Hatch Date Research Articles

Hydrologic Correlates of Reproductive Success in the Alligator Gar

AbstractPrevious work relating adult age data to historic hydrology indicated that strong year‐classes of Alligator Gar Atractosteus spatula were rare, tied to major flooding events, and linked to the inundation and connectivity of floodplain habitats. Although spawning habitat suitability criteria have been correlated with successful recruitment in Texas Alligator Gar populations, direct evaluation of recruitment documenting young‐of‐the‐year (age‐0) presence or abundance has not been reported. To specify conditions associated with successful spawning and recruitment of Alligator Gar, we sampled for age‐0 fish monthly from May to July 2013–2017 in the Trinity River and from May to July 2015–2017 in Choke Canyon Reservoir. Suitability criteria predicted strong year‐classes in 2015 and 2016 for the Trinity River and in 2015 for Choke Canyon Reservoir; the predictions were confirmed by the presence of abundant age‐0 Alligator Gar in those systems and years. Hatch dates of juvenile Alligator Gar were estimated from otoliths and compared to corresponding environmental and hydrologic conditions. Hatch date analyses indicated a protracted spawning duration in 2015 associated with extended widespread flooding and a narrower range of spawning dates in 2016. Due to rapid growth and variable gear efficacy relative to fish size, multiple gears were required to assess the full size range of age‐0 Alligator Gar. A standardized sampling framework that included visual searching and floating mini‐fyke nets effectively sampled age‐0 Alligator Gar from 15 to 650 mm TL. We recommend a two‐tiered approach for predicting and monitoring Alligator Gar recruitment. First, the monitoring of hydrology and the application of suitability criteria can provide an early predictor of potential Alligator Gar reproductive success. If conditions are favorable for spawning, then sampling for age‐0 Alligator Gar can confirm recruitment and can give an indication of the spatial extent (visual searching) and relative abundance (visual searching and/or mini‐fyke nets) of successful reproduction.

Otoliths Reveal Spawning Ecology and Early Life History of Sympatric Catostomids

AbstractDifferences in spawning ecology and early life history may influence the recruitment success of three sympatric catostomids in the Colorado River basin: the Bluehead Sucker Catostomus discobolus, Flannelmouth Sucker C. latipinnis, and federally endangered Razorback Sucker Xyrauchen texanus. In the San Juan River, all three species annually produce larvae, but only Bluehead and Flannelmouth suckers regularly recruit to the juvenile phase and older. Otolith microstructure analysis can determine age, growth rates, and spawning periodicity and may elucidate possible reasons for differences in recruitment among species. Larval suckers were collected from low‐velocity habitats in the San Juan River in 2011; fish were measured, and ontogenetic phase and fish age were determined from otolith increment counts. Otolith age was used to determine hatch dates and spawning periodicity, calculate daily growth rates, and develop three candidate growth functions relating fish age and body length. Relative to Bluehead and Flannelmouth suckers, Razorback Suckers had a shorter spawning period, lower growth rate, and a higher proportion of the least developed ontogenetic phase. The small size of Razorback Suckers relative to other suckers may result in higher predation and lower prey acquisition, thus restricting their transition to more developed phases and limiting recruitment to the juvenile phase. Model ranking based on Akaike's information criterion (corrected for small sample size) was nearly identical for all growth functions. The early life history information we provide may guide flow releases in this regulated system to provide suitable backwater habitat and warmer water temperatures compatible with reproduction, growth, and survival of native catostomids, including the endangered Razorback Sucker. However, due to the limited temporal and geographic extent of samples used in this study, data presented herein are not inclusive of all conditions under which suckers may be present in the San Juan River.

Seasonal Abundance and Nutritional Concentration of Grassland Arthropods

A comprehensive understanding of foraging choices within an optimal framework requires a basic understanding of the differential nutritive concentrations and availability of prey items. Herein we present both nutritional data (e.g., the macronutrient, gross energy, and mineral concentrations) and temporal abundance of wild-caught arthropods from Nebraska prairies. Additionally, we report the size-mediated nutritional concentrations of 2 Orthoptera families: Acrididae and Tettigoniidae. Crude fat concentrations were 56%, 63%, and 53% higher in small, medium, and large Tettigoniidae than in Acrididae, respectively. Crude protein concentration varied minimally among arthropod groups (range 60.32%–76.00%), while caloric densities (gross energy) were similar among the majority of arthropod groups that were analyzed (range 16.54–23.36 kJ/g). In addition, small (early instar) orthropterans peaked synchronous to the mean first clutch hatch date for 2 species of grassland birds at the study site. Our results suggest that size and insect taxonomy influence crude fat and protein concentrations but do not appear to influence gross energy concentrations. Peak fat and protein concentration occurred during the early nestling phase for both avian species, implying synchrony between food availability and the nestling provisioning period for grassland nesting birds.

Age determination for juvenile fourfinger threadfin (Eleutheronema rhadinum) by using otolith microstructure and length data obtained from commercial fisheries off northwestern Taiwan

The fourfinger threadfin (Eleutheronema rhadinum) is a commercially crucial species for coastal and inshore small-scale fisheries, but is rarely studied to understand its life history, including age and growth. The present study examined the daily growth increment in otoliths for the species during its early life stages by using otolith microstructure analysis, and corroborated the age estimates using alternative information and approaches. The daily growth increments were discovered to be formed and spaced regularly. The fish samples were successfully aged at between 174 and 652 days, with the growth rate fairly consistent among individuals. The mean length at age 1 year of E. rhadinum was estimated at 29.7 cm fork length using the fitted growth equation. Hatch dates, estimated using the daily increments and the date of capture, were mostly from April to August. We further corroborated the age estimates by using identifiable modes of younger fish in the monthly length–frequency samples. The lengths-at-age, predicted using the growth equation with best fit, were discovered to correspond favorably with the progress of the modes in the length–frequency distribution of sampled landed fish. A framework that incorporates information available from alternative approaches to determine and corroborate estimates of fish age can be developed, as demonstrated in this study.

Local recruitment in Northern Flickers is related to environmental factors at multiple scales and provides reproductive benefits to yearling breeders settling close to home

Abstract Natal dispersal and local recruitment are affected by factors both intrinsic and extrinsic to juveniles and may affect fitness. Understanding the relationship between dispersal and population density in birds has been hindered by a lack of long-term studies and a focus on resident species has neglected the role of weather operating at large spatial scales. I studied local recruitment and the reproductive consequences of natal dispersal distance within a population of Northern Flickers (Colaptes auratus), a migratory woodpecker. During a field study spanning 16 yr in British Columbia, 8,272 fledglings were banded and 138 males and 105 females recruited locally. The average annual local recruitment rate for males (3.36%) was greater than that for females (2.55%) and the propensity to recruit locally was positively correlated with an early hatch date and high body condition. Annual local recruitment was not associated with population density in the year of hatch but was positively correlated with population density in the year of settlement. Local recruitment was also positively correlated with warmer springs during migration, consistent with the phenology hypothesis that the location of settlement is affected by weather along the route. Among local recruits, natal dispersal distance was independent of the presence of parents and so dispersal was not a behavior to prevent inbreeding. However, settling closer to the natal site led to reproductive benefits in terms of earlier laying dates and better nest success. Therefore, juveniles may gain useful information about the location of nesting substrates, predation risk, and patchy food resources by exploring the landscape around their natal site during the post-fledging period and then settling in the familiar area after returning from migration.

Lead concentrations in blood from incubating common eiders (Somateria mollissima) in the Baltic Sea

Here we investigate if lead may be a contributing factor to the observed population decline in a Baltic colony of incubating eiders (Somateria mollissima). Body mass and blood samples were obtained from 50 incubating female eiders at the Baltic breeding colony on Christiansø during spring 2017 (n = 27) and 2018 (n = 23). All the females were sampled twice during early (day 4) and late (day 24) incubation. The full blood was analysed for lead to investigate if the concentrations exceeded toxic thresholds or changed over the incubation period due to remobilisation from bones and liver tissue. Body mass, hatch date and number of chicks were also analysed with respect to lead concentrations. The body mass (mean ± SD g) increased significantly in the order: day 24 in 2018 (1561 ± 154 g) < day 24 in 2017 (1618 ± 156 g) < day 4 in 2018 (2183 ± 140 g) < day 4 in 2017 (2359 ± 167 g) (all p < 0.001). The lead concentrations increased significantly in the opposite order i.e. day 4 in 2017 (41.7 ± 67.1 μg/L) < day 24 in 2017 (55.4 ± 66.8 μg/L) < day 4 in 2018 (177 ± 196 μg/L) < day 24 in 2018 (258 ± 243) (all p < 0.001). From day 4 to 24, the eider females had a 1.33-fold increase in blood lead concentrations in 2017 and a 1.46-fold increase in 2018. Three of the birds (13%) sampled in 2018 had lead concentrations that exceeded concentrations of clinical poisoning (500 μg/L) and eleven (48%) had concentrations that exceeded the threshold for subclinical poisoning (200 μg/L). In 2017, none of the birds exceeded the high toxic threshold of clinical poisoning while only one (4%) exceeded the lower threshold for subclinical poisoning. Three of the birds (6%) sampled in 2018 had lead concentrations that exceeded those of clinical poisoning while 12 birds (24%) resampled in both years exceeded the threshold for subclinical poisoning. In addition, lead concentrations and body mass on day 4 affected hatch date positively in 2018 (both p < 0.03) but not in 2017. These results show that bioavailable lead in bone and liver tissue pose a threat to the health of about 25% of the incubating eiders sampled. This is particularly critical because eiders are largely capital breeding which means that incubating eiders are in an energetically stressed state. The origin of lead in incubating eiders in the Christiansø colony is unknown and it remains an urgent priority to establish the source, prevalence and mechanism for uptake. The increase in lead from day 4 to day 24 is due to bone and liver remobilization; however, the additional lead source(s) on the breeding grounds needs to be identified. Continued investigations should determine the origin, uptake mechanisms and degree of exposure to lead for individual birds. Such research should include necropsies, x-ray, lead isotope and stable C and N isotope analyses to find the lead sources(s) in the course of the annual cycle and how it may affect the population dynamics of the Christiansø colony which reflects the ecology of the Baltic eiders being suitable for biomonitoring the overall flyway.

Consequences of differences among readers in age estimations of Baltic cod larvae and early juveniles for growth rate and hatch date analysis. Is more experience always better?

We evaluated the precision (i.e., reproducibility of estimations) and accuracy (i.e., reflection of true age) of ageing larval and early juvenile Baltic cod, Gadus morhua, (4.1–33 mm SL) from sagittae and lapilli by inexperienced and experienced readers and an expert. For all three readers, lapilli provided higher precision and accuracy of age estimates than did sagittae. Moreover, with the used method of unpolished otoliths analysis, lapilli allowed ageing juveniles larger (up to 33 mm SL) than did sagittae (up to approximately 18 mm SL). With regard to the level of experience of the reader ageing larval fish, the highest precision in ageing was achieved by the expert and experienced reader, and the lowest by the inexperienced reader. Interestingly, reader experience was not reflected in the accuracy of estimates as it was higher with the inexperienced reader than with the experienced one. Differences in ageing among readers had significant consequences for growth rate analysis (slope of regression line fitted to SL-at-age data). The results obtained covered a wide range of values, from 0.11 mm day−1 to 0.45 mm day−1 for sagittae and from 0.21 mm day−1 to 0.68 mm day−1 for lapilli. The consequences of ageing error for back-calculated hatching dates were statistically significant as well. It may be therefore recommended to use lapilli for cod larvae and early juveniles ageing. Moreover, it is recommended not to make a quick assumption that ageing done by more experienced reader must provide more accurate results that better reflect true age, even if precision of the increment counts is for the more experienced reader high.

Shifts in hatching date of American crocodile (Crocodylus acutus) in southern Florida.

Globally temperature of marine environments is on the rise and temperature plays an important role in the life-history of reptiles. In this study, we examined the relationship between sea surface temperature and average date of hatching for American crocodiles (Crocodylus acutus) over a 37-year period at two nesting sites, Everglades National Park and Florida Power and Light Turkey Point Power Plant site in southern Florida. Our results indicate that hatch dates are shifting 1.5 days earlier every two years and at half that rate for the Turkey Point site, and with every 1°C degree increase in temperature, hatching occurs about 10 days earlier in the Everglades and 6 days earlier at Turkey Point. Our results on shifting hatch dates for American crocodiles provide further details about the impacts of temperature change on crocodile life history and suggest that increased temperature may affect their phenology.

Distribution, age and growth of the diamondback squid, Thysanoteuthis rhombus (Cephalopoda: Thysanoteuthidae) from the tropical Arabian Sea

Individuals in all life stages of the large oceanic diamondback squid Thysanoteuthis rhombus were observed in the southeastern Arabian Sea. A total of 82 individuals were collected from the Arabian Sea between February 2013 and December 2018. The length-weight relationship follows an allometric growth pattern. Age and growth were estimated by statolith increment analysis (n = 77) and demonstrated a rapid growth rate ranging from 1.42 to 4.80 mm dorsal mantle length (DML)/day. Based on back calculated hatch dates, T. rhombus spawned from May to December with a peak in July. Male and female squids matured at 6 months of age. The oldest individual was a mature female (655 mm DML) that was 220 days old with a growth rate of 2.97 mm DML/day. Differences in size-wise (DML) instantaneous growth rates were evident. Stomach content analysis revealed that fish and squid were the major prey of adults and sub-adults, while in juveniles, crustaceans were the dominant prey item. Ontogenetic differences in the diet were apparent.

A multiscale assessment of Red-tailed Hawk reproductive success relative to urban density and habitat type

AbstractDespite the unique threats to wildlife in urban areas, many raptors have established successfully reproducing urban populations. To identify variations in raptor breeding ecology within an urban area, we compared metrics of Red-tailed Hawk reproductive attempts to landscape characteristics in Reno and Sparks, NV, USA during the 2015 and 2016 breeding seasons. We used the Apparent Nesting Success and logistic exposure methods to measure nesting success of the Red-tailed Hawks. We used generalized linear models to relate nesting success and fledge rate to habitat type, productivity to hatch date (Julian day) and hatch date to urban density. Nesting success was 86% and 83% for the respective years. Nesting success increased in grassland-agricultural and shrub habitats and decreased in riparian habitat within the urban landscape. Productivity was 2.23 and 2.03 per nest for the breeding seasons. Fledge rates were 72% and 77%, respectively, and decreased in riparian areas. Nestlings hatched earlier with increased urban density and earliest in suburban areas, following a negative quadratic curve. Nesting success and productivity for this population were high relative to others in North America. Productivity increased in habitats where ground prey was more accessible. We suggest that suburban areas, if not frequently disturbed, provide sufficient resources to sustain Red-tailed Hawks over extended periods. As urban expansion continues in arid environments globally, we stress that researchers monitor reproductive output across the urban predator guild to elucidate patterns in population dynamics and adaptation.

Sub-annual cohort representation among young-of-the-year recruits of the western stock of Atlantic bluefin tuna

The western stock of Atlantic bluefin tuna receives recruits principally from spawning habitats in the Gulf of Mexico although the recent discovery of bluefin tuna larvae in the western North Atlantic Slope Sea calls into question whether there is another key source of recruits to the western stock. We tested whether age-0 juveniles occurring in the US Mid-Atlantic Bight during the late summer might originate from Slope Sea spawning by estimating the hatch date distribution based on otolith microstructural analysis given larval production occurs approximately two months later in the Slope Sea (late June to early August) than in the Gulf of Mexico (early April to mid-June). Following a review of the literature on ageing methodology for Thunnini species, we attempted trials on both sectioned and whole un-sectioned otoliths, and adopted the latter based on higher precision levels. Estimated ages ranged from 122 to 175 (days post hatch) for fish ranging 23.2–36.3 cm fork length. Hatch dates ranged 20 March to 12 May 2010, exhibiting a unimodal distribution. Hatch dates mainly occurred in early-April 2010, which corresponded to the spawning and larval production period for the Gulf of Mexico. Estimated growth rate (size-at-age) was 1.1 mm d−1. Thus, we failed to observe evidence for recruitment from the newfound Slope Sea spawning region, albeit our sample represents only a single year and region. More conclusive inferences on recruitment from the Slope Sea spawning will depend on a greater sample of age-0 juveniles sampled across years or molecular approaches that can identify recruits in older juveniles and adults.

Short-term variations in the early life history traits of common sardine Strangomera bentincki and anchoveta Engraulis ringens off central Chile

A comparison of the early life history traits of two small pelagic fish species occurring in nearshore waters of central Chile was carried out based on the analysis of sagittal otolith microstructure. Plankton samples were collected in a shallow embayment at weekly scale, during six nights of austral spring 2015. Mixed schools of larval common sardine Strangomera benticki and anchoveta Engraulis ringens were studied, where the former was two to three-times more abundant than the latter. Anchoveta larvae grew faster (0.738 mm day−1) than larval sardine (0.639 mm day−1) but hatched at smaller size (2.62 vs. 4.85 mm, respectively); larval mortality rates was higher for sardines than anchovetas (ZSb = -0.164 day−1; ZEr = -0.136 day−1). Back-calculated hatch dates indicate that both species were temporally coupled, excepting during early November 2015, when a large hatch event of anchoveta occurred. Both species showed similar growth trajectories during early ontogeny; however, the residuals of the micro-increment width in sagittal otoliths were negatively correlated between species. A regional warming event (SST > 15 °C) of coastal waters during late October 2015, negatively affected the recent growth rates of larval anchoveta, but not for sardines. Therefore, during spring, larvae of small epipelagic species display different responses to the same environmental forcing in the nearshore.

Riding the storm out: select demographics of a breeding population of Cooper’s hawks (Accipiter cooperii) following a severe spring snowstorm

Abstract The demographic responses to severe weather by top-level predators, including birds of prey, are underreported and/or unknown. Severe storms are predicted by climate change models to increase globally and in frequency into the 22nd century. In April 2018, a population of breeding Cooper’s hawks (Accipiter cooperii) in central Wisconsin, USA, experienced three days of heavy snowfall in the most severe storm, in pre-incubation-stage, for 39 years (1980–2018). Here I report select demographic outcomes of this nesting population following this intense weather. The median hatching date of 10 June in 2018 was the sixth latest such metric in those 39 years (and the latest in 22 years since 1996) for this population, which has advanced its breeding schedule about 1.3 days/decade due to climate change or warming. Survival of a total of 16 color-marked breeding adults, 15 males and 1 female, observed pre-storm in the nesting areas, was 100% up through the late nestling stage in the same nesting areas where these birds were initially detected in 2018. Average clutch size (4.4 eggs/nest) and average brood size (4.0 young/nest) were similar to the overall average annual metrics of these demographics for this population in the earlier 38 study years. Nest success, whereby 95% of 21 nests with eggs produced advanced-aged young, was higher in 2018 than the overall average of 77% nest success rate during the earlier years. The later timing of hatching in 2018, likely due to the severe spring snowstorm, appeared to have no deleterious effects either on survival of the breeding adults or on the reproductive output of this healthy study population. Tree-canopy prey may have served as important alternative food for this typically ground-foraging raptor in 2018.

Discriminating Natal Source Populations of a Temperate Marine Fish Using Larval Otolith Chemistry

The life cycles of many marine species depend on a dispersive larval stage that connects spatially segregated populations. However, quantifying larval movement among populations remains one of the greatest challenges in marine ecology. Such movement determines whether a population is essentially a self-recruiting stock, or if it forms part of a larger meta-population where recruits originate from multiple sources. Previous research has struggled to differentiate between such stock structure models for King George whiting (Sillaginodes punctatus; Perciformes) in southern Australia, largely due to difficulties in identifying the source populations of dispersing larvae. In this study, pelagic larvae were collected throughout the only recognized spawning area in South Australia in 2017 and 2018. First, we identified that the distribution of larvae was broadly divisible into two groups – those in southern Spencer Gulf and those in Investigator Strait. Then, the incremental structure and elemental composition of otoliths of larvae from the two regions were compared to determine if they had originated from a common source population. There were no spatial differences in the sizes (3.0-5.0 mm SL), ages (5-21 d), hatch dates (7-24 April) or average growth rates (0.09-0.21 mm d-1) of larvae. However, multi-elemental (Li, Mg, Mn, Sr and Ba) otolith signatures differed significantly between the two regions, primarily driven by differences in concentrations of Li and Ba. Although otolith signatures were year-specific, larvae were assigned to their region of capture with 70-82% accuracy. Larvae in each region hatched at the same time yet had significantly different otolith chemistry, providing strong evidence that those in southern Spencer Gulf and Investigator Strait originated from spatially segregated water masses. This study has demonstrated the ability of otolith chemistry to discriminate source populations of pelagic larvae in a fully marine environment, which provides a basis to quantify larval movement between fish populations.

Age and growth of stocked juvenile Shoal Bass in a tailwater: Environmental variation and accuracy of daily age estimates.

Otolith microanalysis is often used to assess population age structure and growth of fishes during their early stages. Shoal Bass Micropterus cataractae is a recently described species of conservation concern and little is known regarding factors affecting their recruitment. In 2004, Georgia Department of Natural Resources (GADNR) and the US National Park Service (NPS) stocked Shoal Bass marked with oxytetracycline (OTC) in the Chattahoochee River near Atlanta, Georgia in an effort to restore this population, creating known-age fish to examine the effect of environment on daily age accuracy. We obtained samples of stocked juvenile (<150 mm) Shoal Bass from standard monitoring that occurred approximately 30–60 days after stocking in the Chattahoochee River to 1) validate daily rings for estimating age, hatch dates, and growth rates for stocked age-0 Shoal Bass, and 2) evaluate the effect of habitat (location) on age bias. Shoal Bass otoliths were examined for OTC marks and daily rings were counted in reference to OTC marks to assess age estimation accuracy. Age estimation accuracy ranged from -2 to -25 days and was influenced by the environment where Shoal Bass were captured, with greater inaccuracy in colder water temperatures. Fish collected from locations with colder temperatures displayed closer spacing of daily rings, potentially leading to greater underestimation of age. Growth rates of stocked Shoal Bass, corrected for age estimation error, ranged from 0.5 mm/day to 0.8 mm/day. This study demonstrates the effect of environmental variability on age inaccuracy and subsequent interpretation of results. Incorporating methods to assess age estimation accuracy is needed to understand interspecific differences in recruitment among black bass species in the variety of natural and human-modified environments they inhabit.

Estimating Montezuma quail hatch date using primary molt at harvest

ABSTRACTThe Montezuma quail (Cyrtonyx montezumae) is an arid‐land quail species found locally in the southwestern United States, and south into Mexico following the Sierra Madre Occidental mountain range to Oaxaca. The reproductive season (Jun to Sep) for Montezuma quail is late compared with other quail species, excluding scaled quail (Callipepla squamata). We used plumage characteristics to age hunter‐harvested wings (harvested 2008–2009 in Pima and Santa Cruz counties, AZ, USA) and back‐dating methods based on primary‐feather molt to estimate hatch date. We found peak hatch occurred from late July to mid‐August, with 10.6% of estimated hatch dates in October, which is later than previously reported. Future research should focus on determining how annual precipitation influences hatch date using hunter‐harvested wings and back‐dating techniques. © 2019 The Wildlife Society.

Direct and indirect effects of regional and local climatic factors on trophic interactions in the Arctic tundra

Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge. Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator-prey interactions of species sharing a tundra food web. We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey - lemmings (preferred prey) and snow geese (alternate prey) - which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long-term dataset (21years). We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance. Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator-prey interactions and our capacity to anticipate food web response to ongoing climate change.

Long-term phenology of two North American secondary cavity-nesters in response to changing climate conditions

Wildlife populations can respond to changes in climate conditions by either adapting or moving to areas with preferred climate regimes. We studied nesting responses of two bird species, western bluebird (Sialia mexicana) and ash-throated flycatcher (Myiarchus cinerascens), to changing climate conditions (i.e., rising temperatures and increased drought stress) over 21 years in northern New Mexico. We used data from 1649 nests to assess whether the two species responded to changing climate conditions through phenological shifts in breeding time or shifts in nesting elevation. We also examined changes in reproductive output (i.e., clutch size). Our data show that western bluebirds significantly increased nesting elevation over a 19-year period by approximately 5 m per year. Mean spring temperature was the best predictor of western bluebird nesting elevation. Higher nesting elevations were not correlated with hatch dates or clutch sizes in western bluebirds, suggesting that nesting at higher elevations does not affect breeding time or reproductive output. We did not observe significant changes in nesting elevation or breeding dates in ash-throated flycatchers. Nesting higher in elevation may allow western bluebirds to cope with the increased temperatures and droughts. However, this climate niche conservatism may pose a risk for the conservation of the species if climate change and habitat loss continue to occur. The lack of significant changes detected in nesting elevation, breeding dates, and reproductive output in ash-throated flycatchers suggests a higher tolerance for changing environmental conditions in this species. This is consistent with the population increases reported for flycatchers in areas experiencing dramatic climate changes.

Timing of vegetation sampling does not influence associations between visual obstruction and turkey nest survival in a montane forest.

Evaluating relationships between ecological processes that occur concurrently is complicated by the potential for such processes to covary. Ground‐nesting birds rely on habitat characteristics that provide visual and olfactory concealment from predators; this protection often is provided by vegetation at the nest site. Recently, researchers have raised concern that measuring vegetation characteristics at nest fate (success or failure) introduces a bias, as vegetation at successful nests is measured later in the growing season (and has more time to grow) compared with failed nests. In some systems, this bias can lead to an erroneous conclusion that plant height is positively associated with nest survival. However, if the features that provide concealment are invariant during the incubation period, no bias should be expected, and the timing of measurement is less influential. We used data collected from 98 nests to evaluate whether there is evidence that such a bias exists in a study of wild turkey (Meleagris gallopavo) nesting in a montane forest ecosystem. We modeled nest survival as a function of visual obstruction and other covariates of interest. At unsuccessful nests, we collected visual obstruction readings at both the date of nest failure and the projected hatch date and compared survival estimates generated using both sets of vegetation data. In contrast to studies in grassland and shrubland systems, we found little evidence that the timing of vegetation sampling influenced conclusions regarding the association between visual obstruction and nest survival; model selection and estimates of nest survival were similar regardless of when vegetation data were collected. The dominant hiding cover at most of our nests was provided by evergreen shrubs; retention of leaves and slow growth of these plants likely prevent appreciable changes in visual obstruction during the incubation period. When considered in aggregate with a growing body of literature, our results suggest that the influence of timing of vegetation sampling depends on the study system. When designing future studies, investigators should carefully consider the type of structures that provide nest concealment and whether plant phenology is confounded with nest survival.

Early life history of tropical freshwater eels (Anguilla spp.) recruiting to Viti Levu, Fiji Islands, in the western South Pacific

The oceanic early life histories of three species of tropical anguillid glass eels, namely Anguilla marmorata, Anguilla megastoma and Anguilla obscura, recruiting to Viti Levu, Fiji Islands, in the western South Pacific, were studied using otolith microstructures of 94 individuals. A. megastoma had the shortest leptocephalus duration, age at recruitment and metamorphosis stage (mean±s.d. 104.7±7.2, 141.3±8.7 and 36.6±8.5 days respectively), followed by A. marmorata (September–October recruitment peak: 113.0±11.9, 115.1±8.3 and 39.2±11.1 days respectively; April recruitment peak: 152.2±13.5, 154.0±12.5 and 38.9±10.1 days respectively) and A. obscura (118.0±10.2, 168.4±16.5 and 49.6±12.5 days respectively). A. obscura also had the shortest oceanic glass eel duration of (12.2±3.4 days), followed by both peaks of A. marmorata (23.3±3.2 and 20.2±3.3 days) and A. megastoma (20.7±6.7 days). Otolith increment rates during the leptocephalus stage did not differ significantly among the three species, but there were significant differences between the leptocephalus duration and metamorphosis stage of A. megastoma compared with A. marmorata and A. obscura, as well as in the oceanic glass eel duration of A. obscura compared with A. marmorata and A. megastoma. There were also significant differences in the age at recruitment among all three species. Back-calculated hatch dates suggest separate peak seasonal spawning periods for each of the three species.