Urban-associated habitat alteration promotes brood parasitism of Acadian Flycatchers

ABSTRACT.   High rates of brood parasitism are generally associated with agricultural landscapes, but recent evidence suggests that urbanization may also increase the likelihood of brood parasitism. I evaluated the extent to which brood parasitism by Brown-headed Cowbirds ( Molothrus ater ) was explained by differences in (1) body size of adult hosts, presumably relating to the ability to defend nest from cowbirds, (2) nest placement in substrate and relative to habitat edges, (3) habitat structure surrounding nests, (4) host density, (5) cowbird abundance, both absolute and relative to host numbers, (6) landscape composition, and (7) Julian date. From 2001 to 2006, I monitored nest fate and measured vegetation characteristics surrounding nests of Acadian Flycatcher ( Empidonax virescens ) breeding in mature riparian forests in central Ohio, USA. The likelihood that a nest would be parasitized was best explained by the number of understory stems surrounding the nest and, to a lesser extent, by the amount of urbanization in the surrounding 1-km-radius landscape. Parasitized nests were surrounded by 1.6 times more stems and nearly twice the amount of urbanization than nonparasitized nests. Numbers of understory stems were positively associated with increasing urbanization, primarily due to invasion of urban forests by Amur honeysuckle ( Lonicera maackii ). Thus, urban-associated changes in habitat characteristics around nests may be important contributors to the greater vulnerability of urban nests to brood parasitism than nests in more rural landscapes. This pattern suggests that ecological restoration, such as removing exotic shrubs, may be an effective strategy to ameliorate certain negative consequences of urbanization near wooded reserves.     

Exotic shrubs as ephemeral ecological traps for nesting birds

Certain exotic plants may increase risk of nest predation, and, in this way, may act as ecological traps. We hypothesized that the greater vulnerability to predation was a consequence of either (1) reduced nest height due to architectural differences among plant species or (2) seasonal changes in the distribution of nests among forest strata. To test this, we examined temporal variation in nest survival of 888 nests of Northern Cardinal (Cardinalis cardinalis) in native substrates and two exotic shrubs (Lonicera maackii and Rosa multiflora) in Ohio, USA, 2001–2006. We evaluated evidence for an ecological trap by monitoring the annual reproductive productivity of 245 breeding pairs of cardinals. Only nests in Rosa experienced relatively constant survival rates across the season, whereas probability of survival increased over the season for nests in other substrates. Interestingly, the relative vulnerability of nests in different substrates varied across the season. Most strikingly, nests in Lonicera in early spring showed the lowest survival rates but exceeded survival rates of nests in native substrates late in the season. Nest height failed to explain seasonal changes in nest survival, as only nests in native plants significantly increased in height as the season progressed. Rather, predation risk seemed to be a function of the proportion of nests within each substrate, as illustrated by the decreased predation in Lonicera as the relative proportion of nests in native substrates increased. The patterns of temporal variation in predation risk that we detected show that impacts of Lonicera are not a function of plant architecture alone and may be related to leaf phenology, changes in nest density, nest site location, and/or nest synchrony. Examination of the reproductive productivity of cardinals showed that pairs that made their first nest attempt in Lonicera fledged 20% fewer cardinal young than birds that began the season using other substrates. Thus, we suggest that exotic plants may represent an ephemeral ecological trap for certain nesting birds, where negative effects persist only during certain periods.     

Urban living influences the nesting success of Darwin’s finches in the Galápagos Islands

Urbanization is expanding worldwide with major consequences for organisms. Anthropogenic factors can reduce the fitness of animals but may have benefits, such as consistent human food availability. Understanding anthropogenic trade‐offs is critical in environments with variable levels of natural food availability, such as the Galápagos Islands, an area of rapid urbanization. For example, during dry years, the reproductive success of bird species, such as Darwin''s finches, is low because reduced precipitation impacts food availability. Urban areas provide supplemental human food to finches, which could improve their reproductive success during years with low natural food availability. However, urban finches might face trade‐offs, such as the incorporation of anthropogenic debris (e.g., string, plastic) into their nests, which may increase mortality. In our study, we determined the effect of urbanization on the nesting success of small ground finches (Geospiza fuliginosa; a species of Darwin''s finch) during a dry year on San Cristóbal Island. We quantified nest building, egg laying and hatching, and fledging in an urban and nonurban area and characterized the anthropogenic debris in nests. We also documented mortalities including nest trash‐related deaths and whether anthropogenic materials directly led to entanglement‐ or ingestion‐related nest mortalities. Overall, urban finches built more nests, laid more eggs, and produced more fledglings than nonurban finches. However, every nest in the urban area contained anthropogenic material, which resulted in 18% nestling mortality while nonurban nests had no anthropogenic debris. Our study showed that urban living has trade‐offs: urban birds have overall higher nesting success during a dry year than nonurban birds, but urban birds can suffer mortality from anthropogenic‐related nest‐materials. These results suggest that despite potential costs, finches benefit overall from urban living and urbanization may buffer the effects of limited resource availability in the Galápagos Islands.     

Behavioral responses of nesting birds to human disturbance along recreational trails

ABSTRACT The presence of recreational trails can impact breeding birds either indirectly by altering habitat or the movement patterns of predators or directly if the presence of humans disturbs birds. We examined the behavioral responses of nesting female Northern Cardinals (Cardinalis cardinalis) to human disturbance using both experimental and observational approaches. From April to August 2006 and 2007, we monitored Northern Cardinal nests in 18 riparian forests in Ohio, USA. Two experimental trials were conducted at each nest (N= 63), with Flight Initiation Distance (FID, the distance at which a bird flushed from the nest) recorded as we approached nests by walking directly toward them and by walking along trails located variable distances from nests. We also measured flight initiation distance (FID) when nests were approached during routine nest checks (N= 160). Cardinals were six times more likely to flush when nests were approached directly, and females on higher nests were less likely to flush regardless of distance to trail. FID was not significantly influenced by the distance of nests from trails. We found no association between nest survival and the tendency of birds to flush. Rather, nest survival was best explained by nest height. Thus, our findings suggest that the responses of birds to human use of recreational trails have only short‐term effects, with no apparent effects of on nest survival. Because the reaction of birds to humans in our study depended on how nests were approached, studies where FID is used as an indicator of sensitivity to human disturbance and is determined by direct approaches may overestimate the potential impact of trails on nesting birds.     

Waterfowl Nesting in Fall-Seeded and Spring-Seeded Cropland in Saskatchewan

Abstract: Waterfowl nesting in annual croplands has remained a little-known aspect of waterfowl nesting ecology because of the inability of many studies to systematically search this habitat through the nesting season. Where searches have been conducted, they are generally restricted to the period prior to seeding, and many nests found are destroyed by the seeding operation. Consequently, fall-seeded crops have been promoted as an alternative cropping practice that could increase nest survival of waterfowl nesting in croplands. During 1996–1999, we conducted 3–4 complete nest searches on 4,274 ha of cropland, including spring-seeded wheat and barley, winter wheat, and fall rye in southern Saskatchewan, Canada. Using suites of predictive models, we tested hypotheses regarding relative nest abundance and nest survival among crop types and tested the influence of several landscape-scale covariates on these metrics. Apparent nest densities were higher in fall-seeded crops (winter wheat: 0.39 nests/ha, fall rye: 0.25 nests/ha) than in spring-seeded crops (0.03 nests/ha), and nest density in spring-seeded croplands increased with percent cropland and percent wetland habitat in the surrounding landscape. Nest survival was higher in winter wheat (38%) than in either fall rye (18%) or spring-seeded crops (12%), and nest survival in spring-seeded crops increased with relative nest initiation date. Nest survival was unaffected by surrounding landscape characteristics but tended to be higher in years of average wetness. Based on our findings, winter wheat and fall rye have the potential to provide productive nesting habitat for ≥7 species of upland nesting ducks and fall-seeded crops are a conservation tool well suited to highly cropped landscapes.     

The effectiveness of volunteer nest protection on the nest success of Northern Lapwings Vanellus vanellus on Dutch arable farms

Clutches of ground‐nesting farmland birds are often destroyed by farming operations, resulting in insufficient reproductive success and subsequently declining populations. The aim of this study was to investigate whether volunteer nest protection can enhance nest success of ground‐nesting birds. The study compared nest success of protected and unprotected Northern Lapwing Vanellus vanellus nests over 2 years on arable farms in the Netherlands. Because of different crop management, nest success of ground‐breeding birds might differ between organic and conventional arable farms. The effectiveness of volunteer nest protection was therefore investigated on both farm types. Although nest protection significantly reduced nest loss due to farming operations, there were no significant differences in total clutch survival of protected and unprotected nests. However, sample sizes of unprotected nests, and protected nests on organic farms, were relatively small, which may have reduced statistical power. There were indications that protected nests were predated or deserted more often. We recommend exploring different ways to improve the effectiveness of volunteer nest protection through a further reduction of nest loss due to farming operations and predation.     

Use of mistletoes by the Grey Go‐away‐bird (Corythaixoides concolor,Musophagidae) in a semi‐arid savannah,south‐west Zimbabwe

Mistletoes are preferred nesting sites for many bird species in a range of habitats. However, no studies have examined the use of mistletoes by nesting birds in the semi‐arid savannah. We studied nesting in mistletoe and its role in determining nesting success in the Grey Go‐away‐bird in south‐west Zimbabwe. We modelled the effects of mistletoe, mistletoe abundance, nest microclimate, concealment and nest height on daily survival rates (DSR) using program MARK. A constant survival model was best fitted for the Grey Go‐away‐bird suggesting a constant nest survival rate across the nesting period. Mistletoe nests had lower DSR than nests placed elsewhere in the canopy. Mistletoe abundance and nest height had a positive association with DSR whereas visibility distance, microclimate and concealment were negatively associated with DSR. Overall, survival for nests in mistletoe was 22.1% compared with 90.5% for nests in other substrates over the 50‐day nesting period. In conclusion, the low nest survival in mistletoe suggests either that the factors used to select mistletoe as nest sites by these birds are poor predictors of nest success or that nesting in mistletoe may be maladaptive.     

Factors Affecting Daily Nest Survival of Burrowing Owls Within Black-Tailed Prairie Dog Colonies

ABSTRACT Identifying environmental parameters that influence probability of nest predation is important for developing and implementing effective management strategies for species of conservation concern. We estimated daily nest survival for a migratory population of burrowing owls (Athene cunicularia) breeding in black-tailed prairie dog (Cynomys ludovicianus) colonies in Wyoming, USA. We compared estimates based on 3 common approaches: apparent nesting success, Mayfield estimates, and a model-based logistic-exposure approach. We also examined whether 8 intrinsic and extrinsic factors affected daily nest survival in burrowing owls. Positive biases in apparent nest survival were low (3–6%), probably because prior knowledge of nest locations and colonial behavior among nesting pairs facilitated discovery of most nests early in the nesting cycle. Daily nest survival increased as the breeding season progressed, was negatively correlated with ambient temperature, was positively correlated with nest-burrow tunnel length, and decreased as the nesting cycle progressed. Environmental features were similar between failed and successful nests based on 95% confidence intervals, but the seasonal midpoint was earlier for failed nests (31 May) compared to successful nests (15 Jun). The large annual variation in nest survival (a 15.3% increase between 2003 and 2004) accentuates the importance of multiyear studies when estimating reproductive parameters and when examining the factors that affect those parameters. Failure to locate and monitor nests throughout the breeding season may yield biased estimates of nesting success in burrowing owls (and possibly other species), and some of the variation in nesting success among years and across study sites may be explained by annual and spatial variation in ambient temperature. Any management actions that result in fewer prairie dogs, shorter burrow lengths, or earlier nesting may adversely affect reproductive success of burrowing owls.     

Effect of floating nest platforms on the breeding performance of Black Terns

ABSTRACT.   In 2003 and 2004, we placed 41 floating nest platforms on Grassy Lake in southeastern Wisconsin (USA) to test the hypothesis that reproductive success of Black Terns ( Chlidonias niger ) is limited by the quality of suitable nesting habitat. Extreme differences in water levels between these 2 yr provided a natural experiment to evaluate the effectiveness of the nest platforms during a drought year (2003) when natural nesting substrate was abundant, and a flood year (2004) when natural substrate was limited during the peak nesting period. Terns nested on 27 of 41 (66%) of the platforms in 2003 and 26 of 41 (63%) in 2004. No difference in the occupancy rate of platforms and natural nests was evident in 2003, but the pattern of clutch initiations early in the season in 2004 indicated that platforms were preferred over natural substrates. In 2003, nest survival rates did not differ between nests placed on platforms and those placed on natural substrates, but platform nests had significantly higher hatching success and nest survival rates in 2004. Both the Kaplan-Meier and Apparent Nest Success methods of calculating nest survival provided similar estimates. In both years, eggs laid on platforms were significantly larger than those laid on natural substrates, suggesting that platforms were occupied by high-quality birds. Our study indicates that floating nest platforms can be an effective management tool to enhance nesting habitat for Black Terns and other aquatic birds that construct floating nests, primarily because platforms provide nest sites when natural sites are not available due to flooding. Nest platforms also may be useful for addressing questions concerning habitat selection and parental quality.     

Nest‐site selection and productivity of Vesper Sparrows breeding in grazed habitats

ABSTRACT Livestock grazing in the shortgrass steppe of the Intermountain region of British Columbia may have a negative impact on ground‐nesting birds, but evidence of such an impact is lacking. We examined nest‐site selection and productivity of ground‐nesting Vesper Sparrows (Pooecetes gramineus) across sites with different grazing histories. From 2006 to 2008, we monitored Vesper Sparrow nests and measured vegetation characteristics known to be affected by grazing within nest patches. We used an information‐theoretic approach to test the relative importance of grazing‐affected vegetation variables as predictors of nest‐site selection, nest survival, and nestling condition. Vesper Sparrows selected nest sites with greater cover of late‐seral grass species that decrease in occurrence in response to grazing (i.e., “decreasers”) than was available in random patches in the same territories. Daily nest survival was also lower for nests surrounded by shorter vegetation (odds ratio = 1.12). However, “decreaser” cover was not associated with either of the two indices of productivity measured (daily nest survival probability and nestling condition). In addition, vegetation height, although an important driver of success, was not linked with nest‐site selection, and no vegetation‐cover variable was positively associated with productivity, despite nest concealment being central to our predictions. This suggests that predation risk for nests in areas with shorter vegetation was being elevated through some factor unrelated to concealment. Our results show that grazing reduced both the availability of suitable habitat for and nesting success of Vesper Sparrows, indicating that grazing could pose a threat to population persistence at a broader scale and could potentially contribute to observed declines. Additional research is needed to determine if grazing guidelines in the Intermountain region of British Columbia should be amended, better enforced, or both to prevent regional declines in populations of ground‐nesting grassland birds.     

Nest positioning by male Daito White‐eyes Zosterops japonicus daitoensis improves with age to reduce nest predation risk

Age‐related improvement in reproductive success is widely observed in birds, and the mechanisms by which productivity is enhanced have received considerable attention. However, little is known about how parental age affects the loss of eggs or nestlings despite the fact that age effects on nesting success are often reported. We examined parental age effects on reproductive success in relation to the avoidance of nest predation in an island subspecies of the Japanese White‐eye, the Daito White‐eye Zosterops japonicus daitoensis. Clutch size and annual number of breeding attempts did not differ between parental age classes. Reproductive success was affected only by male age through an increase in nesting success. Nest failure was attributed only to predation in this species and nest concealment and nest height were important nest characteristics promoting successful fledging. Older males built their nests in more concealed and higher positions than first‐year birds, regardless of vegetation status around the nest. Analysis of individual birds suggested that by shifting the nest to a safer position, male White‐eyes achieved higher nesting success than in the previous year. Of three hypotheses of age‐related improvement in reproductive success considered, our data favoured the hypothesis that as individuals grow older, their breeding competence improves.     

Avian productivity in urban landscapes: a review and meta-analysis

There is an urgent need to thoroughly review and comprehend the effects of urbanization on wildlife in order to understand both the ecological implications of increasing urbanization and how to mitigate its threat to biodiversity globally. We examined patterns in comparative productivity of urban and non-urban passerine birds, using published estimates from paired comparisons, and by reviewing and developing explanations in terms of resources, competitors, predators and other specifically urban environmental factors. The most consistent patterns were for earlier lay dates, lower clutch size, lower nestling weight and lower productivity per nesting attempt in urban landscapes; these were supported by a formal meta-analysis. Nest failure rates did not show consistent patterns across the species considered. We suggest that food availability is a key driver of differences in passerine demography between landscapes. In urban habitats, human-provided food may improve adult condition over winter, leading to earlier lay dates and, in some species, to higher survival and higher breeding densities, but paucity of natural food may lead to lower productivity per nesting attempt. We demonstrate that additional comparative research is needed on a wider range of species, on the effects of natural and human-provided food availability, and on the differences in survival and dispersal between urban and non-urban populations. Importantly, better-targeted research and monitoring is needed in areas that are at greatest threat from urbanization, especially in the developing world.     

Nest sites as limiting resources for cavity‐nesting birds in mature forest ecosystems: a review of the evidence

ABSTRACT Assumptions that populations of cavity‐nesting birds are limited by access to nest sites have largely been based on anecdotal reports or correlative data. Nest‐box‐addition experiments or tree‐cavity‐blocking experiments are potentially rigorous ways to investigate how densities of breeding birds are affected by access to nest cavities. Experimental evidence indicates that natural tree holes are limited in human‐altered landscapes, but the possibility that cavity nests are limited in old growth (unmanaged) forests is less clear. I reviewed 31 nest‐cavity‐removal or addition experiments conducted with 20 species of cavity‐nesting birds in mature forests. Of these 31 experiments conducted with a variety of different species of birds, only 19% reported statistically significant changes in breeding densities. However, none of these studies included data about the reproductive history of individuals colonizing the boxes (i.e., whether birds using the boxes would have otherwise been floaters or that birds excluded from blocked cavities on the plots did not simply move elsewhere), so they provided no strong evidence that the number of breeding pairs was limited by availability of nest sites at the population scale. Although some studies indicate that nest sites are limited at local (plot) scales in old growth forests, there is still little empirical evidence for nest‐site limitation at the population‐ and landscape‐level in mature, unmanaged forests. I review the challenges in designing and interpreting box‐addition experiments and highlight the main gaps in knowledge that should be targeted in the future.     

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.     

城市化对鸟类筑巢的影响研究综述

繁殖期筑巢是鸟类生活史的重要阶段, 是鸟类繁殖成功的关键保障。全球范围的城市化加速推进, 使城市中筑巢繁殖的鸟类面临挑战的同时又为其提供了特殊机遇。本文通过搜索现有文献, 利用Biblioshiny程序提取并整合关键词, 得到城市鸟类生态研究的热点领域, 分析了城市气候、食物资源、巢址资源、捕食压力、污染和人为干扰对鸟类筑巢的影响, 并对今后城市化对鸟类筑巢影响研究中亟需解决的问题进行了展望。城市化对鸟类筑巢期、巢址选择及巢材选择产生显著影响, 与栖息在村镇生境的鸟类相比, 在城市中繁殖的鸟类在筑巢时间、空间和巢材使用上出现变化。在城市中筑巢的鸟类到底是通过调整行为策略作出积极适应, 还是被动接受城市环境中的诸多负面干扰, 需要针对研究对象和特定的城市栖息生境进行及时评估, 而非泛泛之谈。要在研究结论基础上, 深入思考并提出城市化建设过程中有利于鸟类种群和群落保护的具体措施, 高效发挥公民科学作用以解决城市中的鸟类保护实践问题。     

Use of Restored Riparian Habitat by the Endangered Least Bell's Vireo (Vireo bellii pusillus)

A primary objective of riparian restoration in California is the creation of habitat for endangered species. Four restoration sites in San Diego County were monitored between 1989 and 1993 and evaluated for their suitability as nesting habitat for Vireo bellii pusillus (Least Bell's Vireo), a state and federally endangered obligate riparian breeder. Vegetation structure at each site was quantified annually and compared to a model of canopy architecture derived from Least Bell's Vireo territories in natural habitat. Vireo use of restored habitat was documented through systematic surveys and nest monitoring. By 1993, only one site in its entirety met the habitat suitability criteria of the model, but portions of each site during all years did so. Differences between sites in the time required to develop suitable habitat—well-developed layered vegetation from the ground to under 8m in height)—were attributable largely to variation in annual rainfall. Vireos visited restoration sites to forage as early as the first growing season, but they did not establish territories or nest there until at least part of the site supported suitable habitat as determined from the model. Placement of territories and nests coincided with patches of dense vegetation characteristic of natural nesting areas. Occupation of restored sites was accelerated by the presence of adjacent mature riparian habitat, which afforded birds nest sites and/or foraging habitat lacking in the planted vegetation. Vireos nesting in restored habitat achieved success comparable to that of vireos nesting in surrounding natural habitat, and there was no evidence that productivity was reduced in created areas. These findings indicate that creating nesting habitat for this target species is feasible and suggest that the critical components of vireo nesting habitat have been captured in both the design and quantitative assessment of restoration sites.     

Nest survival rates of Red‐crested Cardinals increase with nest age in south‐temperate forests of Argentina

ABSTRACT The main cause of nest mortality for most bird species is predation and nest survival rates often vary in relation to time‐specific variables. Few investigators have examined time‐specific patterns of nest survival in Neotropical birds, and most such studies have focused on tropical and subtropical species. To better understand age‐related patterns of nest survival, we studied nest survival of Red‐crested Cardinals (Paroaria coronata, Thraupidae) in a south‐temperate forest in Argentina. We modeled daily nest survival rates (DSR) using program MARK. We examined the relationship between nest age and nest survival rate, controlling for the effects of physical characteristics of nest sites and progression of the breeding season. We monitored 367 nests for a total of 4018 exposure days. We found that DSR increased with nest age and was higher in small isolated patches than in large continuous patches of forests. The increase of DSR with nest age could be a consequence of more vulnerable nests being predated early in the nesting cycle or a result of parents defending nests more vigorously as nestlings age because of their increasing reproductive value. Open areas of grassland that surrounded the small isolated patches of forests in our study may have been a barrier to predator movements, possibly explaining the lower predation rates. Nest survival rates in our study were lower than those reported for tropical or Nearctic temperate birds, but similar to those reported in other studies of Neotropical temperate birds. Reasons for the low nest survival rates of Neotropical temperate birds remain unclear, and additional studies of predator communities are needed to help elucidate this topic.     

A description of nesting behaviors,including factors impacting nest site selection,in black‐and‐white ruffed lemurs (Varecia variegata)

Nest site selection is at once fundamental to reproduction and a poorly understood component of many organisms’ reproductive investment. This study investigates the nesting behaviors of black‐and‐white ruffed lemurs, Varecia variegata, a litter‐bearing primate from the southeastern rainforests of Madagascar. Using a combination of behavioral, geospatial, and demographic data, I test the hypotheses that environmental and social cues influence nest site selection and that these decisions ultimately impact maternal reproductive success. Gestating females built multiple large nests throughout their territories. Of these, females used only a fraction of the originally constructed nests, as well as several parking locations as infants aged. Nest construction was best predicted by environmental cues, including the size of the nesting tree and density of feeding trees within a 75 m radius of the nest, whereas nest use depended largely on the size and average distance to feeding trees within that same area. Microhabitat characteristics were unrelated to whether females built or used nests. Although unrelated to nest site selection, social cues, specifically the average distance to conspecifics’ nest and park sites, were related to maternal reproductive success; mothers whose litters were parked in closer proximity to others’ nests experienced higher infant survival than those whose nests were more isolated. This is likely because nesting proximity facilitated communal crèche use by neighboring females. Together, these results suggest a complex pattern of nesting behaviors that involves females strategically building nests in areas with high potential resource abundance, using nests in areas according to their realized productivity, and communally rearing infants within a network of nests distributed throughout the larger communal territory.     

The reproductive success of sandhill cranes in midwestern landscapes

A number of wildlife species have recovered from the brink of extinction to flourish and, in some cases, even become a commonly recognized urban species (e.g., Canada goose [Branta canadensis]). Broadly extirpated from much of their historical range in North America, the sandhill crane (Antigone canadensis) demonstrated this potential for population recovery. The trajectory of the eastern population of greater sandhill cranes is remarkable—perhaps as many as 90,000 cranes now occur throughout the same Great Lakes states that reported only dozens of birds less than a century ago. However, understanding future population growth of the species remains uncertain because breeding birds are increasingly exposed to the pressures of urban sprawl and a changing agricultural landscape. From 2009 to 2014 we investigated the survival of sandhill crane nests and young up to 11 weeks of age (the point at which they are capable of flight) in the core of the eastern population's range in central Wisconsin and at its peripheral extent in a rapidly developing urban region of northeastern Illinois, USA. We located crane nests via systematic surveys on foot and from helicopters, we then radio-tagged the young and monitored them until they died or were capable to sustained flight. Overall, young were more likely to hatch from nests in Illinois (60%) than in central Wisconsin (46%), regardless of differences in land cover surrounding the nest site. In contrast, the survivorship of young was positively correlated with urban land cover in both regions but higher in central Wisconsin (54%) than in northeast Illinois (27%). Overall, the probability of producing young was greater in landscapes with more urban development, regardless of region. We suggest that differences in predator composition, predator behavior, and crane density between rural and urban areas is the primary reason for the difference in crane productivity. Higher recruitment of sandhill cranes using urban landscapes may allow cranes to echo the population trajectory of urban Canada geese. We anticipate that sandhill cranes will continue to use urban landscapes, and likely expand their geographic range as breeding pairs benefit from the increased survivorship of young in those landscapes. © The Wildlife Society, 2019     

Edge effects reduce the nesting success of Acadian Flycatchers in a moderately fragmented forest

ABSTRACT.   Forest fragmentation can create negative edge effects that reduce the reproductive success of birds nesting near the forest/nonforest interface, and threaten bird populations deeper in remnant forest habitats. Negative edge effects may be more pronounced in landscapes that are moderately fragmented, particularly where agriculture is the primary land-use fragmenting forests. Information about the extent and strength of edge effects at a site can help guide conservation actions, and determine their effectiveness. We examined edge effects for birds breeding in a nearly contiguous forest fragmented by relatively narrow agricultural corridors in Illinois (USA). We measured rates of nest predation and brood parasitism for Acadian Flycatchers ( Empidonax virescens ) over a continuum of distances from the edge of an agricultural inholding. Nest predation and brood parasitism were highest near the edge and decreased with increasing distance from the edge. Given the cumulative effects of nest predation and brood parasitism on reproductive success, we determined that forest within 600 m of the inholding was sink habitat. We found, however, that deeper forest interior areas currently serve as source habitat, and that conversion of the entire 205 ha agricultural corridor to forest would add 1350 ha of source habitat for Acadian Flycatchers. Such results provide support for a local conservation strategy of forest consolidation and establish baseline measures necessary to determine the relative effectiveness of any subsequent reforestation efforts.