IOWA AUDUBON IOWA IBA EDUCATION INITIATIVE PART 4: SPECIES ACCOUNTS

STATUS: HIGH Bobolink CONSERVATION PRIORITY IN IOWA Dolichonyx oryzivorus

Introduction The Bobolink is a species that has long been familiar to many Iowa landowners, and it is one of the most distinctive birds of Iowa grasslands. During spring and summer the brightly colored male is easily recognized with overall black appearance, large patches of white on wings and down middle of back, and tawny yellow nape, or back of neck. Males are especially conspicuous during the nesting season as they perch high on plant stems and sing a long bubbly song during aerial displays – in helicopter-like flight – over the grassland. Females are duller colored and more secretive. Bobolinks have one of the longest migration journeys of any Iowa songbird, wintering on grasslands in southern South America. One female known to be at least nine years old presumably made this trip annually, a total distance equal to traveling 4.5 times around the earth at the equator! Bobolinks have been shot as agricultural pests in the southern United States, trapped and sold as pets in Argentina, and collected as food in Jamaica. The species is not as abundant as it was several decades ago, primarily because of changing land-use practices here where it reproduces, especially detrimental are the decline of meadows and hay fields. The combination of losses on the wintering grounds and destruction of many of the grasslands in Iowa has led to an overall decline in their numbers in Iowa.

LINK TO IOWA IBA: BOBOLINK IOWA AUDUBON IOWA IBA EDUCATION INITIATIVE PART 4: SPECIES ACCOUNTS

Habitat Preferences Bobolinks feed primarily as they walk slowly on the ground or as they ascend into lower The Bobolink is a species of the Tallgrass levels of vegetation. When foraging on Prairie Ecosystem. It prefers habitat with seeds, they often perch near the top of moderate to tall vegetation, moderate to vegetation to extract and ingest seeds. dense vegetation, and moderately deep Foraging occurs throughout daylight hours. litter without the presence of woody During the breeding season, they are vegetation. Bobolinks originally nested in solitary foragers. In post-fledging groups on tall-grass or mixed-grass prairie. Most of nesting fields and during migration and this habitat came under intense agricultural winter, Bobolinks join intra-specific flocks, pressure more than a century ago. which have highly social feeding behavior. Presently in Iowa this species is found in old fields, pastures, wet meadows, and Breeding Biology prairie. It seems to especially use old In three well-studied populations, the hayfields that are comprised of a mixture of majority of males that establish initial grasses and broad-leaved forbs. Population territories normally arrive suddenly on density is significantly higher in fields with breeding grounds in early May, and depart relatively low amounts of total vegetative slowly from July to early September. Older cover, low alfalfa cover, and low total males generally precede yearlings by legume cover but with high litter cover and several days in spring. Females normally high grass-to-legume ratios relative to other begin arriving 4 to 8 days after the initial nearby fields. group of territorial males. Earliest returning Bobolinks also breed in habitats similar to females also tend to be the oldest. grass-sedge fields along river bottomland This species tends to return to areas where habitat, and sometimes in irrigated it has nested successfully before, and both meadows. sexes exhibit high breeding-site fidelity. Feeding Habits Bobolinks are widespread and fairly evenly distributed in Iowa, and tend to occur In Iowa, during nesting, adult Bobolink feed wherever suitable grassland habitat is on weed seeds, a variety of larval and adult provided. insects, spiders, and harvestmen. The Females returning to the same breeding young are fed exclusively invertebrates. In habitat often settle with a male within hours migration this species feeds on wild and of returning, occasionally re-pairing with domesticated rice, oats, other small grains, same male of a previous year. During early weed seeds, and occasionally on insects. courtship phases, males devote complete Bobolinks forage on seeds at the tops of courtship attention to the female. After a forbs interspersed within expanses of second day of courtship, and always by first grasses or sedges. They glean insects and day of the copulation period, males spiders from mid-growth and bases of attempts to attract unpaired females. This forbs, grasses, and sedges. The preferred species is polygynous with the males foraging height is 2 to 6 inches above forming pair bonds with more than one ground. Occasionally foraging is for female. Polygynous males often pair with invertebrates in trees and shrubs adjacent second mates 3 to 8 days after initial to or within nesting sites. Providing pairing occurs. Pair formation within a grassland habitats for feeding is population is highly synchronous, with most recommended. males that are successful in becoming

LINK TO IOWA IBA: BOBOLINK IOWA AUDUBON IOWA IBA EDUCATION INITIATIVE PART 4: SPECIES ACCOUNTS paired, attracting their first females within a Undisturbed Bobolink young leave the nest few days. on day 10 or 11. They move as much as Nest construction takes place in the second 200 feet the first day out of nest, thus the or third week of May and is completed in 1 size of overall grassland habitats is to 2 days. Food abundance may influence important. Adults divide labor of feeding, timing of nesting events. One egg is laid each parent concentrating on specific each day, starting within 1 to 2 days of nest fledglings. completion. There are usually 5 to 6 eggs Until flight capability is developed at laid, but the number may vary from 3 to 7. approximately 13 days of age, birds Incubation is by the female only. An generally remain in thick vegetation, relying average incubation period is approximately on cryptic coloration for concealment. By 16 12 days. Undisturbed young fledge 10 to 11 days of age, the young are capable of days after hatching. sustained flights of over 500 feet. Within The norm is one brood per season. flocks, adults continue feeding their own Bobolink nests tend to be located in wet young, for at least 28 days after birds leave habitats, transitional between drier soils and the nest. Flocks leave breeding vicinities areas providing poor drainage. Nests are soon after immatures gain independence. always on the ground, and often at base of Concerns and Limiting Factors a large forb. Shading and temperature Breeding Bird Survey data for 1966-2004 modulation at the nest appear to be show a significant decreasing trend of – important to nesting females. 1.7%/year over the Bobolinkʼs range and – Nest construction activity is often intensive. 4.1%/year within Iowa during that same It is important to note that nests discovered period. In the Midwest, the primary reason early in construction are often immediately for this population decline is habitat loss. abandoned. For this reason, great care Bobolinks appear to be area specific, should be taken when walking through preferring large grassland areas over grasslands that support Bobolinks from mid smaller habitats. One researcher reported to late-May, and perhaps later. Surveys for that the minimum area on which Bobolinks IBA purposes can usually be accomplished were found was 25 to 75 acres in prairie effectively from a distance, and this is partly fragments, and Bobolink abundance in because singing males are so obvious these fragments was positively related to during this time of year. the size of the area. After approximately 12 days of incubation Research has shown that Bobolinks prefer and 4 days of brooding after hatching, hayfields with high grass-to-forb ratios and brooding frequency declines markedly and avoid hayfields with high legume-to-grass temperature regulation probably ratios. A serious downside for Bobolinks commences about this time. Young have nesting in hayfields is that mowing left the nest and running capability develops accounted for significant nest losses. by 7 days after hatching. The presence of woody vegetation within Feeding begins within 1 hour after first and along the edge of grasslands can have nestling hatches; and continues until a negative impact on Bobolinks. Nest fledglings become independent. Nestlings depredation and Brown-headed Cowbird are fed exclusively invertebrates. Brood brood parasitism increase near woody parasitism by Brown-headed Cowbirds is edges, and nest depredation rates were known to occur, but is evidently not frequent.

LINK TO IOWA IBA: BOBOLINK IOWA AUDUBON IOWA IBA EDUCATION INITIATIVE PART 4: SPECIES ACCOUNTS lower in larger (325-1215 acre) grasslands, treated each year. In small, isolated than on smaller (40-80 acre) grasslands. grassland fragments, burning less than 50 Lower rates of nest depredation on to 60% of the total area at a time is Bobolink nests occurred in areas burned recommended. Mow or burn patches every within the last three years, where woody two to three years to prevent excessive vegetation and deep litter were reduced by encroachment of woody vegetation. fire. Nest productivity was highest and the To create Bobolink nesting habitat where probability of encountering Bobolinks was grazing occurs, grazing should be at also highest one year after burning. moderate levels to provide diverse grass Habitat Management heights and densities in areas where the average height of vegetation is 6 to 12 Recommendations inches. Also, graze using a rotational The combination of destruction, system of two or more grazing units. This fragmentation, and degradation of will increase the variation in grass heights grassland nesting habitats in the state has and densities within and between units. To led to an overall decline in Bobolink maintain plant vigor, do not graze warm- numbers over several decades of time. season grasses in tallgrass prairie to a The keys to Bobolink management are height of less than 10 inches during the providing large areas of suitable habitat growing season. (native and tame grasslands of moderate Nest disturbances during early stages of height and density, with high grass to forb incubation present serious problems for this ratios and adequate litter), controlling species. Females may abandon nests succession, and protecting nesting habitat during early incubation if nest is visited; but from disturbance during the breeding rarely abandons nest after day 3 of season. Avoid disturbing (e.g., haying, incubation. burning, moderately or heavily grazing) The primary disturbance to nesting sites is nesting habitat during the breeding season, hay-cropping. In one study, 100% of nests early May to early August. Treatments can with eggs or young nestlings affected by be done in early spring, several weeks prior mowing were abandoned or destroyed. to the arrival of adults on the breeding However, the proportion of young that were grounds in early May, or in the fall after the lost declined with increasing age of breeding season. nestlings. It is also recommended that habitat be Fields should be mowed annually to managed in patches larger than 25 to 75 maintain breeding habitat, but mowing acres, and woody edges are minimized should be delayed until at least late July or whenever possible to decrease Brown- early August in order to minimize negative headed Cowbird brood parasitism. impacts on fledglings. Later mowing would When managing prairie or old fields for be better, especially when re-nesting Bobolinks, a rotating treatment schedule on attempts are being made. several adjacent grassland fragments For general information about habitat should be used to make a variety of management for Bobolink, see the sections successional stages available. Burn within on Grassland Management for Birds. For areas that are at least 200 acres in total more specific details see Recommended size. A rotational burning system with Grassland Management Practices. Each of subunits of at least 75 acres in size, or these sections is found in Part 3. about 20 to 30% of the total area, can be

LINK TO IOWA IBA: BOBOLINK