period in sub-Arctic areas what may implicate spatio-temporal variation in elements bioaccumulation. We determined concentrations of 19 elements in adults feathers to determine levels of exposure during part of the pre-breeding (n = 74) and post-breeding (n = 74) seasons, feathers from nestlings (n = 18) to determine local contamination, and chick down (n = 16) and post-hatching eggshells (n = 18) to determine maternal input to offspring. During the pre-breeding period adults accumulated in their feathers significantly more Hg (one third of feathers exceeded the established toxicity threshold), Se and Mn compared to the post-breeding period. It reflects a higher exposition of birds to contaminants in pre-breeding moult areas outside the High Arctic compared to the post-breeding moult in the High Arctic. Sex differences in adult feathers representing the post-breeding period were found only for Ca and Zn with higher values in females. Chick down was characterized by high levels of several essential elements, an intermediate level of Hg and Se, and the highest Se:Hg molar ratios of all groups. Chick body feathers had the highest level of Cu and K among all the studied groups. Post-hatching eggshells were characterized by high Sr level (exceeding 2000 μg/g). Concentrations of several non-essential elements (Bi, Cd, Cr, Hg, Ni and Pb) in them were below method detection limits.

Postbreeding Habitat Use by Golden-Cheeked Warblers (Setophaga chrysoparia)

The period following breeding but prior to migration is an important, though understudied, component of the avian annual life cycle. We quantified habitat use by endangered Golden-cheeked Warblers (Setophaga chrysoparia) during the postbreeding period in Golden-cheeked Warbler breeding habitat (i.e., oak-juniper [Quercus-Juniperus] woodlands) predominated by Texas oak (Quercus buckleyi) or post oak (Q. stellata), as well as in immediately adjacent oak woodland, oak savanna, and riparian vegetation not usually associated with breeding activity for this species. Most (87%) of the Golden-cheeked Warblers we detected were in oak-juniper woodlands, especially in Texas oak sites, but we also detected warblers in each of the other vegetation types we surveyed. Adults and family groups used breeding and nonbreeding habitat similarly, as did males and females, but juveniles used nonbreeding habitat more than adults did. Neither canopy cover nor territory density during the breeding season influenced postbreeding habitat use by warblers, regardless of vegetation type. We detected warblers 82% less often in post oak breeding habitat than in Texas oak breeding habitat despite similar densities of breeding territories, suggesting that warblers left post oak sites earlier during the postbreeding period. However, we found no evidence that warblers that bred in post oak sites were more likely to move into adjacent nonbreeding habitat than those that bred in Texas oak sites. Ashe juniper (Juniperus ashei) was the most consistently used woody substrate during the postbreeding period, regardless of warbler sex, warbler age, habitat type, or predominant oak species. Our results emphasize the continued importance of oak-juniper woodlands to Golden-cheeked Warblers during the postbreeding period but suggest that other vegetation types may also have conservation value for this species.

Effort needed to accurately estimate Vocal Activity Rate index using acoustic monitoring: A case study with a dawn-time singing passerine

Abstract Indices based on singing activity have often been used in wildlife surveys conducted with passive acoustic monitoring. For instance, the Vocal Activity Rate index (VAR) has been employed to estimate animal populations and detect changes in abundance between years or sites. VAR may differ greatly between days due to environmental and biological factors, therefore leading to inadequate population size estimations and recommendations. However, there is still little information about the minimum number of monitoring days required for estimating a reliable VAR to assess changes over time or sites. We describe, for first time for a terrestrial bird species, the pattern of variation of VAR as a function of the number of monitoring days. Coefficient of variation sharply decreased with the number of monitoring days, and this pattern was similar during the breeding and post-breeding period. Coefficient of variation was close to 100% when a single monitoring day was surveyed, but decreased up to 30% and 20% after six or seven and nine monitoring days, depending on the monitoring period. Mean VAR was significantly related to bird abundance, but no relationship was found between bird abundance and number of days needed to reach a CV lower than 20%. Our results highlight that prior assessment of effort needed to estimate a reliable VAR should be a prerequisite for future monitoring programmes using singing activity indices. We found large differences in the number of monitoring days needed to obtain a reliable VAR in comparison to prior research on seabirds, suggesting that further research should be developed in different taxa and situations.