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At least 775 records · Page 43Linked to original sources

USGS2015

Evidence of counter-gradient growth in western pond turtles ( Actinemys marmorata ) across thermal gradients

Counter-gradient growth, where growth per unit temperature increases as temperature decreases, can reduce the variation in ectothermic growth rates across environmental gradients. Understanding how ectothermic species respond to changing temperatures is essential to their conservation and management due to human-altered habitats and changing climates. Here, we use two contrasting populations of western pond turtles ( Actinemys marmorata ) to model the effect of artificial and variable temperature regimes on growth and age at reproductive maturity. The two populations occur on forks of the Trinity River in northern California, U.S.A. The South Fork Trinity River (South Fork) is unregulated, while the main stem of the Trinity River (Main Stem) is dammed and has peak seasonal temperatures that are approximately 10 °C colder than the South Fork. Consistent with other studies, we found reduced annual growth rates for turtles in the colder Main Stem compared to the warmer South Fork. The South Fork population matured approximately 9 year earlier, on average, and at a larger body size than the Main Stem population. When we normalised growth rates for the thermal opportunity for growth using water-growing degree-days (GDD), we found the reverse for growth rates and age at reproductive maturity. Main Stem turtles grew approximately twice as fast as South Fork turtles per GDD. Main Stem turtles also required approximately 50% fewer GDD to reach their smaller size at reproductive maturity compared to the larger South Fork turtles. We found we could accurately hindcast growth rates based on water temperatures estimated from the total volume of discharge from the dam into the Main Stem, providing a management tool for predicting the impacts of the dam on turtle growth rates. Given the importance of size and age at reproductive maturity to population dynamics, this information on counter-gradient growth will improve our ability to understand and predict the consequences of dam operations for downstream turtle populations.

California↗

USGS2015

Depth of artificial Burrowing Owl burrows affects thermal suitability and occupancy

Many organizations have installed artificial burrows to help bolster local Burrowing Owl ( Athene cunicularia ) populations. However, occupancy probability and reproductive success in artificial burrows varies within and among burrow installations. We evaluated the possibility that depth below ground might explain differences in occupancy probability and reproductive success by affecting the temperature of artificial burrows. We measured burrow temperatures from March to July 2010 in 27 artificial burrows in southern California that were buried 15–76 cm below the surface (measured between the surface and the top of the burrow chamber). Burrow depth was one of several characteristics that affected burrow temperature. Burrow temperature decreased by 0.03°C per cm of soil on top of the burrow. The percentage of time that artificial burrows provided a thermal refuge from above-ground temperature decreased with burrow depth and ranged between 50% and 58% among burrows. The percentage of time that burrow temperature was optimal for incubating females also decreased with burrow depth and ranged between 27% and 100% among burrows. However, the percentage of time that burrow temperature was optimal for unattended eggs increased with burrow depth and ranged between 11% and 95% among burrows. We found no effect of burrow depth on reproductive success across 21 nesting attempts. However, occupancy probability had a non-linear relationship with burrow depth. The shallowest burrows (15 cm) had a moderate probability of being occupied (0.46), burrows between 28 and 40 cm had the highest probability of being occupied (>0.80), and burrows >53 cm had the lowest probability of being occupied (<0.43). Burrowing Owls may prefer burrows at moderate depths because these burrows provide a thermal refuge from above-ground temperatures, and are often cool enough to allow females to leave eggs unattended before the onset of full-time incubation, but not too cool for incubating females that spend most of their time in the burrow during incubation. Our results suggest that depth is an important consideration when installing artificial burrows for Burrowing Owls. However, additional study is needed to determine the possible effects of burrow depth on reproductive success and on possible tradeoffs between the effects of burrow depth on optimal temperature and other factors, such as minimizing the risk of nest predation.

Journal of Field Ornithology↗

USGS2019

Comparative breeding ecology of Mississippi Kites in urban and exurban areas of West Texas

Birds of prey are becoming increasingly common occupants of urbanized settings, but the comparative benefits or detriments they experience in urban environs compared to exurban areas are poorly understood. We examined the reproductive success and phenology of Mississippi Kites ( Ictinia mississippiensis ) nesting concurrently in urban and exurban areas in west Texas during the 2010–2012 and 2014 breeding seasons. Our objective was to better understand the reproductive advantages or disadvantages that kites may experience by nesting in urban areas rather than exurban areas. We calculated annual productivity, estimated daily survival rates of nests, and estimated hatch dates. Kites produced 0.52 fledglings per urban nesting attempt and 0.33 fledglings per exurban nesting attempt. We found no difference in the mean number of young that fledged from successful urban (1.06) and exurban (1.07) nests, but kites in urban areas had greater nesting success within years than those in exurban areas. Both heat and drought were associated with low productivity and success in both areas, but the urban landscape appears to have provided some buffer to their effects. These factors may have had direct (e.g., exposure) or indirect (e.g., negative influences on prey availability) influences on reproductive success. Counter to previous studies of urban raptors, we found that exurban kites nested significantly earlier than urban kites. This may be linked to differences in environmental conditions and prey availability between the areas. Our results suggest that urban areas provide a reproductive advantage for Mississippi Kites in terms of facilitating an overall higher nesting success, but this does not translate into increased productivity for successful pairs. Further, our data suggest that, although urban areas may buffer species from drought or heat, that buffer can be breached during severe conditions.

Texas↗

USGS2014

An experimental investigation of chemical communication in the polar bear

The polar bear ( U rsus maritimus ), with its wide-ranging movements, solitary existence and seasonal reproduction, is expected to favor chemosignaling over other communication modalities. However, the topography of its Arctic sea ice habitat is generally lacking in stationary vertical substrates routinely used for targeted scent marking in other bears. These environmental constraints may have shaped a marking strategy, unique to polar bears, for widely dispersed continuous dissemination of scent via foot pads. To investigate the role of chemical communication, pedal scents were collected from free-ranging polar bears of different sex and reproductive classes captured on spring sea ice in the Beaufort and Chukchi seas, and presented in a controlled fashion to 26 bears in zoos. Results from behavioral bioassays indicated that bears, especially females, were more likely to approach conspecific scent during the spring than the fall. Male flehmen behavior, indicative of chemosignal delivery to the vomeronasal organ, differentiated scent donor by sex and reproductive condition. Histologic examination of pedal skin collected from two females indicated prominent and profuse apocrine glands in association with large compound hair follicles, suggesting that they may produce scents that function as chemosignals. These results suggest that pedal scent, regardless of origin, conveys information to conspecifics that may facilitate social and reproductive behavior, and that chemical communication in this species has been adaptively shaped by environmental constraints of its habitat. However, continuously distributed scent signals necessary for breeding behavior may prove less effective if current and future environmental conditions cause disruption of scent trails due to increased fracturing of sea ice.

Journal of Zoology↗

USGS2015

A plant toxin mediated mechanism for the lag in snowshoe hare population recovery following cyclic declines

A necessary condition for a snowshoe hare population to cycle is reduced reproduction after the population declines. But the cause of a cyclic snowshoe hare population's reduced reproduction during the low phase of the cycle, when predator density collapses, is not completely understood. We propose that moderate-severe browsing by snowshoe hares upon preferred winter-foods could increase the toxicity of some of the hare's best winter-foods during the following hare low, with the result being a decline in hare nutrition that could reduce hare reproduction. We used a combination of modeling and experiments to explore this hypothesis. Using the shrub birch Betula glandulosa as the plant of interest, the model predicted that browsing by hares during a hare cycle peak, by increasing the toxicity B. glandulosa twigs during the following hare low, could cause a hare population to cycle. The model's assumptions were verified with assays of dammarane triterpenes in segments of B. glandulosa twigs and captive hare feeding experiments conducted in Alaska during February and March 1986. The model's predictions were tested with estimates of hare density and measurements of B. glandulosa twig growth made at Kluane, Yukon from 1988–2008. The empirical tests supported the model's predictions. Thus, we have concluded that a browsing-caused increase in twig toxicity that occurs during the hare cycle's low phase could reduce hare reproduction during the low phase of the hare cycle.

Yukon↗

USGS2003

Population dynamics of hispid cotton rats (Sigmodon hispidus) across a nitrogen-amended landscape

We conducted a mark-recapture experiment to examine the population dynamics of hispid cotton rats (Sigmodon hispidus) in response to low-level nitrogen amendments (16.4 kg nitrogen/ha per year) and exclosure fencing in an old-field grassland. The experimental design consisted of sixteen 0.16-ha plots with 4 replicates of each treatment combination. We predicted that densities, reproductive success, movement probabilities, and survival rates of cotton rats would be greater on nitrogen-amended plots because of greater aboveground biomass and canopy cover. Population densities of cotton rats tended to be highest on fenced nitrogen plots, but densities on unfenced nitrogen plots were similar to those on control and fenced plots. We observed no distinct patterns in survival rates, reproductive success, or movement probabilities with regard to nitrogen treatments. However, survival rates and reproductive success tended to be higher for cotton rats on fenced plots than for those on unfenced plots and this was likely attributable to decreased predation on fenced plots. As low-level nitrogen amendments continue to be applied, we predict that survival, reproduction, and population-growth rates of cotton rats on control plots, especially fenced plots with no nitrogen amendment, will eventually exceed those on nitrogen-amended plots as a result of higher plant-species diversity, greater food availability, and better quality cover.

Canadian Journal of Zoology↗

USGS2025

Identifying presence or absence of grizzly and polar bear cubs from the movements of adult females with machine learning

Background Information on reproductive success is crucial to understanding population dynamics but can be difficult to obtain, particularly for species that birth while denning. For grizzly ( Ursus arctos ) and polar bears ( U. maritimus ), den visits are impractical because of safety and logistical considerations. Reproduction is typically documented through direct observation, which can be difficult, costly, and often occurs long after den departure. Reproduction could be documented remotely, however, from post-denning movement data if discernable differences exist between females with and without cubs. Methods We trained support vector machines (SVMs) with eight variables derived from telemetry data of female grizzly (2000–2022) and polar bears (1985–2016) with or without cubs during seven periods with lengths ranging from 5 to 60 days starting at den departure. We assessed SVM classification accuracy by withholding two samples (one cub-present, one cub-absent), training SVMs with the remaining data, predicting classification of the withheld samples, and repeating this process for each sample combination. Additionally, we evaluated how classification accuracy for grizzly bears was influenced by sample size, length of the post-departure period, and frequency of standardized location estimates. Results Accuracy of predicting cub presence or absence was 87% for grizzly bears with only 5 days of post-departure data and increased to a maximum of 92% with 20 days of data. For polar bears, accuracy was 86% at 5 days post-departure and increased to a maximum of 93% at 50 days. Classification accuracy for grizzly bears increased from 76 to 90% when sample size increased from 10 to 30 bears while holding period length constant (30 days) but did not increase at larger sample sizes. When sample size was held constant, increasing the length of the post-departure period did not affect classification accuracy markedly. Conclusion Presence or absence of grizzly and polar bear cubs can be identified with high accuracy even when SVM models are trained with limited data. Detecting cub presence or absence remotely could improve estimates of reproductive success and litter survival, enhancing our understanding of factors affecting cub recruitment.

Alaska, Idaho, Montana, Wyoming↗

USGS2017

Advancing the match-mismatch framework for large herbivores in the Arctic: Evaluating the evidence for a trophic mismatch in caribou

Climate-induced shifts in plant phenology may adversely affect animals that cannot or do not shift the timing of their reproductive cycle. The realized effect of potential trophic “mismatches” between a consumer and its food varies with the degree to which species rely on dietary income and stored capital. Large Arctic herbivores rely heavily on maternal capital to reproduce and give birth near the onset of the growing season but are they vulnerable to trophic mismatch? We evaluated the long-term changes in the temperatures and characteristics of the growing seasons (1970–2013), and compared growing conditions and dynamics of forage quality for caribou at peak parturition, peak lactation, and peak forage biomass, and plant senescence between two distinct time periods over 36 years (1977 and 2011–13). Despite advanced thaw dates (7−12 days earlier), increased growing season lengths (15−21 days longer), and consistent parturition dates, we found no decline in forage quality and therefore no evidence within this dataset for a trophic mismatch at peak parturition or peak lactation from 1977 to 2011–13. In Arctic ungulates that use stored capital for reproduction, reproductive demands are largely met by body stores deposited in the previous summer and autumn, which reduces potential adverse effects of any mismatch between food availability and timing of parturition. Climate-induced effects on forages growing in the summer and autumn ranges, however, do correspond with the demands of female caribou and their offspring to gain mass for the next reproductive cycle and winter. Therefore, we suggest the window of time to examine the match-mismatch framework in Arctic ungulates is not at parturition but in late summer-autumn, where the multiplier effects of small changes in forage quality are amplified by forage abundance, peak forage intake, and resultant mass gains in mother-offspring pairs.

Alaska↗

USGS2021

Heterospecific pollination by an invasive congener threatens the native American bittersweet, Celastrus scandens

Invasive plants have the potential to interfere with native species’ reproductive success through a number of mechanisms, including heterospecific pollination and hybridization. This study investigated reproductive interactions between a native North American woody vine (American bittersweet, Celastrus scandens ) and an introduced congener (oriental bittersweet, C . orbiculatus ). The decline of C . scandens in the eastern portion of its range is coincident with the introduction and spread of C . orbiculatus , and the two species are known to hybridize. The relationship between proximity and floral production of conspecific and heterospecific males on fertilization and hybridization rates was measured at a field site in northwestern Indiana, USA where both species occur and reproduce. We found that the invasive vine had an extreme advantage in both male and female floral production, producing nearly 200 times more flowers per staminate plant and 65 times more flowers per pistillate plant than the native. Using nuclear microsatellite DNA markers we found that hybridization rates were asymmetric; 39% of the C . scandens seeds tested were hybrids, compared to only 1.6% of C . orbiculatus seeds. The asymmetric hybridization rates were likely not solely due to greater abundance of C . orbiculatus pollen because experimental hand crosses revealed that C . scandens had a higher rate (41%) of heterospecific fertilization than C . orbiculatus (2.4%). We previously reported that few hybrids were observed in the wild, and hybrids had greatly reduced fecundity. Thus, in our system, the threat posed by heterospecific pollen is not replacement by hybrids or introgression, but rather asymmetric reproductive interference. Reproductive interference extended to distances as great as 100 meters, thus, efforts to conserve the native species must reduce its exposure to C . orbiculatus over a relatively large spatial scale.

Indiana↗

USGS2007

Relative abundance, site fidelity, and survival of adult lake trout in Lake Michigan from 1999 to 2001: Implications for future restoration strategies

We compared the relative abundance of lake trout Salvelinus namaycush spawners in gill nets during fall 1999–2001 in Lake Michigan at 19 stocked spawning sites with that at 25 unstocked sites to evaluate how effective site-specific stocking was in recolonizing historically important spawning reefs. The abundance of adult fish was higher at stocked onshore and offshore sites than at unstocked sites. This suggests that site-specific stocking is more effective at establishing spawning aggregations than relying on the ability of hatchery-reared lake trout to find spawning reefs, especially those offshore. Spawner densities were generally too low and too young at most sites to expect significant natural reproduction. However, densities were sufficiently high at some sites for reproduction to occur and therefore the lack of recruitment was attributable to other factors. Less than 3% of all spawners could have been wild fish, which indicates that little natural reproduction occurred in past years. Wounding by sea lamprey Petromyzon marinus was generally lower for Seneca Lake strain fish and highest for strains from Lake Superior. Fish captured at offshore sites in southern Lake Michigan had the lowest probability of wounding, while fish at onshore sites in northern Lake Michigan had the highest probability. The relative survival of the Seneca Lake strain was higher than that of the Lewis Lake or the Marquette strains for the older year-classes examined. Survival differences among strains were less evident for younger year-classes. Recaptures of coded-wire-tagged fish of five strains indicated that most fish returned to their stocking site or to a nearby site and that dispersal from stocking sites during spawning was about 100 km. Restoration strategies should rely on site-specific stocking of lake trout strains with good survival at selected historically important offshore spawning sites to increase egg deposition and the probability of natural reproduction in Lake Michigan.

North American Journal of Fisheries Management↗

USGS2021

Genome-wide SNP analysis reveals multiple paternity in Burmese pythons invasive to the Greater Florida Everglades

Reproductive strategies are an essential component of invasion ecology that influence invasion success and rates of population growth. Burmese Pythons ( Python bivittatus ) are large constrictor snakes that were introduced to the Greater Everglades Ecosystem of southern Florida, USA, from Asia. Since their introduction, these giant constrictors have spread throughout wetlands of southern Florida while increasing in abundance and causing declines in the native species upon which they prey. Multiple paternity in reproduction could facilitate invasion success by increasing the genetic diversity produced within each reproductive event. We used Diversity Arrays Technology genome-wide genotyping to assess multiple paternity in the progeny of wild Burmese Pythons in Florida. We analyzed >4,000 single nucleotide polymorphisms from 153 neonates belonging to 4 clutches collected in southwestern Florida. Complementary hierarchical and K -means clustering analyses of the genetic distances within clutches revealed that three clutches were each fertilized by two sires, with a fourth fertilized by a single sire. The proportions of offspring attributable to each sire within multiple paternity clutches ranged from nearly even to highly skewed. Analysis of multivariate dispersion showed significantly increased genetic variability in the multiple paternity clutches. These results improve our understanding of the reproductive strategy and invasion potential of a giant constrictor with significant ecological impacts.

Florida↗

USGS2007

Iteroparity in the variable environment of the salamander Ambystoma tigrinum

Simultaneous estimation of survival, reproduction, and movement is essential to understanding how species maximize lifetime reproduction in environments that vary across space and time. We conducted a four-year, capture–recapture study of three populations of eastern tiger salamanders ( Ambystoma tigrinum tigrinum ) and used multistate mark–recapture statistical methods to estimate the manner in which movement, survival, and breeding probabilities vary under different environmental conditions across years and among populations and habitats. We inferred how individuals may mitigate risks of mortality and reproductive failure by deferring breeding or by moving among populations. Movement probabilities among populations were extremely low despite high spatiotemporal variation in reproductive success and survival, suggesting possible costs to movements among breeding ponds. Breeding probabilities varied between wet and dry years and according to whether or not breeding was attempted in the previous year. Estimates of survival in the nonbreeding, forest habitat varied among populations but were consistent across time. Survival in breeding ponds was generally high in years with average or high precipitation, except for males in an especially ephemeral pond. A drought year incurred severe survival costs in all ponds to animals that attempted breeding. Female salamanders appear to defer these episodic survival costs of breeding by choosing not to breed in years when the risk of adult mortality is high. Using stochastic simulations of survival and breeding under historical climate conditions, we found that an interaction between breeding probabilities and mortality limits the probability of multiple breeding attempts differently between the sexes and among populations.

Virginia↗

USGS2011

Stochastic population dynamics in populations of western terrestrial garter snakes with divergent life histories

Comparative evaluations of population dynamics in species with temporal and spatial variation in life‐history traits are rare because they require long‐term demographic time series from multiple populations. We present such an analysis using demographic data collected during the interval 1978–1996 for six populations of western terrestrial garter snakes ( Thamnophis elegans ) from two evolutionarily divergent ecotypes. Three replicate populations from a slow‐living ecotype, found in mountain meadows of northeastern California, were characterized by individuals that develop slowly, mature late, reproduce infrequently with small reproductive effort, and live longer than individuals of three populations of a fast‐living ecotype found at lakeshore locales. We constructed matrix population models for each of the populations based on 8–13 years of data per population and analyzed both deterministic dynamics based on mean annual vital rates and stochastic dynamics incorporating annual variation in vital rates. (1) Contributions of highly variable vital rates to fitness (λ s ) were buffered against the negative effects of stochastic variation, and this relationship was consistent with differences between the meadow (M‐slow) and lakeshore (L‐fast) ecotypes. (2) Annual variation in the proportion of gravid females had the greatest negative effect among all vital rates on λ s . The magnitude of variation in the proportion of gravid females and its effect on λ s was greater in M‐slow than L‐fast populations. (3) Variation in the proportion of gravid females, in turn, depended on annual variation in prey availability, and its effect on λ s was 4–23 times greater in M‐slow than L‐fast populations. In addition to differences in stochastic dynamics between ecotypes, we also found higher mean mortality rates across all age classes in the L‐fast populations. Our results suggest that both deterministic and stochastic selective forces have affected the evolution of divergent life‐history traits in the two ecotypes, which, in turn, affect population dynamics. M‐slow populations have evolved life‐history traits that buffer fitness against direct effects of variation in reproduction and that spread lifetime reproduction across a greater number of reproductive bouts. These results highlight the importance of long‐term demographic and environmental monitoring and of incorporating temporal dynamics into empirical studies of life‐history evolution.

California↗

USGS2005

A field assessment of long-term laboratory sediment toxicity tests with the amphipod Hyalella azteca

Response of the amphipod Hyalella azteca exposed to contaminated sediments for 10 to 42 d in laboratory toxicity tests was compared to responses observed in controlled three-month invertebrate colonization exposures conducted in a pond. Sediments evaluated included a sediment spiked with dichlorodiphenyldichloroethane (DDD) or dilutions of a field sediment collected from the Grand Calumet River (GCR) in Indiana (USA) (contaminated with organic compounds and metals). Consistent effects were observed at the highest exposure concentrations (400 ??g DDD/goc [DDD concentrations normalized to grams of organic carbon (goc) in sedimentl or 4% GCR sediment) on survival, length, and reproduction of amphipods in the laboratory and on abundance of invertebrates colonizing sediments in the field. Effect concentrations for DDD observed for 10-d length and 42-d reproduction of amphipods (e.g., chronic value [ChV] of 66 ??g DDD/goc and 25% inhibition concentration [IC25] of 68 ??g DDD/goc for reproduction) were similar to the lowest effect concentrations for DDD measured on invertebrates colonizing sediment the field. Effect concentrations for GCR sediment on 28-d survival and length and 42-d reproduction and length of amphipods (i.e., ChVs of 0.20-0.66% GCR sediment) provided more conservative effect concentrations compared to 10-d survival or length of amphipods in the laboratory or the response of invertebrates colonizing sediment in the field (e.g., ChVs of 2.2% GCR sediment). Results of this study indicate that use of chronic laboratory toxicity tests with H. azteca and benthic colonization studies should be used to provide conservative estimates of impacts on benthic communities exposed to contaminated sediments. Bioaccumulation of DDD by oligochaetes colonizing the DDD-spiked sediment was similar to results of laboratory sediment tests previously conducted with the oligochaete Lumbriculus variegates, confirming that laboratory exposures can be used to estimate bioaccumulation by oligochaetes exposed in the field. ?? 2005 SETAC.

Environmental Toxicology and Chemistry↗

USGS2006

Taxonomic and geographic variation in oviposition by tailed frogs ( Ascaphus spp )

Tailed frogs ( Ascaphus spp.) oviposit in cryptic locations in streams of the Pacific Northwest and Rocky Mountains. This aspect of their life history has restricted our understanding of their reproductive ecology. The recent split of A. montanus in the Rocky Mountains from A. truei was based on molecular differentiation, and comparisons of their ecology are limited. Our objectives were to provide a range-wide summary of information on Ascaphus oviposition, compare some aspects of the reproductive ecology of the 2 species, and examine geographic variation in their reproductive traits. Reproductive ecology of the 2 species differed. Ascaphus truei had smaller clutches, oviposited later in the summer, and had a longer duration of oviposition than A. montanus . A greater number of communal oviposition sites were attributed to A. montanus . These ecological differences support the recent taxonomic revision of Ascaphus and suggest that different management strategies may be necessary for each species where conservation is a priority.

Northwestern Naturalist↗

USGS1976

Influence of stimuli from populations of Peromyscus leucopus on maturation of young

The effects of stimuli associated with conspecific laboratory populations on parameters of sexual maturation in Peromyscus leucopus were examined. Beginning at birth, experimental litters were exposed to the constant infusion of urine, feces, and other material from the populations through a metabolism funnel into their cages. As evidenced by age at first vaginal estrus, experimental females matured later than controls. They also had lighter weight reproductive organs. Testis weights were much greater in control than experimental males. These data suggest that stimuli from populations of P. leucopus can inhibit reproductive maturation of conspecifics. In view of the well-documented effects of chemical stimuli on reproductive maturation and function in other rodents, it is suggested that chemical stimuli in the feces, urine, or from other sources mediated the reproductive inhibition observed in this study.

Journal of Mammalogy↗

USGS1977

Energy allocation patterns of a sprouting and nonsprouting species of Arctostaphylos in the California chaparral

The r- and K-selection theory was used to generate testable hypotheses about patterns of energy allocation in two chaparral shrubs of different reproductive strategies. Terminal-branchlet vegetative and reproductive biomass of the nonsprouting Arctostaphylos glauca and the sprouting A. glandulosa were sampled in a 23-year-old and a 90-year-old stand of chaparral to test the predictions that: (1) the terminal vegetative growth (g dry weight/m 2 of areal coverage) would be equal in the two species, in both stands; (2) oven dry weight (g) of reproductive parts/m 2 of areal coverage would be greater in A. glauca than in A. glandulosa in both aged populations; (3) allocation to reproductive parts by the shrubs in the 23-year-old stand would be greater than (or equal to) that of the 90-year-old shrubs. The amount of terminal vegetative growth was equal for both species in the 23-year-old and the 90-year-old stands. There was no statistically significant difference in the weight of fruits produced by the two species in the 23-year-old stand. However, fruit production by A. glauca was significantly greater than by A. glandulosa in the 90-year-old stand. Fruit production was also significantly greater for the older A. glauca shrubs than for those in the 23-year-old stand. The relationships of rainfall pattern and age of shrubs to fruit production are discussed.

California↗

USGS1997

Wetland use, settling patterns, and recruitment in mallards

The correlation between number of May ponds in the Prairie Pothole Region (PPR) of North America and size of the continental mallard (Anas platyrhynchos) breeding population the following spring weakened from the 1950s to the 1980s, suggesting possible changes in suitability of prairie ponds for meeting reproductive needs. We studied wetland use and preferences of radioequipped female mallards by reproductive stage (1988-90) in eastern North Dakota and westcentral Minnesota and evaluated effect of land use on pair distribution in eastern North Dakota (1987-91). May pond density varied among years and study areas, with changes in number of temporary and seasonal ponds accounting for 93% of variation in total ponds. During all reproductive stages, semipermanent basins were used most by females, but temporary and seasonal ponds were preferred during prenesting and egg production. Accounting for number of relocations, number of ponds used varied by year, by reproductive stage and with pond density during egg production. Numbers of breeding mallard pairs in stratum 46 in eastern North Dakota increased as May ponds increased from 1963 to 1985, but 33,659 fewer breeding pairs on average were present in 1971-85 than in 1963-70. Number of breeding pairs declined relative to May ponds from the 1960s to the 1980s, probably because fewer pairs settle in temporary and seasonal ponds as the percent of landscape in cropland increases. Waterfowl managers in the PPR should target efforts to increase duck production on landscapes where non-cropped temporarily and seasonally flooded wetland habitats are plentiful, thereby increasing cost effectiveness of management actions taken to increase nest success rate.

Journal of Wildlife Management↗