Migratory swans individually adjust their autumn migration and winter range to a warming climate.

In response to climate warming, migratory animals can alter their migration so that different events in the annual cycle are better aligned in space and time with suitable environmental conditions. Although such responses have been studied extensively during spring migration and the breeding season, much less is known about the influence of temperature on movements throughout autumn migration and how those movements result in a winter range and shifts therein. We use multi-year GPS tracking data to quantify how daily autumn movement and annual winter distance from the breeding grounds are related to temperature in the Western Palearctic Bewick's swan, a long-lived migratory waterbird whose winter range has shifted more than 350 km closer to the breeding grounds since 1970 due to individuals increasingly 'short-stopping' their autumn migration. We show that the migratory movement of swans is driven by lower temperatures throughout the autumn season, with individuals during late autumn moving only substantially when temperatures drop below freezing. As a result, there is large flexibility in their annual winter distance as a response to winter temperature. On average, individuals overwinter 118 km closer to the breeding grounds per 1°C increase in mean December-January temperature. Given the observed temperature increase in the Bewick's swan winter range during the last decades, our results imply that the observed range shift is for a substantial part driven by individual responses to a warming climate. We thus present an example of individual flexibility towards climatic conditions driving the range shift of a migratory species. Our study adds to the understanding of the processes that shape autumn migration decisions, winter ranges and shifts therein, which is crucial to be able to predict how climate change may impact these processes in the future.

Exploring the recovery of a large wetland using black-necked swan blood parameters and body condition 16 years after a pollution-induced disturbance.

Resilience theory has taken center stage in tackling the challenge of wetland recovery on a fast-changing planet. Because of waterbirds' enormous dependence on wetlands, their numbers have long been used as surrogates for wetland recovery over time. However, immigration of individuals can mask actual recoveries at a given wetland. One alternative to expanding the knowledge of wetland recovery is the use of physiological parameters from aquatic organism populations. We explored the variations in the physiological parameters of black-necked swan (BNS) before, during, and after a 16-year period of a pollution-induced disturbance that originated in a pulp-mill wastewater discharge. This disturbance triggered the precipitation of iron (Fe) in the water column of the Río Cruces Wetland in southern Chile, one of the main sites for the global population of BNS Cygnus melancoryphus. We compared our recent (2019) original data (body mass index [BMI], hematocrit, hemoglobin, mean corpuscular volume, blood enzymes, and metabolites) with available datasets from the site obtained before the pollution-induced disturbance (2003) and immediately after the disturbance (2004). Results indicate that, 16 years after the pollution-induced disturbance, some important parameters of animal physiology did not return to their pre-disturbance state. For instance, BMI, triglycerides, and glucose were significantly higher in 2019 than in 2004, right after the disturbance. By contrast, the hemoglobin concentration was significantly lower in 2019 than in 2003 and 2004, and uric acid was 42% higher in 2019 than in 2004. Our results demonstrate that, despite higher BNS numbers with larger body weights present in 2019, the Río Cruces wetland has only partially recovered. We suggest that the impact of megadrought and wetland disappearance far from the site results in high rate of swan immigration, casting uncertainty about using the number of swans alone as honest indicators of wetland recovery after a pollution disturbance. Integr Environ Assess Manag 2023;19:663-675. © 2023 SETAC.

Habitat-, age-, and sex-related alterations in oxidative stress biomarkers in the blood of mute swans (Cygnus olor) inhabiting pomeranian coastal areas (Northern Poland).

The mute swan (Cygnus olor) can be considered a representative species of birds associated with the aquatic environment and responding very clearly to changes in the environment. Assuming that the condition of the mute swan population well reflects the state of the environment, this species was used in our research as a bioindicative species. Thus, the aim of our study was to elucidate the association between metal contents in soil samples collected from a habitat of mute swans and element contents in their feathers as well as the levels of biomarkers of lipid peroxidation, oxidatively modified proteins, and total antioxidant capacity in the blood of mute swans living in three agglomerations in coastal areas in the southern part of the Baltic Sea (Pomeranian region, northern Poland). We compared the effects of inhabitation, age, and sex on the ecophysiological accumulation of metals in three wintering populations of the mute swan from coastal areas of northern Poland, i.e., Slupsk, Gdynia, and Sopot. In Slupsk, the anthropogenic pressure was related predominantly to the level of Al and, to a lesser extent, to the content of Rh and Ru. We found maximum levels of lipid peroxidation biomarkers in the blood of the mute swans from Gdynia (38.20 ± 6.35 nmol MDA·mL-1). At the same time, maximum levels of aldehydic and ketonic derivatives of oxidatively modified proteins were noted in the blood of swans from Sopot compared to the values obtained in mute swans from Slupsk and Gdynia. This trend suggesting high levels of oxidative stress biomarkers was also confirmed by a decrease in the total antioxidant capacity in these groups.

Emergence, prevalence, and evolution of H5N8 avian influenza viruses in central China, 2020.

Highly pathogenic influenza A(H5N8) viruses have caused several worldwide outbreaks in birds and are able cross the species barrier to infect humans, posing a substantial threat to public health. After the first detection of H5N8 viruses in deceased swans in Inner Mongolia, we performed early warning and active monitoring along swan migration routes in central China. We isolated and sequenced 42 avian influenza viruses, including 40 H5N8 viruses, 1 H5N2 virus, and 1 H9N2 virus, in central China. Our H5N8 viruses isolated in swan stopover sites and wintering grounds showed high nucleotide homologies in the whole genome, revealing a common evolutionary source. Phylogenetic analysis revealed that the H5 viruses of clade 2.3.4.4b prevalent in 2020 have further diverged into two sub-clades: b1 and b2. The phylogeographic analysis also showed that the viruses of sub-clade b2 most likely originated from poultry in Russia. Notably, whooper swans were found to be responsible for the introduction of sub-clade b2 viruses in central China; whooper and tundra swans play a role in viral spread in the Yellow River Basin and the Yangtze River Basin, respectively. Our findings highlight swans as an indicator species for transborder spreading and monitoring of the H5N8 virus.

Function of the waterfowl nests as reproduction and living areas for leeches (Annelida: Hirudinea).

Some species of leeches migrate into waterfowl nests and use these both as general habitats and to deposit cocoons, but ecological associations between leeches and birds are not well understood. In the present study, characteristics of waterfowl nests both as living area for leeches (Hirudinea) and as reproduction areas for select hirudinid leeches (Hirudo verbana and Haemopis sanguisuga) was investigated in both natural and controlled laboratory conditions. A total of 48 leeches were detected in 23 of the 51 nests surveyed in natural habitats. The leeches were detected more frequently but there were less dense populations in the nests of the great crested grebe (Podiceps cristatus) (frequency: 57 %, population density: 0.71 ± 0.76 leeches/nest), and leeches were detected less frequently but there were more dense populations in the nests of coots (Fulica atra) (frequency: 36 %, population density: 0.91 ± 1.70 leeches/nest). Although the hirudinid leeches naturally reproduce between June and September, cocoons were only detected in August and September, when the nests were not actively used by the waterfowl and when water depths were less. In laboratory conditions, gravid medicinal leeches prefer moist peat rather than waterfowl nests for cocoon deposition. Results from the present study indicate leeches more frequently use the nests of coots, which have both dry and wet layers, compared to the nests of the great crested grebe, which have only a wet layer. Leeches were also found to be more prevalent in bird nests during spring months, during the reproductive periods of the waterfowl.

Extrinsic factors, endocrine mechanisms, and behavioral indicators of migratory restlessness in wintering whooper swans (Cygnus cygnus).

Extrinsic factors, endocrine mechanisms, and behavioral indicators of migratory restlessness were studied in wintering whooper swans (Cygnus cygnus) in the Sanmenxia Swan National Wetland Park in western Henan Province, central China. First, the fecal glucocorticoid metabolite (FGM) concentration was established and related to mean air temperature or photo period (day length) using simple linear or non-linear regression models. After a model selection procedure, the best fitted model revealed that an increase of FGM concentration was associated with an increase in the squared mean air temperature (R2 = 0.88). Other models showed an increasing FGM concentration to correspond with increasing values of day length, squared day length, and mean air temperature-however without statistical support. In a second step, behavioral frequencies of seven behaviors were condensed into three behavioral principal components (PCs) using principal components analysis. Behavioral PCs largely corresponded to three activity phases described for wintering whooper swans in central China and were correlated with the FGM concentration using Spearman's rank-order correlations. Results revealed a significant correlation between FGM and behavioral PC2 (positive factor loadings from vigilance and preening, negative loading from foraging). Finally, we tested for an effect of behavioral PCs on changes in winter home range size using a set of multiple linear regression models. Results of averaged model parameter estimates showed only the behavioral PC3 (positive factor loadings from fighting and calling, negative loading from locomotion) had a marginal significant effect on home range size. Results confirmed findings of previous studies on migratory restlessness in whooper swans. However, due to the small sample size (N = 15 weeks) the effect of PC3 on home range size was weak and should be viewed with caution.

Trematode diversity in freshwater snails from a stopover point for migratory waterfowls in Hokkaido, Japan: An assessment by molecular phylogenetic and population genetic analyses.

The cryptic diversity of trematodes was evaluated in the Nagayama-Shinkawa River, an artificial canal of the Ishikari River System of Hokkaido, Japan. Numerous migratory waterfowls use the canal as a stopover point in every spring season. The lymnaeid snail, Radix auricularia, and the semisulcospirid snail, Semisulcospira libertina, colonize the static and flowing water areas, respectively. The trematode fauna of the two snails was assessed by molecular phylogenetic and population genetic analyses. Each of distinctive clades in mitochondrial DNA trees was arbitrarily set as a species. In total, 14 species of the families Diplostomidae, Echinostomatidae, Notocotylidae, Plagiorchiidae, and Strigeidae occurred in R. auricularia, wherease S. libertina harbored 10 species of the families Echinochasmidae, Heterophyidae, Notocotylidae, and Lecithodendridae and Cercaria creta, an unclassified species whose adult stage is still unknown. The species diversity of the larval trematodes could be recognized as a "hot spot", suggesting that the seasonal visit of waterfowls is very important to spread trematodes and to keep their diversity. A high intraspecific genetic diversity was observed in the echinostomatid, notocotylid, echinochasmid, and heterophyid species, whose definitive hosts include birds. It seems likely that each of the parasite populations is always disturbed by repeated visits of waterfowls.

Association of wild bird densities around poultry farms with the risk of highly pathogenic avian influenza virus subtype H5N8 outbreaks in the Netherlands, 2016.

Highly pathogenic (HP) avian influenza viruses (AIV) can spread globally through migratory birds and cause massive outbreaks in commercial poultry. AIV outbreaks have been associated with proximity to waterbodies, presence of waterfowl or wild bird cases near poultry farms. In this study, we compared densities of selected HPAI high-risk wild bird species around 7 locations (H farms) infected with HPAIV H5N8 in the Netherlands in 2016-2017 to densities around 21 non-infected reference farms. Nine reference farms were in low-lying water-rich areas (R-W) and 12 in higher non-water-rich areas (R-NW). Average monthly numbers/km2 of Eurasian wigeons, tufted ducks, Anatidae (ducks, geese and swans) and Laridae (gulls) were calculated between September and April in rings of 0-1, 1-3, 3-6 and 6-10 km around the farms. Linear mixed model analyses showed generally higher bird densities for H and R-W compared to R-NW farms between October and March. This was most striking for Eurasian wigeons, with in peak month December 105 (95% CI:17-642) and 40 (7-214) times higher densities around H and R-W farms, respectively, compared to R-NW farms. Increased densities around H farms for Eurasian wigeons and Anatidae were more pronounced for distances up to 10 km compared to 0-1 km that mostly consists of the farm yard, which is an unattractive habitat for waterfowl. This distance effect was not observed in gulls, nor in tufted ducks that live on large open waterbodies which are unlikely to be within 0-1 km of farms. This study provides insights into spatio-temporal density dynamics of HPAI high-risk birds around farms and their associations with poultry outbreaks. The outcomes indicate that knowledge of environmental and ecological drivers for wild bird presence and abundance may facilitate identification of priority areas for surveillance and biosecurity measures and decisions on establishments of poultry farms to reduce risk of HPAI outbreaks.

Effectiveness of the European Natura 2000 network to sustain a specialist wintering waterbird population in the face of climate change.

Analysis of coordinated Greater Scaup (Aythya marila) count data from the last 30 years showed a 38.1% decrease in wintering numbers in North-West Europe, from 309,000 during 1988-1991 to c.192,300 individuals during 2015-2018. Annual trends in wintering numbers differed throughout the range. Numbers decreased in the UK, Ireland, and in the Netherlands, while numbers were stable in Denmark. Germany, Poland, Sweden, and Estonia showed increasing numbers, suggesting a shift in the distribution of the species within its wintering grounds towards the east and north. Higher temperatures in northern and eastern areas were correlated with the range shift of the wintering distribution. Deaths from bycatch drowning of Scaup in fishing gear have significantly decreased in recent decades in the Netherlands, where currently the greatest threat is considered the deterioration of food resources. The increasing concentration of wintering Scaup in coastal Poland and Germany (where lack of effective implementation of conservation measures fail to protect the species from the impacts of bycatch and declining food quality) pose major threats to the entire population.

Active immunization against AMH reveals its inhibitory role in the development of pre-ovulatory follicles in Zhedong White geese.

The aim of this study was to investigate the effects of active immunization against recombinant Anti-Müllerian hormone (AMH) protein on the ovarian follicular development, egg production, and molecular regulatory mechanisms in broody-prone Zhedong White geese. For this, a recombinant goose AMH protein was expressed using a prokaryotic expression system. Fifty incubating geese from the same genetic background were selected and equally divided into two groups. The immunization group was actively immunized against the recombinant goose AMH protein, whereas the control group was immunized against bovine serum albumin (BSA). Immunization against AMH accelerated ovarian follicular development and increased clutch sizes by one to two eggs in two consecutive laying-incubation cycles. Furthermore, immunization against AMH upregulated the mRNA transcription levels of the FSH-beta gene in the pituitary gland, and FSHR, 3beta-HSD, and Smad4 genes in the granulosa layer of pre-ovulatory follicles; however, immunization downregulated the expression of the OCLN gene in the granulosa layer of pre-ovulatory follicles, and Smad5 and Smad9 genes in the granulosa layer of SYFs. These results suggest that AMH might hinder ovarian follicular development by decreasing both pituitary FSH secretion as well as ovarian follicular sensitivity to FSH. The latter molecular mechanism could be fulfilled by regulating Smad5 or Smad9 signals in SYFs, as well as the FSHR and Smad4 signals that affect progesterone synthesis and yolk deposition in the pre-ovulatory follicles.

Migration Patterns and Characteristics of Eurasian Wigeons (Mareca penelope) Wintering in Southwestern Japan Based on Satellite Tracking.

Understanding migration ecology of Eurasian wigeons (Mareca penelope) is crucial for effective population management, mitigating conflicts with human, and habitat conservation. The objectives of the present study were 1) to determine their migration patterns of Eurasian wigeons in the East Asian flyway, and 2) to identify the key breeding and stopover sites. From 2007 to 2016, a total of the 64 wigeons, which wintered in Japan, were equipped with satellite transmitters. Most Eurasian wigeons migrated to breeding sites in Russia either (a) via a continental route through China, (b) via the Kamchatka Peninsula, or (c) via Sakhalin Island. In spring, many of the Eurasian wigeons (60.98%) migrated via the continental route. In autumn, most Eurasian wigeons (57.14%) migrated through Kamchatka. These differences may be attributable to the influence of Okhotsk Sea air mass on migration decisions due to loop migration. Similarly to the migration of Mallards, Eurasian wigeons employed a "long-stay and short-travel" migration strategy. Eurasian wigeons mainly nested between latitude between 43° to 75°N. From the present findings and the published literature, Eurasian wigeons that winter in Japan are considered to migrate to Russia, China, and the United States during the breeding season, although the main breeding area is in northeastern Russia. A total of 296 important sites to Eurasian wigeons were mapped, and 118 location names with geographic coordinates, and the top five most frequently used sites were identified in each season.

Dietary habits of the black-necked swan Cygnus melancoryphus (Birds: Anatidae) and variability of the aquatic macrophyte cover in the Río Cruces wetland, southern Chile.

The black-necked swan Cygnus melancoryphus is an aquatic herbivorous bird whose dietary habits depend on the dominance and accessibility of macrophyte banks in shallow areas of coastal and limnetic wetlands in southern South America. The swans from the Río Cruces wetland in southern Chile (ca. 39°S) feed mainly on the macrophyte Egeria densa from the water column between depths from less than 0,5 and 2,0 m. A micro- histological analysis of black-necked swan feces (N = 152) collected during six sampling occasions between 2012 and 2017 confirms the preferred consumption of E. densa and highlights the impact of temporal changes in the cover of these macrophytes on the swan's diet. The dietary composition of black-necked swans appears as a reliable proxy for temporal changes in the distribution of the most common aquatic macrophytes in the Río Cruces wetland. These results highlight the importance of preserving shallow wetlands as the habitat for aquatic macrophytes that provide the main food source for these herbivorous water birds.

Day and night use of habitats by northern pintails during winter in a primary rice-growing region of Iberia.

Loss of natural wetlands is a global phenomenon that has severe consequences for waterbird populations and their associated ecosystem services. Although agroecosystems can reduce the impact of natural habitat loss, drivers of use of such artificial habitats by waterbirds remain poorly understood. Using the cosmopolitan northern pintail Anas acuta as a model species, we monitored home-range and fine-scale resource selection across the agricultural landscape. Individuals were tracked using GPS-GSM transmitters, and a suite of environmental and landscape features were measured throughout the winter seasons. Spatial patterns of habitat use were analysed using generalized linear mixed effect models by integrating field-observations with GPS telemetry. All birds used rice fields as foraging grounds at night and commuted to an adjacent reservoir to roost during daylight. Home-ranges and maximum foraging distances of nocturnally foraging birds increased with decreasing availability of flooded fields, and were positively correlated with moonlight levels. Birds selected flooded rice paddies (water depth range: 9-21 cm) with standing stubble and substrate with pebbles smaller than 0.5 cm in diameter. Density of rice seeds, rice paddy size, and other environmental and landscape features did not emerge as significant predictors. Our findings indicate that nocturnal foraging of northern pintails within rice fields is driven primarily by straw manipulation, water level and substrate pebble size. Thus, the presence of standing stubble in flooded paddies with soft bottoms should be prioritized to improve foraging areas for dabbling ducks. These management procedures in themselves would not increase economic costs or affect rice production and could be applied for dabbling-duck conservation throughout the world.

Effect of incubation temperature on sex-dependent embryo mortality and morphological traits in Mallard.

Although birds have genetically determined sex, the sex ratio has been reported to deviate from parity in several studies. Temperature-dependent sex determination, which is common in reptiles, is absent in birds. However, females are able to adjust their investment into eggs according to the sex of the embryo, which may cause sex-specific embryonic mortality. Incubation temperature may also cause sex-biased embryonic mortality, and it may differentially affect the phenotype of male and female hatchlings. We aimed to investigate differences between male and female Mallard embryos regarding their egg size, mortality during incubation and hatchling phenotype in relation to incubation temperature. Mallard eggs were incubated under six constant incubation temperatures (ranging from 35.0 to 38.0 °C). Hatchlings were weighed, and their morphological traits were measured. We determined the sex of hatchlings and unhatched embryos by genetic analysis and found higher male embryonic mortality at 35.5 °C (44 males vs. 28 females) and a higher proportion of female hatchlings at 38 °C (24 males vs. 38 females); however, these results were not statistically significant. Our results suggest that Mallard females do not differentiate quantitatively between sexes during egg production. Male hatchlings were significantly larger but not heavier than females. The size difference between sexes was most pronounced at temperatures around 36 °C, which is the mean temperature of naturally incubated Mallard eggs.

New evidence for the east-west spread of the highly pathogenic avian influenza H5N1 virus between Central Asian and east Asian-Australasian flyways in China.

The spread of highly pathogenic avian influenza (HPAI) H5N1 virus is associated with wild fowl migration in East Asian-Australasian (EA) and Central Asian (CA) flyways. However, the spread of H5N1 virus between the two flyways is still unclear. Here, the movements of wild waterfowl were obtained from satellite tracking data covering seven bar-headed geese and three great black-headed gulls breeding in the Qinghai Lake area (along the EA flyway), and 20 whooper swans wintering in the Sanmenxia Reservoir area (at the CA flyway). From the 2688 samples that were screened from wild birds at Qinghai Lake after an outbreak of H5N1 in July 2015, four genomes of H5N1 virus were obtained from bar-headed geese. The results of phylogenetic analysis indicated that these H5N1 viruses belonged to clade 2.3.2.1c and their gene fragments were highly homologous with A/whooper swan/Henan/SMX1/2015 (H5N1) virus (ranging from 99.76% to 100.00%) isolated from a dead whooper swan from the Sanmenxia Reservoir area along the EA flyway in January 2015. Furthermore, the coincidental timing of the H5N1 outbreak with spring migration, together with phylogenetic evidence, provided new evidence of the east-to-west spread of HPAI H5N1 between the EA and CA migratory flyways of China.

Assessing mineral status in edible tissues of domestic and game animals: a review with a special emphasis in tropical regions.

Mineral status in edible tissues has been extensively studied since the beginning of the twentieth century. Most research focus on nutrition, as the earliest reports were essentially related to nutrition, animal health and mineral deficiencies. Nutrition wise, minerals are of great importance for consumers worldwide, as meat (i.e. beef, pork, chicken) and fish are major sources of protein in human diets. Nutrition gains renewed importance in the tropical context, since tropical forages are poor in minerals. This fact contributes to mineral deficiencies and impaired production performance in extensive production systems, with greater emphasis in ruminant species. In addition to nutrition, several other factors have an important impact in mineral metabolism such as geographic location, gender and species. In this article, we aim to infer on both the role in the organism and the amount present in various edible tissues of different species, either game or production animals, presenting an overall perspective in the context of tropical animal production.

A potential role for SMAD9 in goose follicular selection through regulation of mRNA levels of luteinizing hormone receptor.

The egg production of poultry depends on follicular development and selection. Nonetheless, the mechanism underlying the priority of selecting of hierarchical follicles is completely unknown. SMAD9 is one of the important transcription factors in the BMP/SMAD pathway and is involved in goose follicular initiation. To identify its potential role in determination of the goose follicle hierarchy, we used BMP type I receptor inhibitor LDN-193189 both in vivo and in vitro and found that SMAD9 mRNA expression decreased in the presence of LDN-193189. While the level of SMAD9 mRNA decreased after treatment with LDN-193189, we found that the egg production (7.08 eggs per bird per year) of the animals increased, estradiol (E2) levels significantly increased, but the levels of progesterone (P4) remained unchanged. We also detected a significant increase in luteinizing hormone receptor (LHR) mRNA expression, but no change in follicle-stimulating hormone receptor (FSHR) mRNA amounts. The in vitro experimental results indicated that SMAD9 knockdown by RNA interference noticeably reduced E2 and P4 biosynthesis and FSHR and LHR mRNA expression in goose granulosa cells. Chromatin immunoprecipitation assay of goose granulosa cells revealed that phospho-SMAD9 bound to the LHR promoter and possibly regulated its transcriptional activity. These findings revealed that SMAD9 is differentially expressed in goose follicles, and acts as a key player in the control over goose follicular selection.

Endocrine and molecular regulation mechanisms of the reproductive system of Hungarian White geese investigated under two artificial photoperiodic programs.

Hungarian White geese are regarded as good producers of meat, eggs, and feathers, but specific lighting schedules are required to improve their egg-laying performance. This study reveals the neuroendocrine regulatory mechanisms that govern the reproductive activities and egg-laying performances of Hungarian White geese. The results indicated that increasing the daily photoperiod from a short 8 h period to either 11 h or 14 h initiated reproduction. Egg-laying rates increased faster in the 14 h group, peaking (48.2%) on day 33 as compared to the peak (52.67%) reached on day 53 in the 11 h group. Changes to the plasma estradiol and progesterone concentrations produced similar patterns in the two groups. In the hypothalamus, OPN5, Dio2, c-Fos, and GnRH-I expression levels showed similar sequential increases and decreases. Changes in GnIH and VIP expression levels were the opposite to those of GnRH-I, but the levels peaked earlier under the 14 h photoperiod conditions. Pituitary LH beta and FSH beta expression levels increased at slower rates but remained significantly higher in the 11 h group than in the 14 h group. However, pituitary PRL expression increased considerably earlier and was higher in 14 h geese than in 11 h geese, which was opposite to the observed egg-laying rate patterns. An increase from a short to a relatively long photoperiod (11 h) regulated the neuroendocrine system and led to reproductive activities being sustained for a longer period, which resulted in high egg-laying performances.

Waterbird response to variable-timing of drawdown in rice fields after winter-flooding.

Wetland loss and degradation have been extensive across the world, especially in California's Central Valley where over 90% of the natural wetlands have been converted to agricultural and urban uses. In the Central Valley today, a much smaller network of managed wetlands and flooded agricultural fields supports almost five million waterfowl and half a million shorebirds. Over 50% of waterbird habitat in the Central Valley is provided by flooded agricultural land, primarily rice (Oryza sativa). Each year non-breeding waterbird habitat decreases in the late winter as flooded agricultural fields are drained after waterfowl hunting season in late-January to prepare for the next crop. This study evaluated a practice called 'variable drawdown' that involves delaying the removal of water from rice fields by 1, 2, and 3 weeks to extend the availability of flooded habitat later into February and March. We studied waterbird response to variable drawdown in 2012 and 2013 at twenty rice farms throughout the northern half of the Central Valley. The staggered drawdown created a mosaic of water depths throughout the six-week study period. The 3-week delay in drawdown supported more dabbling ducks than earlier drawdowns in the first half of the study and more shorebirds and long-legged wading birds during the second half of the study. The timing of highest use of each drawdown treatment differed for each waterbird guild; dabbling ducks, geese and swans benefited at the beginning, then long-legged wading birds, followed by shorebirds. Despite the presence of appropriate water depths for shorebirds across the treatments during the entire study period, shorebird densities were highest near the end of the study when the 3-week-delayed drawdown was providing the majority of the habitat on the landscape. This suggests that shorebirds may have concentrated in our study fields due to decreasing availability of shallow water habitat elsewhere. The practice of variable drawdown successfully extended the availability of waterbird habitat provided by post-harvest flooded rice fields later into winter.

Incubation temperature influences the behavioral traits of a young precocial bird.

The environment in which animals develop can have important consequences for their phenotype. In reptiles, incubation temperature is a critical aspect of the early developmental environment. Incubation temperature influences morphology, physiology, and behavior of non-avian reptiles, however, little is known about how incubation temperature influences offspring phenotype and behaviors important to avian survival. To investigate whether incubation temperature influences avian behaviors, we collected wood duck (Aix sponsa) eggs from the field and incubated them at three naturally occurring incubation temperatures (35.0, 35.8, and 37.0°C). We conducted multiple repeated behavioral trials on individual ducklings between 5 and 15 days post-hatch to assess activity, exploratory, and boldness behaviors, classified along a proactive-reactive continuum. We measured growth rates and circulating levels of baseline and stress-induced corticosterone levels to investigate possible physiological correlates of behavior. Ducklings incubated at the lowest temperature displayed more proactive behaviors than those incubated at the two higher temperatures. We also found that younger ducklings exhibited more proactive behavior than older ducklings and males exhibited more proactive behavior than females. Further, duckling behaviors were repeatable across time and contexts, indicative of a proactive-reactive continuum of behavioral tendencies. However, neither corticosterone levels nor growth rates were related to behavior. This provides some of the first evidence that incubation temperature, a critical parental effect, influences avian offspring behaviors that may be important for survival. Our results identify incubation temperature as a mechanism that contributes to the development of behavioral traits and, in part, explains how multiple behavioral types may be maintained within populations.