Dolichonyx Research Articles

David F. DeSante’s Birds of Cabo San Lucas, Fall 1968: A Historic Account

In preparation for his doctoral studies at Stanford University, the late David F. DeSante spent the fall of 1968 studying migratory landbirds at Cabo San Lucas. Although his hopes to capture numerous vagrant warblers were not met, he amassed an impressive list of distributional records for the Baja California Peninsula at a time when few ornithologists were working there. Among these were peninsular firsts for the Ring-necked Duck (Aythya collaris), Broad-billed Hummingbird (Cynanthus latirostris), Broad-winged Hawk (Buteo platypterus), Bobolink (Dolichonyx oryzivorus), and Painted Bunting (Passerina ciris). Another six species, and one subspecies, were found for the first time in Baja California Sur. Venturing away from the immediate confines of Cabo San Lucas, DeSante established the first peninsular record of the Gray-headed Junco (Junco hyemalis caniceps) and first state records for another five species and one subspecies. Although many of these records have been reported previously, the junior authors believe it is appropriate to synthesize them more completely with current context, in Dave’s honor.

Trending against the grain: Bird population responses to expanding energy portfolios in the US Northern Great Plains.

Future global energy demand may be met through increased extraction of fossil fuels and production of renewable energy such as biofuels. Renewable energy from biofuels is often proposed as an environmentally friendly alternative to fossil fuels; however, impacts of renewable energy sources on wildlife populations have rarely been evaluated in working landscapes. We used North American Breeding Bird Survey data (1998 to 2021) to assess whether the joint effects of oil and gas and biofuel crop production explained grassland bird population declines. We modeled location-specific effects of land use on grassland bird habitat use for four grassland bird species (bobolink [Dolichonyx oryzivorus], grasshopper sparrow [Ammodramus savannarum], Savannah sparrow [Passerculus sandwichensis], and western meadowlark [Sturnella neglecta]) in North Dakota, a state experiencing rapid growth in both energy sectors. Our analysis showed that grassland birds responded more negatively to biofuel feedstocks (i.e., corn and soybeans) on the landscape compared with oil and gas development. Furthermore, we found that the effect of feedstocks was not generalizable to other forms of agricultural land use. When combined, these land use changes resulted in distributional shifts of grassland birds, with use by birds being lower in regions dominated by biofuel production, which appears partially responsible for observed abundance trends at the state level. Our results indicate that expansion of oil and gas development has negatively affected habitat use by some grassland birds, but this impact was more localized when compared to biofuel crops. Conservation practitioners may need to adapt their conservation strategies to account for widespread and rapid land use change driven by United States energy policies.

Management of U.S. Agricultural Lands Differentially Affects Avian Habitat Connectivity

Despite frequently being implicated in species declines, agricultural lands may nonetheless play an important role in connecting wildlife populations by serving as movement corridors or stopover sites between areas of high-quality habitat. For many North American bird species, agricultural intensification over the past half century has substantially impacted populations, yet recent studies have noted the potential for supporting avian biodiversity on agricultural lands through the promotion of functional connectivity. To support avian conservation efforts on agricultural lands across the United States, we used publicly available data from eBird to quantify and map the effects of agriculture on habitat suitability (using random forest models) and functional connectivity (via circuit theory) for three focal species that have experienced agriculture-linked declines or range contractions in recent decades: Greater Sage-grouse (Centrocercus urophasianus), American Black Duck (Anas rubripes), and Bobolink (Dolichonyx oryzivorus). Our analysis drew on novel, remotely sensed estimates of agricultural management intensity to quantify the effects of management practices on avian habitat and movement, revealing complex, species-specific relationships between agriculture and habitat value for the three focal species. Rangelands and croplands exhibited relatively high connectivity values for Greater Sage-grouse and Bobolink, respectively, mirroring these species’ strong habitat preferences for open sagebrush and cultivated grasslands. By contrast, American Black Duck migratory connectivity was low on all agricultural cover types. Mapping our model results across each species’ geographic range in the U.S. revealed key areas for agricultural management action to preserve high-quality habitat and connectivity, and we link these spatial recommendations to government incentive programs that can be used to increase wildlife-friendly management on U.S. agricultural lands.

Impact of grazing and conservation opportunities for nesting grassland birds in a community pasture

Multiple bird species-at-risk nest on the ground in hayfields and pastures, making nests susceptible to inadvertent destruction from agricultural activity (e.g., trampling by livestock). To better understand the impact of Domestic Cattle (Bos taurus) grazing, we assessed the distribution and breeding status of nesting grassland birds in 2019 and 2020 at the Grey Dufferin Community Pasture, a ~234 ha pasture in southern Ontario, Canada. We estimated there were 86 male Bobolink (Dolichonyx oryzivorus) in the community pasture in 2019 and 100 in 2020 before grazing began; observed abundance decreased by 73% in fields after grazing in 2020. Eastern Meadowlark (Sturnella magna) maintained territories after grazing and fledged young in 67% (n = 21) of territories. Savannah Sparrow (Passerculus sandwichensis) was common across the community pasture before and after grazing occurred. We detected evidence of nesting more frequently in Bobolink and Savannah Sparrow territories in ungrazed than in grazed fields. Our results support previous research indicating nesting Bobolink often disperse from moderately to heavily grazed fields, whereas Eastern Meadowlark and Savannah Sparrow largely remain and renest. Despite the inadvertent negative impacts of cattle stepping or laying on nests and consuming vegetative cover, the community pasture provides areas for successful nesting, with Eastern Meadowlark faring better than Bobolink. Flexibility in the timing and duration of grazing in rotational grazing systems may enable strategic management in target fields (e.g., maintaining enough vegetation for nesting Bobolink). Information about the distribution and abundance of birds can be used to target particular fields for conservation.

Breeding origins of a uniquely regular migrant songbird in the Galápagos Islands.

Little is known about the causes and consequences of alternative pathways flown by long-distance migratory birds. Bobolinks (Dolichonyx oryzivorus) breed in grasslands across northern North America and migrate from their breeding grounds toward the eastern Atlantic Coast and then proceed through the Caribbean to South America. However, a small but regular number of Bobolinks have been recorded on the Galapagos Islands. We collected genetic samples from nine Galapagos Bobolinks and performed double-digest restriction site-associated sequencing. We compared them with samples from seven locations across their breeding distribution to determine their population of origin. Galapagos Bobolinks shared the genetic structure of a cluster in the eastern portion of the breeding range that includes New Brunswick and Ontario, Canada, and Vermont, United States. Genetic assignment tests largely corroborated this finding, although slightly different results were obtained for the two methods. All individuals were assigned to the Ontario breeding population using AssignPop, while Rubias assigned six of the migrants to Ontario and three to a Midwest breeding population. Low average relatedness among Galapagos individuals indicates that they are not more related to one another than to individuals within a breeding population and are therefore likely not from a single, small isolated population. Our results do not support the probability hypothesis-that Galapagos Bobolinks originated from the region that includes the greatest proportion of their breeding range (Great Plains)-or the vagrant hypothesis-that migrants are displaced onto Galapagos due to weather events. Instead, our findings support the proximity hypothesis, where migrants originate from the geographically closest-breeding populations.

Variation in body size and plumage does not explain apparent survival for a long-distance migratory songbird, the Bobolink (Dolichonyx oryzivorus)

El tordo charlatán (Dolichonyx oryzivorus) es un ave canora de pastizal migratoria de larga distancia cuya población global está en declive a largo plazo, principalmente debido a la pérdida de hábitat y a la intensificación de las prácticas agrícolas. Para entender mejor los factores que afectan su ciclo anual, utilizamos una población con edad conocida de tordos charlatanes machos (n = 121) que se reproducían en pastizales agrícolas de Vermont y exploramos cómo la variación en su plumaje (la extensión del amarillo de su capucha) y la morfología corporal (masa corporal y longitud del ala) explicaban la variación en la sobrevivencia aparente. La masa corporal del tordo charlatán y la longitud del ala variaron entre los años 2–5. El tamaño de la capucha del tordo charlatán no tuvo variaciones con la edad. Sin embargo, ninguno de los 3 caracteres morfológicos explicaba la variación de sobrevivencia aparente. Nuestros resultados resaltan los desafíos asociados a entender la variación en la calidad de los individuos relativa a la edad, particularmente con respecto a factores que afectan procesos demográficos de especies en declive. Palabras clave: ala, Icteridae, masa, morfología, plumaje, Programa MARK, Vermont.

Microsatellite markers yield new insight into extra-pair paternity in Bobolinks (Dolichonyx oryzivorus)

Since the mid-1980s, our understanding of avian reproductive strategies has shifted as new molecular technologies have revealed how common promiscuity is in many monogamous avian species. However, the prevalence and importance of extra-pair paternity in polygynous species is less well studied. We used microsatellite loci from related icterid species to identify the extra-pair paternity rate in a polygynous population of Bobolinks (Dolichonyx oryzivorus) that bred in the Champlain Valley of Vermont from 2002 to 2018. We assigned paternity for 120 nestlings and found that 42% of nestlings were sired by extra-pair males. These results highlight the importance of extra-pair paternity in the reproductive behavior of Bobolinks that breed in agricultural habitats.

Hay Nutritional Quality and Grassland Bird Nesting: Impact of Delaying First Hay Cut on Dairy and Beef Production in Ontario

Perennial forage production exists in Ontario to support the livestock industry, but also provides nesting habitat for grassland birds such as the threatened Bobolink (Dolichonyx oryzivorus) and Eastern Meadowlark (Sturnella magna). Delaying hay harvest until July 15 or later allows most nestling birds to leave the nest, but the nutritional value of hay decreases substantially. This project estimated the nutritional and economic impact of delaying the first hay cut until after July 15 on beef and dairy production in Ontario, Canada. Forage crops were sampled across Ontario, analysis of nutritional value performed, and effects on production and economics modelled. 634 samples were collected over 13 weeks at 16 sites from May 21 to August 14 during 2014 and 2015. As expected, nutritional quality declined over the season. Crude protein decreased by 5.2%, total digestible nutrients by 7.7%, neutral detergent fibre digestibility (NDFd48) by 20.1%, while lignin increased by 3.5%, neutral detergent fibre by 13.1%, and acid detergent fibre by 9.9%. Estimated yearly milk production decreased 10.9 kg or C$7.87/dairy cow for each day of delay in harvest (2017 values). Estimated growth of backgrounding beef steers decreased 1.56 kg or C$5.49/head for each day of delay in harvest. This translated into lost revenue per acre for backgrounding steers of C$31 per acre and C$45 per acre for over wintering beef cows for a delay from mid-June to mid-July. Some agri-environmental incentives in Canada, US and Europe offset the reduced revenue due to lower quality forages. This analysis informs farmers about the cost of practices to benefit grassland birds and provides empirical data on how to structure stewardship incentives for these practices.

Age-specific effects on reproductive performance of grassland songbirds nesting in agricultural habitats

Clutch size and number of young fledged has been shown to increase with female age until approximately mid-life, when reproductive performance declines. We used a long-term dataset (2002–019) to investigate age-specific effects on reproductive parameters of known-age female Savannah Sparrows (<em>Passerculus sandwichensis</em>, n = 60), and Bobolinks, (<em>Dolichonyx oryzivorus</em>, n = 75) breeding in managed hayfields and pastures in Shelburne and Hinesburg, Vermont, USA. Female Savannah Sparrows (age 1 to 6 years) showed evidence of reproductive senescence with the number of young fledged peaking at 2 years of age and declining in older age classes. Additionally, daily nest survival was strongly and negatively affected by female age. The effect of age on Bobolink reproductive performance was weak. We found an increase in the number of eggs laid from 1 to 2 years of age, no age effect on number of nest attempts or number of young fledged, and a weak, negative effect of age on daily nest survival. We found no support for an effect of grassland management treatment on daily nest survival, which may have been a result of unequal distribution of nesting attempts across treatment types. However, species-specific responses to hay harvest may have affected the relationship between age and reproductive performance. Savannah Sparrows renest rapidly and frequently after nest loss due to haying, which may constrain long-term investment in reproduction. In this highly managed system, older females may allocate less energy toward reproduction than younger females, potentially shifting those resources to behaviors that support annual survival. By contrast, Bobolinks may not invest as heavily in reproduction, generally renesting only once after nest failure and have a truncated breeding season because of their long fall migration to South America. Consequently, their reproductive success may not vary as strongly with age.

Diverse demographic factors influence apparent juvenile survival in a migratory songbird

AbstractTo better understand the dynamics of avian populations and their role in population trends, we require an in‐depth understanding of the factors influencing the survival of adults and juveniles. However, assessing survival in juveniles is often challenging, especially in small, migratory species where individuals typically disperse from the study area and are not available for recapture in subsequent years. Bobolinks (Dolichonyx oryzivorus) are a long‐distance migrant that exhibits natal philopatry in at least one population, allowing for more comprehensive juvenile survival analyses than in many other long‐distance avian migrants. Using a 17‐yr dataset from two sites representing a Vermont population of Bobolinks, we used Program MARK to assess factors influencing apparent juvenile survival, including factors related to nesting timing, nest attempt number, the philopatric behaviors of relatives, body mass, brood size, and agricultural management scheme. Our top models indicated that nest attempt number and whether or not a nest mate also survived and returned to breed locally were important factors explaining variation in apparent survival in juvenile Bobolinks. Specifically, juveniles from first nest attempts that fledged earlier in the season, with siblings that did not survive and return to breed locally, showed higher apparent survival. Factors such as site and the philopatric behavior of females associated with nests also appeared in top‐ranking models, while factors such as body mass and brood size did not. These results indicate the importance of providing high‐quality breeding habitat to birds early in the season when juvenile survival is greatest and indicate that individuals may be utilizing inbreeding avoidance strategies. These results provide new insight into the ecological and agricultural management factors influencing survival in migratory species that use managed habitats and underscore the importance of integrating juvenile survival data into current management schemes to better support this and other declining species.

Bobolink (Dolichonyx oryzivorus) Declines Follow Bison (Bison bison) Reintroduction on Private Conservation Grasslands.

Simple SummaryNorth American grassland birds evolved with American bison (Bison bison), until overhunting drove bison to near-extinction > 150 years ago. Bison have now been reintroduced to many areas that provide important nesting habitat for grassland birds, which are now among the most rapidly declining birds in North America. However, little is known about bison interactions with birds such as Bobolinks (Dolichonyx oryzivorus), obligate grassland nesting songbirds of conservation concern. Using data collected over an 18-year period, we assessed the effects of bison reintroduction, together with other land management and climate factors, on Bobolinks in a private conservation area comprising 24 km2 of native grasslands in the North American Great Plains. In grasslands where bison were reintroduced, Bobolink abundance (adult numbers) declined by 62%, and productivity (juvenile numbers) declined by 84%. By contrast, Bobolink populations remained stable over the same time period in adjacent grasslands where bison were not reintroduced. Bobolink abundance and productivity increased in years following warmer and wetter winters, but nevertheless declined over time in grasslands where the bison population doubled. Where bison are reintroduced and confined in high densities, overgrazing, trampling, and related impacts may drive severe declines in Bobolinks and other grassland birds of conservation concern.Among the most rapidly declining birds in continental North America, grassland birds evolved with American bison (Bison bison) until bison nearly became extinct due to overhunting. Bison populations have subsequently rebounded due to reintroductions on conservation lands, but the impacts of bison on grassland nesting birds remain largely unknown. We investigated how bison reintroduction, together with other land management and climate factors, affected breeding populations of a grassland bird species of conservation concern, the Bobolink (Dolichonyx oryzivorus). We quantified population changes in Bobolinks over an 18-year period in conservation grasslands where bison were reintroduced, compared with adjacent grasslands grazed by cattle and where hay was harvested after the bird breeding season. Four years after bison reintroduction, the bison population in the study area had doubled, while Bobolink abundance declined 62% and productivity declined 84%. Our findings suggest that bison reintroduction as a conservation strategy may be counterproductive in grassland fragments where overgrazing, trampling, and other negative impacts drive declines in grassland breeding birds. Where bird conservation is an objective, small grassland reserves may therefore be inappropriate sites for bison reintroduction. To maximize conservation benefits to birds, land managers should prioritize protecting grassland birds from disturbance during the bird breeding season.

Differential effects of policy-based management on obligate and facultative grassland birds

Policy-driven conservation on private lands, such as the U.S. Farm Bill’s Conservation Reserve Program (CRP), provides crucial habitat for consistently declining populations of grassland birds. In 2004, new CRP enrollments were required to be managed to floristically diversify old grass-dominated fields and provide early-successional habitat. Obligate and facultative grassland birds of varying conservation importance, along with the entire avian community, has received limited research attention within this applied management context. Moreover, multiple parameters (e.g. nest survival and adult density) – opposed to single parameter studies – need to be investigated simultaneously to better understand drivers of avian population dynamics associated with management. Using a combination of graphical and model selection approaches we addressed these gaps focusing on four main questions: 1) How does abundance and richness of various grassland bird community designations respond to broad (e.g. grass type) and specific (control, disking, herbicidal spray, and spray/interseeding) management treatments?; 2) How do grassland birds of conservation concern and economic importance collectively respond to management?; 3) Are various response parameters, including nesting parameters, consistent or decoupled across facultative and obligate species?; and 4) Is there a best management treatment to recommend? Overall, compared to non-native grass (smooth brome [Bromus inermis]) dominated fields, native fields had a greater number of avian species and number of individuals with higher and lower cumulative management, respectively. Facultative grassland species were mostly driving this trend and likely utilizing native fields that tended to have more vertical vegetation structure and forb diversity compared to brome fields. Grassland obligates with higher Conservation Values, such as bobolinks (Dolichonyx oryzivorus), however, were most abundant and species-rich on unmanaged brome fields compared to native fields. Response parameter decoupling was not readily apparent from our comprehensive modeling analysis of both adult survey and nesting data; however, nest survival was generally higher on native fields for eastern meadowlarks (Sturnella magna), an obligate, yet adult densities for meadowlarks were greater on unmanaged brome fields. Overall, pinpointing a specific mid-contract management practice for CRP that has benefits for all grassland birds remains challenging due to species-specific habitat requirements. However, it appeared the moderate effects of light strip-disking on vegetation may present a good management option for landowners because this treatment may be beneficial across multiple species of grassland birds and would also limit the impact of management to obligates utilizing unmanaged brome fields while also improving the avian Conservation Value of native fields.

Agriculture is adapting to phenological shifts caused by climate change, but grassland songbirds are not.

Migratory birds time their migration based on cues that signal resource availability for reproduction. However, with climate change, the timing of seasonal events may shift, potentially inhibiting the ability of some species to use them as accurate cues for migration. We studied the relationship between phenological shifts and reproduction by long‐ and short‐distance migratory songbirds—Bobolinks (Dolichonyx oryzivorus) and Savannah Sparrows (Passerculus sandwichensis). Our study population breeds in hayfields and pastures in Vermont, USA, where farmers are also changing management activities in response to climate change. From 2002 to 2019, we monitored nest initiation dates to quantify correlations with environmental factors and the timing of nest initiation. We collected historical and projected precipitation and temperature data for the breeding grounds, and their respective wintering and stopover sites, the North Atlantic Oscillation (NAO) and the El Niño Southern Oscillation (ENSO). We predicted that winter conditions experienced by the short‐distance migrant, the Savannah Sparrow, but not the long‐distance migrant, the Bobolink, would explain the timing and success of nesting, however that this timing would be misaligned with changes in agricultural practices by hay farmers. Nest initiation dates did not show significant directional change for either species, but did vary among years. Interannual variation in Savannah Sparrow nest initiation dates was best explained by the interaction between precipitation on the breeding grounds and average wintering site (Wilmington, North Carolina). For Bobolinks, interannual variation in nest initiation dates was best explained by the interaction between breeding ground precipitation and average temperature in their fall stopover site (Barquisimieto, Venezuela). However, first haying dates in Vermont advanced by ~10 days over 18 years. These results suggest that the conflict between the timing of hay harvests and grassland songbird reproduction will increase, further threatening population processes for these species, as early harvests notably decrease annual productivity.

Diel patterns of predation and fledging at nests of four species of grassland songbirds.

Although it is common for nestlings to exhibit a strong bias for fledging in the morning, the mechanisms underlying this behavior are not well understood. Avoiding predation risk has been proposed as a likely mechanism by a number of researchers. We used video surveillance records from studies of grassland birds nesting in North Dakota, Minnesota, and Wisconsin to determine the diel pattern of nest predation and fledging patterns of four ground‐nesting obligate grassland passerines (Grasshopper Sparrow (Ammodramus savannarum), Savannah Sparrow (Passerculus sandwichensis), Bobolink (Dolichonyx oryzivorus), and Eastern Meadowlark (Sturnella magna)). We used the nest predation pattern as a surrogate for predation activity to test whether nestlings minimized predation risk by avoiding fledging when predation activity was high and preferentially fledging when predation risk was low. Predation activity was significantly lower starting 3 hr before sunrise and ending 3 hr after sunrise, followed by a transition to a period of significantly higher activity lasting for 4 hr, before declining to an average activity level for the rest of the diel period. There was little evidence that the four grassland bird species avoided fledging during the high‐risk period and Savannah Sparrow fledged at higher rates during that period. All four species had hours during the low‐risk period where they fledged at higher rates, but only Grasshopper Sparrow fledged preferentially during that period. Bobolink and Eastern Meadowlark had multiple hours with high fledging rates throughout the daytime period, resulting in no relationship between probability of fledging and predation risk. Given the species variability in fledging pattern seen in our study, it is unlikely that there is a universal response to any driver that affects time of fledging. Further study is needed to understand the complex interplay between species ecology and drivers such as physiology, energetics, and predation in affecting grassland bird fledging behavior.

Mixed consequences of divorce on reproductive success of songbirds nesting in agricultural hayfields

Agricultural management, particularly haying, can cause synchronous nest failure of ground-nesting songbirds. As a consequence, these birds may subsequently renest and choose a new social mate (divorce). This study (1) quantified within-year and between-year divorce rates of grassland songbirds, and (2) determined if divorce rates differed after haying or predation-caused nest failure, and if so, whether divorce influenced reproductive success. From 2002 to 2017, we monitored 121 Bobolink (Dolichonyx oryzivorus) pairs and 436 Savannah Sparrow (Passerculus sandwichensis) pairs in an agricultural region of Vermont, USA. Within-year and between-year divorce rates were 0–84.9% for Bobolinks and 17–69.1% for Savannah Sparrows. Between years, Bobolinks, but not Savannah Sparrows, were more likely to divorce after nest failure, but haying did not influence divorce rates. Within years, Savannah Sparrows were more likely to divorce after nest failure, but as with Bobolinks, divorce rates in Savannah Sparrows were not different between nests that failed due to haying or predation. Across all Savannah Sparrow renests, divorce had no influence on the number of young fledged per female. However, between years, female Bobolinks that divorced fledged more young in their first attempt while those that did not divorce fledged more young in their second attempt. This study showed that pairing decisions were not differentially affected by cause of nest failure. Further, we identified no reproductive benefit to divorce. Our results indicate no adaptive benefit and potentially a significant reproductive cost to divorce, and that these effects vary between species.

Breeding Bird Occurrence Across a Gradient of Graminoid- to Shrub-Dominated Fens and Fire Histories

Population declines of birds affiliated with grasslands and grass-shrub habitats have been identified as a critical conservation concern. The effects of woody encroachment into grassland-dominated systems, which may contribute to species declines, has been examined mainly in upland systems. We examined occurrence of bird species across a gradient of graminoid- to shrub-dominated wetlands in the Upper Peninsula of Michigan and describe the habitat characteristics associated with their probability of occurrence at segment (100 × 100 m) and landscape (200 m buffer) scales. Because fire can suppress woody encroachment, we also examined the role of fire history, extending from 50 y on birds and habitat characteristics. We focused on seven species closely affiliated with grassland and grass-shrub habitats, but also found in wetlands: Sedge Wren (Asio flammeus), LeConte's Sparrow (Ammodramus leconteii), Savannah Sparrow (Passerculus sandwichensis), Bobolink (Dolichonyx oryzivorus), Common Yellowthroat (Geothlypis trichas), Swamp Sparrow (Melospiza georgiana), and Alder Flycatcher (Empidonax alnorum). We used nonparametric, multiplicative regression models to relate habitat variables and fire history to probability of species occurrence. Unlike studies in upland grasslands, none of the top models included measures of litter or graminoid height, and the highest probability of occurrence often was where graminoid cover was at intermediate rather than highest levels. Measures of woody cover or structure were important to all seven species modeled. We observed few clear differences in habitat metrics across fire history categories beyond the first year of burning. Years since last burned was in the best model for four of the seven species, despite high variability of habitat metrics within fire history categories; those species were more likely to occur in segments burned 15–19 y earlier. Infrequent light- to moderate-severity fires in fens had little effect on focal species occurrence beyond the first year after burning and little long-term effect to suppress woody cover.

Invention: The Raven and the Bobolink: An American Fable

Invention: The Raven and the Bobolink: An American Fable

Determining When Bobolink Finish Breeding to Time Agricultural Activity in Nesting Refuges

ABSTRACTConservation actions are ongoing for the federally and provincially threatened bobolink (Dolichonyx oryzivorus) in Ontario, Canada because of population declines. One conservation action being implemented in agricultural grasslands is the delay of hay harvesting and livestock grazing until 15 July, a general guideline for when bobolink finish breeding. Efficient methods to assess when breeding ceases could benefit bobolink and farmers engaged in conservation by ensuring nesting is finished before agricultural activity occurs and enabling agricultural activity earlier when breeding is finished before 15 July. We conducted field surveys to assess if low‐intensity surveys (i.e., transect surveys, point counts, roadside counts) could accurately detect when bobolink finish breeding compared to intensive monitoring (i.e., spot mapping and nest monitoring). We monitored 29 pastures in 2017 in eastern Ontario and 9 hay fields, 10 restored grasslands, and 6 fallow fields in 2018 in southern Ontario. The date breeding finished varied across fields in 2017 from 13 June to 29 July and in 2018 from 24 June to 30 July, based on spot mapping and nest monitoring. Transect surveys and point counts were good predictors of breeding in a field, as confirmed through spot mapping and nest monitoring, based on generalized linear mixed models. We recommend using transect surveys or point counts as an efficient field method to assess when bobolink finish breeding in a field targeted for bobolink conservation. Our results suggest that 2 consecutive visits that fail to detect evidence of breeding in early July are needed to reasonably infer that breeding has likely finished, leaving a small probability (i.e., &lt;0.01) that breeding may still be occurring. Determining when bobolink finish breeding in fields intended to provide nesting refuges can help maximize conservation benefits and minimize negative effects on agricultural production. © 2020 The Wildlife Society.

A 137-Year History of the Summer Avian Community at the Winous Point Marsh, Port Clinton, Ohio, USA

The Winous Point Marsh Conservancy and the Winous Point Shooting Club, with landholdings in both Sandusky and Ottawa Counties, Ohio, has completed a survey of the summer resident bird population on the property 4 times spanning 137 years. Although achieving a true census is unrealistic, these surveys have provided a unique, long-term history of changes in the avian community in northwest Ohio since the 1880s. Surveys were completed in 1880, 1930, 1960, and 2017. Draining and deforestation of the wetlands in northwest Ohio, by the late 1870s, resulted in the loss of many forested-wetland dependent species such as Blue-gray Gnatcatcher (Polioptila caerulea), Solitary Sandpiper (Tringa solitaria), and Northern Waterthrush (Parkesia noveboracensis) after the 1880 survey. Intensification of agricultural practices after the 1930 survey likely resulted in the loss of the early successional habitat that was associated with smaller, less intensive, agricultural practices and consequently the loss of many grassland nesting species such as Bobolink (Dolichonyx oryzivorus), Eastern Meadowlark (Sturnella magna), Northern Bobwhite (Colinus virginianus), Blue-winged Teal (Anas discors), Northern Pintail (Anas acuta), and Northern Shoveler (Anas clypeata). Several new species were documented during the 2017 survey including Osprey (Pandion haliaetus), Sandhill Crane (Antigone canadensis), Trumpeter Swan (Cygnus buccinator), and American White Pelican (Pelecanus erythrorhynchos). This long-term dataset provides a unique opportunity to investigate the avian immigration, extirpation, and recolonization of a specific site over the past 137 years, providing insight into how landscape-level habitat changes affected the avian community.

Diet of the Bobolink (Dolichonyx oryzivorus) in rice fields on its wintering grounds in Argentina

Winter diet of Bobolinks (Dolichonyx oryzivorus), a bird considered a pest of rice fields, is known to consist primarily of seeds. However, it is not yet possible to establish the extent to which non-rice plants and animal components contribute to its diet. To contribute to these issues, we studied the diet of the Bobolink found in rice fields on its wintering grounds in Santa Fe, Argentina, to provide information on (i) the composition of the diet and (ii) the relative importance of plant and animal components in the diet and of the different prey categories. We captured Bobolinks with mist nets and obtained samples of stomach contents by warm water and emetic-based regurgitation to determine the composition of the diet (n = 46 samples) and the importance of the different prey (n = 25 samples), mainly during March, just prior to northbound migration. We confirmed that the Bobolink’s diet in this region during this period is predominantly herbivorous (97%) and rice-based (55%), although it also consumes a large number of seeds of non-cultivated plants that represented 42% of the diet. Invertebrates, although of less importance than plant components (3%), had been consumed by 97% of captured individuais. Our results document the importance of non-cultivated plants and animal prey in the diet of Bobolinks in addition to rice.