Influence Nest Survival Research Articles

Factors Affecting Survival of Common Sandpiper (Actitis hypoleucos) Nests along the Semi-Natural Vistula River in Poland.

Predation is an important factor limiting bird populations and is usually the main factor influencing nest survival. In riverine habitats, flooding poses an additional significant challenge. Our study aimed to elucidate the influence of nest location and incubation timing on the survival of common sandpiper nests in a large, semi-natural, lowland river. The survey was carried out in central Poland on the Vistula River, in 2014-2015, 2021, and 2023, along two river sections 2 km and 10 km in length. The nest survival rate was 27%, which is twice as low as that reported on small upland rivers, with flooding being an additional factor causing losses on the Vistula River. Our research showed that mammalian and avian predation accounted for 51% of losses and flooding for 49% of losses. The negative impact of floods on nest survival decreased as the breeding season progressed between May and July, while the chances of being depredated increased during the same period. Nests placed under shrubs were less likely predated than nests located in grass. Moreover, locating the nest in proximity to water increased nesting survival and in fact, more nests found in our study were situated close to the water's edge.

Saffron-cowled Blackbirds’ reduced nest success in Argentina’s agricultural land highlights the importance of non-agricultural habitat for its conservation

Abstract The Saffron-cowled Blackbird (Xanthopsar flavus) is a globally endangered icterid endemic to the southern South American grasslands. Temperate grasslands are among the most threatened ecosystems in South America due to their high rate of land use change. In northeastern Argentina, over the last century, the conversion of natural grasslands to livestock farming, croplands, and afforestation has resulted in significant losses of breeding habitat for the Saffron-cowled Blackbird. Consequently, it has suffered severe populational declines, and its remaining populations are fragmented. In order to understand the impact of agricultural systems on the Saffron-cowled Blackbird populations, we studied its breeding biology (clutch size, hatching success, nestling production, and fledgling success) and the main parameters that influence nest survival rate in five breeding habitat types. During the breeding seasons of 2015 to 2019, we located nests and monitored their fate. We found that the cumulative probability of nest survival over the entire nesting cycle (i.e. laying, incubation, and chick rearing) was 0.06, and was lower for nests situated in grazed land covers. Conversely, nest survival was greater in breeding sites without agricultural use, particularly in marshes. Predation was the main cause of nest failure (76%), followed by brood parasitism (10%), and trampling by cattle and agricultural machinery (6%). Brood parasitism rates were higher in grazed paddocks, contributing together with predation to the failure of nests in this habitat. Our findings indicate a negative impact of livestock ranching on Saffron-cowled Blackbird reproduction. Non-agriculture habitats, such as wetlands and flooded areas, are important as refuges for nesting. Thus, the creation of breeding refuges (non-productive sites) within agricultural matrices, in association with biodiversity-friendly agricultural practices, is crucial to ensure the Saffron-cowled Blackbird’s maintenance.

Response of greater sage‐grouse to sagebrush reduction treatments in Wyoming big sagebrush

AbstractVegetation treatments have been widely implemented in efforts to enhance conditions for wildlife populations. Yet the effectiveness of such efforts often lack rigorous evaluations to determine whether these practices are effective for targeted species. This is particularly important when manipulating wildlife habitats in ecosystems that are faced with multiple stressors. The sagebrush (Artemisiaspp.) ecosystem has been altered extensively over the last century leading to declines of many associated species. Wyoming big sagebrush (A. tridentata wyomingensis) is the most widely distributed subspecies, providing important habitats for sagebrush‐obligate and associated wildlife. Sagebrush often has been treated with chemicals, mechanical treatments, and prescribed burning to increase herbaceous forage species released from competition with sagebrush overstory. Despite many studies documenting negative effects of sagebrush control on greater sage‐grouse (Centrocercus urophasianus) habitat, treatments are still proposed as a means of improving habitat for sage‐grouse and other sagebrush‐dependent species. Furthermore, most studies have focused on vegetation response and none have rigorously evaluated the direct influence of these treatments on sage‐grouse. We initiated a 9‐year (2011–2019) experimental study in central Wyoming, USA, to better understand how greater sage‐grouse respond to sagebrush reduction treatments in Wyoming big sagebrush communities. We evaluated the influence of 2 common sagebrush treatments on greater sage‐grouse demography and resource selection. We implemented mowing and tebuthiuron application in winter and spring 2014 and evaluated the pre‐ (2011–2013) and post‐treatment (2014–2019) responses of sage‐grouse relative to these management actions. We evaluated responses to treatments using demographic and behavioral data collected from 620 radio‐marked female greater sage‐grouse. Our specific objectives were to evaluate how treatments influenced 1) sage‐grouse reproductive success and female survival; 2) sage‐grouse nesting, brood‐rearing, and female resource selection; 3) vegetation responses; and 4) forbs and invertebrates. Our results generally suggested neutral demographic responses and slight avoidance by greater sage‐grouse in response to Wyoming big sagebrush treated by mowing and tebuthiuron. Neither mowing nor tebuthiuron treatments influenced nest survival, brood survival, or female survival. Selection for nest and brood‐rearing sites did not differ before and after treatments. Females selected habitats near treatments before and after they were implemented; however, the strength of selection was lower after treatments compared with pre‐treatment periods, which may be explained by a lack of response in vegetation and invertebrates following treatments. Perennial grass cover and height varied temporally yet did not vary systematically between treatment and control plots. Forb cover and species richness varied annually but not in relation to either treatment type. Perennial grass cover and height, forb cover, and forb species richness did not increase within mowed or tebuthiuron‐treated areas that received 2 or 6 years of grazing rest compared with areas that received no grazing rest. Finally, forb and invertebrate dry mass did not differ between treated plots and control plots at mowing or tebuthiuron sites in any years following treatments. Results from our study add to a large body of evidence that sage‐grouse using Wyoming big sagebrush vegetation communities do not respond positively to sagebrush manipulation treatments. Management practices that focus on the maintenance of large, undisturbed tracts of sagebrush will best facilitate the persistence of sage‐grouse populations and other species reliant on the sagebrush steppe.

Nest‐site features influence nest survival of the Hellmayr's pipit in extensive cattle‐grazed grasslands

AbstractThe Pampas Grasslands in South America have been almost completely transformed by urbanization and agriculture. Many grassland birds persist only in extensive natural pasturelands, which are under constant pressure from fragmentation, cattle‐grazing, and exotic plant species. Identifying which habitat features affect bird breeding success is important for their conservation in altered habitats, although few studies have been conducted in the Pampas Grasslands. We analyzed the influence of habitat features on the daily nest survival rates (DSR) of the Hellmayr's pipit (Anthus hellmayri), a grassland passerine endemic to South America, in a cattle‐grazed grassland. We evaluated the effects of vegetation features at a nest‐site scale, proximity to habitat edges, cattle density, and temporal factors. During 3 breeding seasons (2017–2020), we confirmed the fate of 90 nests, 25 of which were successful (27.8%). Predation was the most common cause of failure (80%), followed by weather‐induced abandonment (10.8%). Average DSR was 0.9106, with a cumulative survival probability of only 7.4%. The best model indicated that DSR was higher in nests adjacent to grass clumps than in those placed in depressions and followed a quadratic trend with nest age. Clump nests may be better protected from aerial predators and rainfall; hence pipits could be more successful in areas with more grass clumps. The very low nest success raises concern regarding the value of these grazing fields as breeding habitats; we urge authorities and landowners to increase conservation efforts in the remaining natural grasslands in the Pampas.

Nest traits and major flooding events influence nest survival of Emperor Geese while regional environmental variation linked to climate does not

Abstract The reproductive ecology of geese that breed in the Arctic and subarctic is likely susceptible to the effects of climate change, which is projected to alter the environmental conditions of northern latitudes. Nest survival is an important component of productivity in geese; however, the effects of regional environmental conditions on nest survival are not well understood for some species, including the Emperor Goose (Anser canagicus), a species of conservation concern that is endemic to the Bering Sea region. We estimated nest survival and examined how indices of regional environmental conditions, nest traits (nest age, initiation date, and maximum number of eggs in the nest), and researcher disturbance influenced daily survival probability (DSP) of Emperor Goose nests using hierarchical models and 24 years of nest monitoring data (1994–2017) from the Yukon–Kuskokwim Delta (Y–K Delta) in western Alaska. Our results indicate that overall nest survival was generally high (µ = 0.766, 95% CRI: 0.655–0.849) and ranged from 0.327 (95% CRI: 0.176–0.482) in 2013 to 0.905 (95% CRI: 0.839–0.953) in 1995. We found that DSPs of nests were influenced by nest traits, negatively influenced by major tidal flooding events and by researcher disturbance, but were not influenced by regional indices of spring timing, temperature and precipitation during nesting, or fox and vole abundance on the Y–K Delta. However, the number of nests found each year was negatively related to our index of fox abundance, suggesting nests that failed as a result of fox predation may have never been discovered due to our limited nest-searching efforts during egg laying. Our results suggest that regional environmental variation had minimal influence on the nest survival of Emperor Geese, although major flooding events were important. Nevertheless, we suspect that within-year variation in local weather conditions and local abundance of predators and alternative prey may be important and should be considered in future studies.

Woody plant encroachment reduces density of most grassland specialists in a desert grassland but has limited influence on nest survival

AbstractWoody plants are proliferating in grassland ecosystems worldwide, altering distributions and demography of many imperiled species. The transition from grassland to shrubland is especially prevalent in semiarid regions, but the influence of woody plant encroachment (WPE) on birds that breed in desert grasslands is poorly understood, which reduces the potential for developing effective conservation actions for this imperiled group. During 2013–2015, we surveyed breeding birds on 140 10-ha plots in southeastern Arizona, USA, that spanned a gradient of encroachment (0–37% cover) by Prosopis (mesquite), which has invaded grasslands worldwide. We evaluated the effect of WPE on density, nest placement, and nest survival at 3 spatial scales (within 1.5 m and 5 m of the nest and at the 10-ha plot) for common species and 3 species groups: obligate grassland specialists (n = 7 species), facultative grassland specialists (n = 17), and species not typically associated with grasslands (n = 42). Density of the obligate species group decreased by 30% across the gradient of shrub (0.5–2 m tall) cover and by 23% across the gradient of tree (>2 m tall) cover. For 3 of 4 obligate species, density decreased by ≥50% when tree cover increased from 0 to 15%. In contrast, density of the facultative species group nearly tripled as tree cover increased from 0 to 22%. Obligate species placed nests 3.5 times farther from trees than facultative species (51.9 vs. 14.8 m). WPE influenced nest survival for 2 species but effects were inconsistent across spatial scales: nest survival of Grasshopper Sparrow (Ammodramus savannarum) decreased with increasing cover of trees on plots and shrubs within 5 m of the nest, and nest survival of Mourning Dove (Zenaida macroura) increased with increasing cover of shrubs on plots. Our results demonstrate that many grassland obligates are affected adversely even by small increases in woody cover. Consequently, restoration efforts should focus on early stages of WPE (i.e., cover <10% and shrubs <2 m tall) when removal of woody plants is more effective and less expensive relative to later stages.

Multi-scale nest survival analysis suggests new cavities improve nest success for the Green-barred Woodpecker, but not the Campo Flicker, in a threatened woodland of Argentina

Abstract Understanding factors affecting nest survival of woodpeckers in threatened landscapes is a key tool for land managers, particularly when conservation depends on public policies. However, information of Neotropical woodpeckers breeding in southern temperate forests is noticeably sparse despite the worrying conservation status of these ecosystems and woodpeckers’ key role as cavity providers. Our objective was to assess the relationship between tree cavity features, vegetation structure, and landscape configuration on the nest survival of the Green-barred Woodpecker (Colaptes melanochloros) and the Campo Flicker (C. campestris). We monitored nests of these woodpeckers during 3 breeding seasons from 2015 to 2018 in a woodland of east-central Argentina threatened by selective tree logging and soil material extraction. We recorded features that presumably influence nest survival at a micro-scale (cavity, cavity-tree features, and foliage cover around the cavity) and a macro-scale (forest cover and shape index within a 500-m circle around the nest). We did not find support for a relationship between daily nest survival rates (DSR) and cavity features, vegetation structure, or landscape configuration. However, new cavities were more successful than reused ones for the Green-barred Woodpecker. We also found a surprisingly high rate (~33% of nest failures) of nest abandonment for both species. Abandonment may be a factor regulating this population and causes of abandonment warrants further investigation. Given the importance of new cavities to the success of Green-barred Woodpeckers, our results indicate the preservation of medium-size trees (20 cm < diameter at breast height [DBH] < 50 cm) with wood softened by degradation processes (preferred by the species to excavate cavities) would facilitate persistence both of this woodpecker and the cavity nesting community. Effective audit of soil material extraction and controlled selective timber logging practices (including preservation of mature trees) in compliance with existing regulations could contribute to this type of habitat maintenance.

Nest survival of the Snowy Plover Charadrius nivosus at Marismas Nacionales, Nayarit

Breeding habitat loss and nest predation are considered the main causes of Snowy Plover (Charadrius nivosus) populations decline worldwide. We evaluated the effects of season, nest age, distance to nearest vegetation patch, distance to nearest body of water, habitat type, and nesting substrate on the daily survival rate of Snowy Plover nests. During 2014-2015, we located 84 nests in Las Garzas-Chahuin-Chihua lagoon in Marismas Nacionales, Nayarit, Mexico. We used MARK software to estimate daily nest survival rate, which was 0.969 (95% CI = 0.95 - 0.97) for both breeding seasons combined, with a 42% finite nesting success. A total of 44 nests (52%) were successful, while 40 (48%) failed. The main causes of nest failure were predation (n = 30; 75% of failed nests) and flooding (n = 9; 22.5% of failed nests); one nest was lost due to unknown causes (2.5%). Daily survival rate increased with nest age and distance from the nearest vegetation patch. By contrast, daily survival rate decreased with the progression of the breeding season; a higher probability of nest success was evident when established early in the breeding season. Our results show the importance of different positive and negative factors influencing nest survival that might be considered as part of conservation strategies.

Reassessing perennial cover as a driver of duck nest survival in the Prairie Pothole Region

AbstractConservation plans designed to sustain North American duck populations prominently feature a key hypothesis stating that the amount of the landscape in perennial cover surrounding upland duck nests positively influences nest survival rates. Recent conflicting research testing this hypothesis creates ambiguity regarding which management actions to pursue and where to prioritize conservation delivery. We compared existing models and new formulations of existing models explaining spatiotemporal variation in nest survival using independent data documenting the fate of >20,000 duck nests within the Drift Prairie, Missouri Coteau, and Prairie Coteau physiographic regions of the United States Prairie Pothole Region during 2002–2018. Our results suggest an inconsistent relationship between perennial cover and survival of upland duck nests, which depended upon physiographic region and current and time‐lagged landscape and environmental conditions. The magnitude and direction of how perennial cover correlated with daily nest survival depended on its dominance as a landcover type. A positive relationship existed when perennial cover was a minor component of landcover in all physiographic regions (<30% of a 10.4‐km2 area) and, in the Drift Prairie and Prairie Coteau, when perennial cover was the dominant landcover type (>60%). A constant or negative relationship was predicted at locations of about 30–60% perennial cover. Additionally, environmental conditions (i.e., density of wetlands and estimated gross primary productivity in the previous year) moderated or enhanced the effect of perennial cover on nest survival, depending on physiographic region. Our finding of inconsistency in the relationship between perennial cover and nest survival contradicts the conservation premise that nest survival universally increases linearly when uplands are converted to perennial cover. Promoting policies and management actions designed to increase perennial cover can be expected to be situationally but not consistently associated with higher survival of upland duck nests.

Landscape composition, climate variability, and their interaction drive waterfowl nest survival in the Canadian Prairies

AbstractFor upland‐nesting ducks that rely on grassland and wetland habitats in landscapes characterized by human alteration and a strongly fluctuating climate, information on how landscape composition interacts with climate is needed to better understand the security of conservation investments and to inform adaptive management in a changing climate. We characterized spatial and temporal variation in a 10‐year study of nest survival of five species of upland‐nesting ducks at study areas across the Canadian Prairie Pothole Region. We assessed factors affecting nest survival across gradients of landscape composition, climate, and duck density. Habitat characteristics influenced nest survival at multiple scales spanning nest‐scale vegetation density to landscape‐scale perennial cover abundance, with the relative magnitude of spatial variation in nest survival greater than that of temporal variation in this study. An interaction between climate and landscape composition suggested that intact landscapes can moderate the effects of interannual variation in climate, reinforcing the importance of habitat conservation in a changing climate. Measured nest survival rates ranged from 4.7% to 40.5% and were high enough to sustain duck populations in only 31% of study areas, barring sustained climatic conditions suitable for elevating other breeding season vital rates, suggesting the need for continued investment in waterfowl conservation.

Hydrology management influences nest survival but not clutch size in Lesser Scaup

Components of reproductive success such as clutch size and nest survival may greatly affect avian population growth rates. Understanding how environmental conditions influence temporal variation in these demographic parameters could thus provide valuable insight into best management practices for species of concern. One such species that could benefit from a better understanding of such processes is Lesser Scaup (<em>Aythya affinis</em>), whose overall abundance in North America has declined since the early 1980s. We used a long-term study (2005–2019) of Lesser Scaup demography at Red Rock Lakes National Wildlife Refuge in southwestern Montana, USA, to examine how the management of wetland conditions influenced within- and across-year temporal variation in clutch size and nest survival. Predicted clutch size varied more across nest initiation dates (6.18–10.05 eggs) within years than it did across years (7.51–8.38 eggs), and none of the covariates we examined were significantly related to clutch size across years. Nest daily survival rates varied substantially across days within breeding seasons (e.g., 2018: 0.38–0.985), and annual mean nest survival varied greatly across years (0.27–0.58). Furthermore, seasonal chronology of managed wetland water levels influenced nest survival such that years when water levels gradually rose to a maximum late in the breeding season, relative to mean nest initiation date, resulted in the highest nest survival. These findings collectively suggest that when flows can be manipulated with water control structures, efforts to manage the chronology of water levels at watershed and local wetland scales could improve nest survival, whereas such management efforts will not likely affect clutch sizes.

Effects of Colony Disturbance on Reproductive Success and Nest Defense Behaviors in Caribbean Roseate Terns

Heterospecific disturbance in seabird colonies can negatively influence reproductive success both through direct effects, such as predation, and through indirect effects, such as increasing parental energy expenditure via defense behaviors. Here, remote nest cameras were used to evaluate the effects of intrusion on early nest survival and predation risk in Roseate Tern (Sterna dougallii) colonies in the U.S. and British Virgin Islands. Effects of colony traits such as colony size on parental nest defense were also investigated to assess individual response to predator presence in colonies. We counted 141 intrusion events at 118 nests and found that frequency of heterospecific disturbance did not influence nest survival, but did have a positive association with predation rate. Disturbance decreased significantly with colony size and % cover, and disturbance increased with nest density, indicating that concealed, isolated nests within large colonies were less likely to be disturbed. Parental nest defense decreased significantly with colony size and nest density. Results were likely driven by the dominant predator types in our system—large predatory birds and invasive rats—as parents were more likely to leave nests with intrusion from these predator types.

Fine-scale plasticity in nest placement can compensate for poor quality junipers as nesting trees for gray vireos.

Understanding the interactions between behavior and habitat characteristics can have important implications for species of conservation concern. Gray vireos (Vireo vicinior) are one example of a species of conservation concern that is understudied in terms of nest survival probabilities and the habitat characteristics that influence them. Our objective was to determine if habitat features such as juniper density, juniper foliage density, or tree height influence nest survival probabilities, and if gray vireo nest placement can mitigate habitat risks. Based on previous work, we expected daily nest survival probabilities to be associated with nest height and surrounding vegetation. We monitored 89 nests in central New Mexico from 2016–2018 to estimate daily nest survival probabilities. We compared variation in nest placement, nest tree characteristics, and surrounding vegetation between failed and successful nests using logistic exposure models and Akaike Information Criteria. Daily and cumulative nest survival probability were 0.983 (95% CI [0.973–0.989]) and 0.575 (95% CI [0.444–0.702]), respectively. Top models predicting nest survival included a negative interaction between nest-tree foliage density and the distance of the nest from the edge of the nesting tree. This suggests that gray vireos can mitigate risks associated with low nest concealment by nesting closer to the interior of the nesting tree.

Predictors of Osprey Nest Success in a Highly Urbanized Environment

ABSTRACT Ospreys (Pandion haliaetus) are adaptable fish-eating raptors that readily nest on artificial structures in heavily human-dominated areas. Although the Osprey is a well-studied species, few researchers have investigated the factors that influence nest success and productivity in an urban environment. We monitored Osprey nests from 2013 to 2017 in highly urbanized Pinellas County, located on the west coast of central Florida, USA. We used logistic exposure models to assess the effects of timing of nesting, nest attributes (nest substrate, height), and landscape-level variables (inter-nest distance, distance to water, and surrounding habitat type) on daily survival rate (DSR) of Osprey nests. The number of active nests (i.e., nests with eggs) in the study area ranged from 53 in 2013 to 79 in 2016, with an overall total of 329 during the 5-yr study. Although most nests produced at least one young near fledging age, 131 of the nests failed. We attributed 45% of nest failures to storm events and 50% to unknown causes. The best logistic exposure model specification included only two variables: the discrete variable representing the date incubation started and the nominal variable indicating the year 2015. Osprey nests initiated earlier in the season were more likely to survive, and later nests (initiated after 22 April) averaged only one fledgling each. Osprey nests in 2015 had the highest DSR and relatively few failed due to storms. Our results supported previous research indicating that early nesters were more successful than late nesters. Our results also indicate that storms may play a role in nest success of Ospreys in Florida. Other variables, such as the amount of urbanized land surrounding Osprey nests did not appear to influence nest survival, indicating that Ospreys can be productive even in highly urban environments.

Nesting ecology and reproductive success of mixed-grass prairie songbirds

Vast areas of North American grasslands have been lost and degraded, resulting in unprecedented declines of biodiversity. For example, 82% of North American grassland songbird species are experiencing population declines. Basic natural history, life history, and demographic data from different regions and time periods are essential for modeling population dynamics and developing effective conservation strategies for grassland birds. We monitored 392 nests to provide information on nesting biology, quantify reproductive success, and gain insight into the extent to which predation and weather influence nest survival of 7 grassland songbird species in southwest Saskatchewan, during 2010 and 2011. Clutch sizes of all species were within the range reported previously and declined as the breeding season progressed, particularly for Chestnut-collared Longspur (Calcarius ornatus), Vesper (Pooecetes gramineus) and Baird's (Centronyx bairdii) sparrows, and Western Meadowlark (Sturnella neglecta). Overall, 32–69% of the nests we monitored were depredated, and predation accounted for 91% of all unsuccessful nesting attempts. Daily survival rates were lowest during the nestling stage for 5 species, and nest survival estimates ranged from 16% to 48%. Nest survival of 4 species was influenced by the temporal effects of age and date. Chestnut-collared Longspur and Western Meadowlark nest survival increased through early to mid-incubation and declined thereafter until ∼3 d prior to fledging before increasing again. Nest survival of these 2 species, along with Sprague's Pipit (Anthus spragueii) and Vesper Sparrow, were lowest in late June to early July. We found no support for a strong effect of precipitation on nest survival. However, nest survival rates declined with increasing ambient temperature for Chestnut-collared Longspur and Horned Lark (Eremophila alpestris), the 2 study species with the most exposed nests, and were highest for Western Meadowlark nests when ambient temperatures were between 15 and 24 °C.

Nesting ecology and reproductive success of mixed-grass prairie songbirds

Vast areas of North American grasslands have been lost and degraded, resulting in unprecedented declines of biodiversity. For example, 82% of North American grassland songbird species are experiencing population declines. Basic natural history, life history, and demographic data from different regions and time periods are essential for modeling population dynamics and developing effective conservation strategies for grassland birds. We monitored 392 nests to provide information on nesting biology, quantify reproductive success, and gain insight into the extent to which predation and weather influence nest survival of 7 grassland songbird species in southwest Saskatchewan, during 2010 and 2011. Clutch sizes of all species were within the range reported previously and declined as the breeding season progressed, particularly for Chestnut-collared Longspur (Calcarius ornatus), Vesper (Pooecetes gramineus) and Baird's (Centronyx bairdii) sparrows, and Western Meadowlark (Sturnella neglecta). Overall, 32–69% of the nests we monitored were depredated, and predation accounted for 91% of all unsuccessful nesting attempts. Daily survival rates were lowest during the nestling stage for 5 species, and nest survival estimates ranged from 16% to 48%. Nest survival of 4 species was influenced by the temporal effects of age and date. Chestnut-collared Longspur and Western Meadowlark nest survival increased through early to mid-incubation and declined thereafter until ∼3 d prior to fledging before increasing again. Nest survival of these 2 species, along with Sprague's Pipit (Anthus spragueii) and Vesper Sparrow, were lowest in late June to early July. We found no support for a strong effect of precipitation on nest survival. However, nest survival rates declined with increasing ambient temperature for Chestnut-collared Longspur and Horned Lark (Eremophila alpestris), the 2 study species with the most exposed nests, and were highest for Western Meadowlark nests when ambient temperatures were between 15 and 24 °C.

Does human scent bias the survival of bird nests?

Human‐scent contamination of bird nests and the human‐made trails leading to them is suspected to influence nest survival by attracting or deterring predatory mammals. This paper (1) reviews studies in which human‐scent contamination was suspected to have biased the survival of real and artificial nests by influencing the behaviour of predatory mammals, (2) summarizes the procedures used in attempts to mitigate human‐scent contamination in nest‐survival studies, and (3) describes procedures to enhance the design and interpretation of nest‐survival experiments. The behaviour of various non‐domesticated mammals is confirmed or suspected to be affected by human scent, so similar effects on nest predators are plausible. However, suggestions that human scent affects nest survival by influencing the behaviour of predatory mammals are poorly supported, due to a dearth of appropriately designed experiments. Some studies failed to include measures to reduce human‐scent contamination, and the effectiveness of scent‐mitigation methods used in other studies has seldom been verified. In addition, volatile compounds arising from soil and vegetation disturbed underfoot by field researchers may have confounded many nest‐survival studies. Investigators have routinely inferred human‐scent effects from post hoc predation patterns or have simply acknowledged possible human‐scent effects among other potential influences of nest fate. Studies are needed of the effects of human scent using uniform methods of scent application and verified methods of scent mitigation, where the fates of different types of nests are examined under a range of field conditions. More fundamentally, studies of naïve and experienced mammals are needed to assess their responses to human scent and clarify its salience in wildlife disturbance.

Low reproductive success of the endangered Iberá Seedeater in its only known breeding site, the Iberá Wetlands, Argentina

Abstract Subtropical grasslands are highly susceptible to habitat conversion and number among South America’s most threatened ecosystems. The grasslands of northeastern Argentina have been identified as a priority conservation area for threatened capuchino seedeaters because they constitute the main breeding area of these migratory birds. The Iberá Seedeater (Sporophila iberaensis) is a newly described species in the Iberá Wetlands in Argentina whose biology is still poorly understood. The endangered species inhabits grasslands but has only been reported to breed in the Iberá Wetlands ecoregion of northeastern Argentina. To explore the species’ association with grassland vegetation, we studied the breeding biology (clutch size, hatching success, and fledgling production) of the Iberá Seedeater and the main parameters that influence nest survival and nest-site selection. We conducted nest searches and banded adults and nestlings in Iberá National Park during the breeding seasons of 2016–2018. The breeding season of the Iberá Seedeater was highly synchronous and the cumulative probability of nest survival was 0.16. The daily nest survival rate decreased as the breeding season advanced, survival was lower for nests supported by Rhynchospora corymbosa than Paspalum durifolium, the two main nest substrates, and the main causes of nest failure were nest predation and strong winds. Additionally, the population exhibited male-biased site fidelity and a low female return rate. In contrast to other capuchinos, whose breeding biology is associated with upland grasslands, the Iberá Seedeater nested exclusively in flooded lowland grasslands on marsh plants. Thus, effective lowland grassland management is key to maintain the vegetation structure required for reproduction in the Iberá Seedeater.

Colony characteristics influence nest survival of Caribbean Roseate Terns

AbstractDetermining how site characteristics influence reproductive success can help guide conservation planning for declining wildlife populations. For colonially breeding seabirds, nest survival and predation risk can be influenced by both colony and nest site characteristics such as colony size, nest density, and nest location. We evaluated the reproductive success of a declining population of Roseate Terns (Sterna dougallii) in the United States and British Virgin Islands to identify primary causes of nest failure and investigate the influence of colony and nest site covariates on nest survival. In addition, we measured the influence of colony characteristics on chick provisioning to determine if resource competition in larger colonies affected foraging rates. Monitoring was conducted in 2017–2018 via motion-triggered cameras, which enable 24-hr monitoring with minimal nest disturbance. Nest survival was defined by both hatch success and early chick success, defined as a chick surviving from hatching through the fourth post-hatch day. We monitored 118 nests in 6 colonies over the 2 breeding seasons. We found that predation was the primary cause of nest failure. Both hatch and nest success increased with colony size, and neither nest survival nor predation probability was influenced by individual nest site characteristics. Provisioning rates were comparable among colony sites and did not vary with colony size. Our results suggest that directing management efforts toward enhancing colony size, rather than focusing on nest site characteristics, can be beneficial for tropical seabird conservation.

Drivers of nest survival in the Tawny-bellied Seedeater Sporophila hypoxantha (Aves: Thraupidae): time-specific factors are more related to success than ecological variables.

Tawny-bellied Seedeater (Sporophila hypoxantha) is an endangered (in Brazil) grassland dependent species, whose breeding success remains poorly known hampering conservation measures on its breeding grounds. Here we analyze the nest survival of the species in relation to temporal and environmental variables over three breeding seasons in hilly dry grasslands in southern Brazil. The apparent nest success was 40%, and MARK survival 20%. Predation was the main cause of failure, affecting 55% of the unsuccessful nests, followed by desertion, infestation by Philornis fly larvae, cattle trampling and burning. The productivity was 1.77 young per pair. Best models include time-specific factors (nest age and time of breeding season), reflected by a gradual reduction in nest survival over the nesting cycle, accompanied by an increase in temperature, subcutaneous larvae infestation, and predation. Nest site characteristics did not influence nest survival. Predation is more prevalent in the nestling rearing period than during incubation. This tendency may be caused by an increase in the activity in the nests, as is predicted by the Skutch hypothesis. The conclusion that time-specific factors influence nest survival more than ecological variables is important to plan on seasonally dependent conservation and management measures.