I designed a suite of studies in coordination with Utah Division of Wildlife Resources (UDWR) to evaluate waterfowl use of the GSL in winter and ecological aspects associated with GSL use. These studies provided insight into key information gaps previously identified by UDWR regarding management of GSL resources. Population surveys indicated total duck abundance was low when GSL surface elevations were low and wetland resources diminished because of persistent drought in the system. Also, ducks appear to use hypersaline parts of GSL more when freshwater habitats are limited from either drought or ice conditions. Common goldeneye, northern shoveler, and green-winged teal exhibited the most use of hypersaline areas. Dietary evaluations indicated all three species feed on hypersaline invertebrates from GSL to meet energetic and nutritional needs in winter. Brine shrimp cysts were important foods for northern shoveler and green-winged teal. Fat levels of ducks are important determinants of survival and fitness. Fat reserves of goldeneye were generally lower in the winter when both GSL and wetland habitat resources were lower. Results suggest brine fly larvae productivity, freshwater habitat availability, and temperature and wind speed likely play a more prominent role in goldeneye fat reserves than osmoregulation. Also, common goldeneye and northern shoveler using the GSL apparently accumulated biologically concerning amounts of mercury and selenium during winter. However, further research is needed to evaluate the effect of these elements on GSL ducks.

Age and growth were determined from otoliths for 181 juvenile bluefish, Pomatomus saltatrix, collected using a variety of gear in northeast Florida during 2003 and 2005. Three distinct cohorts were identified recruiting to the near shore waters during spring, summer and fall. Growth rates were high regardless of cohort or season. To compare pre- and post-recruitment growth rates, models were fit to individual growth trajectories using change point analysis. Post-estuarine growth rates were generally higher. Growth rates and hatching times were within the range of those obtained in other bluefish studies conducted at higher latitudes. As this is the only area where winter recruitment of bluefish has been observed, coastal Florida habitats may be essential for the bluefish stock and will need to be carefully monitored in future studies. A technique to estimate the lipid content of bluefish was developed using fat stage (subjectively assigned based on mesenteric fat around the stomach), fish length, and fish weight. A highly significant relationship was observed between fat stage and lipid content in a generalized linear model. The visual lipid content technique provides rapid results, is inexpensive and could be easily implemented into current fisheries sampling methods. Total lipids were also extracted from potential bluefish prey species collected during sampling. Prey lipids ranged from 0.88% to 19.52%. Regular prey species from the MAB; Atlantic silverside and bay anchovy contained 3.49% and 3.19% mean lipids respectively. Highest lipid content was observed in mullet (Mugil spp.) (19.52%) and was significantly higher than other available prey species. A previous study indentified a decline in bluefish lipids as winter progressed as well as a prey preference for mullet. We propose mullet are the preferred prey choice due to their high lipid content.

Human activities such as fossil fuel combustion and deforestation have increased atmospheric concentrations of carbon dioxide, reactive nitrogen, and other greenhouse gases. As a result, Earth's surface has warmed by 0.85 °C since the pre-industrial era and will continue to warm. Many northern latitude temperate forest ecosystems mitigate the effects of both elevated carbon dioxide and atmospheric nitrogen deposition through retention of carbon and nitrogen in plants and soils. However, the continued ability of these ecosystems to store carbon and nitrogen will be altered with continued climate change. Warmer winters will lead to reduced depth and duration of snowpack, which insulates soils from cold winter air. Climate change over the next century will therefore affect soil temperatures in northern temperate forests in opposing directions across seasons, with warmer soils in the growing season and colder, more variable soil temperatures in winter. Warmer growing seasons generally increase ecosystem uptake and storage of carbon and nitrogen, whereas a smaller snowpack and colder soils in winter reduce rates of ecosystem nutrient cycling and plant growth. My dissertation aims to understand how climate change in the growing season and winter interact to affect function and nitrogen cycling in northern hardwood forest ecosystems. I accomplished this goal through formal literature review and two climate change manipulation experiments at Hubbard Brook Experimental Forest, NH. I found that although 67% of climate change experiments were conducted in seasonally snow covered ecosystems, only 14% take into account the effects of distinct climate changes in winter. By simulating climate change across seasons, I demonstrated that changes in nitrogen cycling caused by increased soil freezing in winter are not offset by warming in the growing season. Moreover, shifts in plant function due to winter climate change are mediated through a combination of changes in snow depth, soil temperature, and plant-herbivore interactions that differentially affect above- and belowground plant components. These results would not be evident from examining climate change in either the growing season or winter alone and demonstrate the need for considering seasonally distinct climate change to determine how nitrogen and carbon cycling will change in the future.

The world's biodiversity is concentrated in tropical ecosystems, yet tropical forests are being converted for agriculture at a rapid rate. I evaluated the potential of an alternative coffee production system known as Integrated Open Canopy (IOC) to contribute to avian conservation. This study was conducted from 2005-2010 in the Cordillera de Tilarán, Costa Rica. My results indicate that species richness of forest-dependent birds was higher in IOC farms than in shade coffee farms, and was comparable to secondary forest sites. There was no difference in species richness of Neotropical-Nearctic migrants between IOC and shade coffee farms. Overall similarity was higher between IOC farms and primary forest than between shade coffee farms and primary forest. he golden-winged warbler Vermivora chrysoptera is a declining Neotropical-Nearctic migrant bird, yet little is known about its non-breeding season ecology and demographics. I found that golden-winged warbler abundance was highest at intermediate precipitation levels found at middle elevations (1000-1200 m) of the Pacific slope, but they were absent from the dry forests at lower elevations on the Pacific slope. Abundance peaked in forests with canopy heights of 22 m, and was positively related to the quantity of hanging dead leaves. Radio-telemetry data indicated that golden-winged warblers used microhabitat features characteristic of disturbance more frequently than expected by chance. Selection of these microhabitat features was related to their highly specialized dead-leaf foraging behavior, which may also have contributed to their high degrees of site fidelity, mixed-species flock attendance, and territoriality. These behaviors have important conservation implications because they constrain density, and thus could affect carrying capacity. Population dynamics were characterized by estimating plot-level and individual-level apparent survival and recruitment rates within and among non-breeding seasons. Both levels of analysis suggested that recruitment was too low to offset mortalities within this study area. This study indicates that increasing forest cover in tropical agricultural landscapes may be the most effective way of providing habitat for bird species of high conservation concern, including the golden-winged warbler. Integrated open canopy coffee production is one option for achieving this goal because it provides a financial incentive to protect or restore forest.

Small birds likely face energetic challenges in temperate zone winters posed by cold weather coupled with food scarcity. These challenges are often assumed to occur, but are rarely experimentally tested. I hypothesized that the naturally occurring, lower abundances of food in temperate zone winters limit a bird's ability to acquire optimal energy and ultimately limit fitness. In this dissertation, I show that supplementation of food decreased mortality and improved traits potentially associated with future reproductive success of wild swamp sparrows (Melospiza georgiana), supporting the hypothesis that winter food abundance limits fitness. These results come from a replicated and controlled food supplementation experiment conducted over three years. First, I demonstrated that following food addition, immigration increased, leading to higher densities, and that all age/sex classes experienced higher survival and maintained larger energy reserves (Chapter I). Survival was positively related to energy reserves, indicating that food availability limits survival through a bird's ability to maintain sufficient fat. In addition to causing mortality in winter, food limitation of energy reserves may carry over to affect future reproductive success by influencing timing of preparations for breeding, including migration. In Chapter II, I show that swamp sparrows decreased fat reserves over each winter, despite unlimited food availability, indicating that they adaptively regulated fat reserves, potentially to balance starvation and depredation risks. Fat reserves of control birds tracked recent temperature and control birds lost muscle throughout the winter, indicating that they were limited by food and were unable to reach optimal fat levels on a daily basis. These results suggest that limitation of energy reserves by food availability can be influenced by temperature and predator abundance. Lastly, I demonstrated that food abundance limits the timing of molt in the wild (Chapter III), an unprecedented finding. Because molt, migration, and breeding typically do not overlap, early molt might lead to earlier migration and breeding. Therefore, we hypothesize that timing of molt is another mechanism by which winter food abundance can limit reproductive success. These results provide strong evidence that food availability can limit wintering temperate migrants in a variety of ways. / Ph. D.

Abstract Despite the great amount of in-stream restorations conducted in the past decades there is still a disturbing lack of knowledge about the outcome of these measures. The overall goal of this study was to assess the effect of enhanced streambed heterogeneity on the ecology of stream salmonids and stream retention efficiency. Substratum heterogeneity is often considered as one of the most important limiting factors for organisms living in running waters. Winter ecology of rivers has not been broadly studied regardless of the general belief that wintertime conditions strongly influence the survival and population size of stream salmonids. In an experimental study, the paucity of wintertime habitat in simplified channels caused temporary mass loss in age-0 trout. In late spring, channelized stream trout performed catch-up growth with potentially negative effects on long-term fitness. A management implication of this study is that increasing cover availability by in-stream restoration structures may enhance the long term success of juvenile salmonids although the short term effects were minor. Densities of salmon parr in the River Kiiminkijoki showed no response to streambed restoration. Suitable habitat area for salmon parr increased after restoration under summer conditions. However, restoration-induced benefits to winter habitats were marginal, with one study reach indicating even negative values. Most of the areas with good habitat values were located along river margins, indicating that restoration measures had only limited impact on the mid-sections of the river channel. Dredging of small streams may have caused depletion of allochthonous organic matter due to the reduction of retentive structures. In a leaf release experiment, moss cover enhanced retentiveness as well as did various restoration structures (boulders, large wood). Only a very high amount of wood clearly enhanced retention capacity. This underlines the importance of wood as an effective retention structure in headwater streams. This study indicates that habitat complexity as such may be less important than life-stage specific habitat requirements of fish (e.g. cover for overwintering salmonids). Importantly, restoration may only be successful if the measures used target the limiting factor(s) of the ecosystem or the species; for salmonids, habitat complexity does not seem to be this factor. / Tiivistelmä Uiton jälkeisten kunnostustoimenpiteiden määrä Suomessa on ollut huomattava, mutta vaikutusten arviointi, pelkästään kalastonkin kannalta, on jäänyt vähäiselle huomiolle. Tässä työssä selvitettiin kunnostusten merkitystä lohen ja taimenen poikasvaiheille, huomioiden etenkin pohjan rakenteellisen monimuotoisuuden vaikutus. Työssä selvitettiin myös kunnostusten vaikutuksia lehtikarikkeen pidätyskykyyn, joka on erityisesti latvapurojen ekosysteemien tärkeimpiä perustoimintoja. Lohikalojen talviekologinen tutkimus on viime aikoihin saakka ollut vähäistä, vaikka talviolosuhteiden uskotaan rajoittavan pohjoisten virtavesien eliöstön elinmahdollisuuksia. Kokeellisessa työssä rännimäisissä uomissa talvehtiminen aiheutti taimenenpoikasille tilapäisen painon alenemisen ja nopean kompensaatiokasvun loppukeväällä. Kompensaatiokasvu voi vaikuttaa negatiivisesti koko kalan eliniän, joten kunnostusten tuoma hyöty sopivien suojapaikkojen lisääntymisenä voi edesauttaa lohikalojen pitkäaikaista menestymistä. Kiiminkijoella lohenpoikasten tiheydet eivät muuttuneet kunnostuksen myötä ja vuosien välinen vaihtelu oli kuuden vuoden seurantajaksolla huomattavan suurta. Elinympäristömallinnuksen perusteella soveltuvan elinympäristön lisäys ei ollut merkittävää, koska etenkin talviaikaisten alueiden puute jäi huomattavaksi. Suurin osa soveltuvasta elinympäristöstä sijaitsi joen reuna-alueilla, joten kunnostusvaikutus joen keskiosaan jäi odotettua pienemmäksi. Uittoperkaus on voinut johtaa latvavesien ekosysteemien köyhtymiseen maalta tulevan orgaanisen aineksen pidättymiskyvyn vähentyessä. Kokeellisen työn perusteella kuitenkin nykypäivän tilanne vuosikymmeniä uiton loppumisen jälkeen osoittautui lähes yhtä pidättäväksi kuin nykyisin käytetyt kunnostusrakenteet (kivi tai puu). Kunnostusrakenteeseen tulisi lisätä huomattava määrä puuta, jotta lehtikarike pidättyisi korkeallakin virtaamatasolla. Tulosten perusteella elinympäristöjen muuttaminen monimuotoisemmiksi ei takaa kunnostustoimien onnistumista, sillä etenkin kalapopulaatioita rajoittavat yleensä useat tekijät. Jos kuitenkin elinympäristö on populaatiota rajoittava resurssi ja sitä pystytään lisäämään (kuten talviaikaiset suojapaikat), voidaan kunnostuksella saada näkyviä tuloksia. On ilmeistä, että kunnostustoimien tulisi olla nykyistä kattavampia ja paremmin suunnattuja rajoittaviin tekijöihin, jotta tulokset näkyisivät.

Amongst the diversity of taxa that occur in the Neotropics, 200 migratory bird species that breed in temperate North America can be found. Many of these populations have seen significant declines since the 1960s. The Wood Thrush, Hylocichla mustelina, is one such species. Shade coffee and other agroforestry practices show potential for benefiting migratory species, but the quality of coffee habitat and optimal habitat characteristics for Wood Thrushes remain unknown. I surveyed a spatially complex, agricultural landscape in Honduras outside the recognized winter range of the Wood Thrush and radio-tagged 46 individuals within rustic coffee farms during the winters of 2012 and 2013. I used telemetry data to calculate metrics of habitat quality based on survival and persistence while also collecting detailed vegetation measurements across the landscape and within each home-range. Mixed-effects models were used to explore the relationship of survival, transience, movement, and home-range size to habitat class and microhabitat variables. Estimates for all four habitat quality metrics fell within the range of previous studies and were significantly related to habitat attributes. Structure, edge habitat, and shade coffee played a key role determining habitat quality. The variables associated with higher habitat quality in this study suggest that rustic coffee farms have potential to support wintering wood thrush populations. However, estimates of survival may be overly optimistic in the presence of transients, transforming highly fragmented landscapes into winter sinks. This study highlights several gaps in current scientific knowledge about some of the most essential questions of Wood Thrush winter ecology.