Eric K. Bollinger

Reproductive Correlates of Breeding‐Site Fidelity in Bobolinks (Dolichonyx Oryzivorus)

To investigate the relationship between reproductive success (RS) and breeding—site fidelity in a transequatorial migrant, we studied two populations of marked Bobolinks (Dolichonyx oryzivorus) in upstate New York during 1982—1985. At these sites, 44% of the males and 25% of the females resident in one year returned in one or more subsequent years. There were more nests built, eggs laid, eggs hatched, and young fledged in territories of returning males in this polygynous species than in territories of males that did not return in subsequent years (P < .04). For females that returned, the number of eggs hatched, young fledged, young fledged on last nest attempt, and young fledged per egg laid were higher than for females that did not return (P < .02). Discriminant function analysis and data from 1982—1984 were used to predict correctly the return behavior of 30 to 42 individuals (sexes combined) in 1985, based on their reproductive success (RS) in 1984 (P < .01). Using data on RS and return rate for all years, the best single—variable model for males based on the number of young fledged from each territory classified correctly 59 of 85 individuals (69%) as returning or not (P < .005). The best single—variable model for females based on the number of yound fledged on their last nest attempt classified correctly 61 of 86 individuals (71%; P < .005). Using all data for 1982—1985, sex—specific models that included only whether an individual fledged one or more young classified correctly the same proportion as the best single—variable models above. However, among males that fledged one or more young, those that returned had fledged significantly more young the previous year than those that did not return (P < 0.5). Not all individuals that failed to return were dead, because five individuals that did not return to our study sites were captured in a subsequent year at another site. We concluded that male and female Bobolinks used information on their breeding success in one year to influence their choice of breeding site in the next year.

Predation Rates on Real and Artificial Nests of Grassland Birds

Abstract We estimated nesting success at real and artificial nests of grassland birds to test the influence of nest type, nest position, and egg size on predation rates. We distributed wicker nests and realistic woven-grass nests baited with a clay egg and either a Northern Bobwhite (Colinus virginianus) egg or a House Sparrow (Passer domesticus) egg in four grasslands that were part of the Conservation Reserve Program in east-central Illinois. Nesting success averaged 86.5% for 12 days of exposure for artificial nests. For real nests, nesting success was markedly lower, averaging 39% over the entire nesting cycle and 59% during approximately 12 days of incubation. Wicker nests were depredated more often than woven-grass artificial nests (18% vs. 8%), and nests baited with House Sparrow eggs were depredated more often than nests baited with Northern Bobwhite eggs (22% vs. 9%). Elevated and ground nests were depredated at the same rate. Patterns of nest predation on wicker nests were markedly different from depredation patterns on real nests over time and among fields. In contrast, patterns of nest predation on realistic woven-grass nests corresponded much more closely with predation rates of real nests over time and among fields. We suggest that future artificial nest studies use nests and eggs that mimic as closely as possible the real nests and eggs of target species. Use of unrealistic artificial nests and eggs, at least in grasslands, may result in patterns of predation that do not accurately reflect those of real nests. Artificial nests of any type appear to underestimate predation rates on nests of grassland birds, possibly because of a lack of snake predation on artificial nests.

Explanations for the infrequent cowbird parasitism on Common Grackles

We determined the factors responsible for the lack of parasitism on Common Grackles (Quiscalus quiscula) by Brown-headed Cowbirds (Molothrus ater). We found no evidence of parasitism on the 401 grackle nests we monitored in east-central Illinois. By the time cowbirds began laying eggs, 88.5% of all grackle nests were beyond the point of successful parasitism. Grackles rejected cowbird eggs more frequently during the prelaying stage of the nesting cycle (38.2%) compared to later stages (12.3%). Thirty-three cowbird eggs and nestlings were cross-fostered into grackle nests. Data were collected on 15 cowbird nestlings, of which three fledged. The cross-fostered cowbird eggs that did not hatch appeared to have been incubated ineffectively. These eggs were in clutches that contained four to six eggs, whereas the cowbird eggs that hatched were in clutches of three eggs or less. Grackles also responded more aggressively toward female cowbird models than to Fox Sparrow (Passerella iliaca) models in five of seven response categories. Cowbirds avoid parasitizing grackles even though the opportunity existed. Nest abandonment and infestation of grackle nests with ectoparasitic mites may decrease the suitability of grackles as hosts; however the primary reason for the infrequent cowbird parasitism on grackles appears to be past rejection behavior. Grackles likely rejected cowbird eggs at a higher frequency in the past and as a consequence grackles were avoided by cowbirds. Rejection apparently decreased in the absence of parasitism due to the high degree of intraclutch egg variability exhibited by grackles which would increase the chances of them mistakenly rejecting their own discordant eggs.

Inbreeding Avoidance Increases Dispersal Movements of the Meadow Vole

This study tested whether inbreeding avoidance could influence the frequency and timing of dispersal movements in a small microtine rodent, the meadow vole (Microtus pennsylvanicus). Meadow voles released into experimental grassland plots with siblings were more likely to disperse from these plots than were voles released into similar plots with nonsiblings. Furthermore, voles that dispersed from siblings groups did so sooner than dispersing voles from nonsiblings groups. Voles released with nonsiblings were recaptured within the plots for longer periods than were voles from siblings groups. Males from both groups remained within the plots for shorter times than did females, but the degree of this sex bias was greater for siblings groups. Thus, it appears that inbreeding avoidance can influence dispersal movements of the meadow vole and may be partially responsible for patterns of male—biased dispersal in at least some mammals.

RESPONSES OF NESTING BOBOLINKS (DOLICHONYX ORYZIVORUS) TO HABITAT EDGES

Abstract Avoidance of habitat edges may be contributing to reduced densities of grass-land birds in small habitat patches. Nest densities for grassland-nesting Bobolinks (Dolichonyx oryzivorus) were much lower than expected within 25 m of forest edges at three sites in New York, and that pattern (“edge avoidance”) extended to 100 m at one site. Nests located within 50 m of forest or wooded hedgerow edges had lower daily survival rates, compared with nests ≥100 m from any habitat edge. Bobolinks tended to move away from forest edges when renesting after nest failure; that pattern was especially evident in females that placed their first nest within 50 m of a forest or wooded hedgerow edge. Second nests of all seven of those females were farther from that edge type than their first nests. However, nest placement in relation to wooded edges did not vary significantly between years for those philopatric females nesting at our study sites for more than one year. Bobolinks also avoided nesting near road edges, even though nest survival rates were not lower near that edge type. However, Bobolinks did not appear to avoid nesting near edges adjacent to old fields or pastures. Nest survival near those edge types was higher than near wooded edges and similar to or higher than survival of nests ≥100 m from any edge. Thus, responses of Bobolinks to habitat edges were inconsistent, and nest success was dependent on type of edge.

Renesting Decisions and Annual Fecundity of Female Dickcissels (Spiza americana) in Illinois

Abstract Renesting decisions and annual fecundity are crucial for interpreting other demographic information, yet are infrequently reported. We used radiotelemetry to monitor female Dickcissels (Spiza americana) throughout the 1999 and 2000 breeding seasons in southeastern Illinois. Overall fecundity (regardless of whether females remained in the study area throughout the breeding season) was 0.61 ± 0.13 female fledglings per year. Of females that remained within the study area, 94% fledged young (1.25 ± 0.15 female fledglings per year). Most females (62%) that experienced nest failure emigrated from the study area (moved >10 km) in 2.8 ± 0.6 days; others (36%) initiated subsequent nests in 8.5 ± 0.8 days. After fledging ≥1 young, 95% of females ceased breeding for the season. Successful and failed nest sites were indistinguishable on the basis of vegetative characteristics. Moreover, replacement nests had similar vegetative characteristics and were similar distances from habitat edges, compared with initial nests, which suggests that female Dickcissels do not or cannot “improve” nest-site characteristics in response to nest failure. We observed two behaviors unusual in female Dickcissels: one bird that fledged two broods in one season, and the return of five females banded in 1999 to the study site in 2000.

Rejection of Cowbird Eggs by Mourning Doves: A Manifestation of Nest Usurpation? Brian D. Peer and Eric K. Bollinger

MCKELVEY, R. M. BOUSFIELD, A. REED, V. V. BARANYUK, AND R. CANNIFF. 1989. Preliminary results of the Lesser Snow Goose collaring program on the Alaksen National Wildlife Refuge. CWS Progress Notes No. 183. MINEEV, g. 1. 1946. Wrangel Island. Glavsevmorput Publications, Moscow. NEI, M. 1977. F-statistic and analysis of gene diversity in subdivided populations. Annals of Human Genetics 41:225-233.

Factors influencing blackbird damage to field corn

The relative importance of 12 variables in explaining the variation in blackbird damage among 50 cornfields located 2-7 km from a large blackbird roost in Cayuga County, New York, was assessed. Date of silking was the most important predictor of bird damage to corn; earlier maturing fields received greater damage. A fields peak population of northern corn rootworm beetles (Diabrotica longicornis) was the second most important variable and was also negatively correlated with bird damage. Other variables of lesser importance were the extent to which a field was bordered by woods and hedgerows and the fields weediness (both positively correlated with damage). Husk extension past the tip of a corn ear was always negatively correlated with blackbird damage within a given field that received higher amounts of bird damage. Because this variable was unimportant in explaining variation in damage among fields, however, we feel that recommending the use of corn hybrids whose bird-resistance is based primarily on husk extension is unwarranted. J. WILDL. MANAGE. 49(4):1109-1115 On a continent-wide basis, blackbird damage to corn is not a serious problem. Less than 1% of the total crop is lost to blackbirds (primarily red-winged blackbirds, Agelaius phoeniceus) in both the United States (Stone et al. 1972) and Canada (Tyler and Kannenberg 1980), whereas insects, weeds, fungi, and diseases combine to reduce potential yield by an average of at least 20% (Jugenheimer 1976:261, Pimental 1976, McEwen 1978, Dolbeer 1980). Blackbird damage to corn, however, is not evenly distributed. Whereas most farmers receive little or no damage, a small proportion of growers suffer severe economic losses (Dolbeer 1981). Although on a regional scale, most of this major bird damage occurs in cornfields located near autumn blackbird roosts (Cardinell and Hayne 1945, Dyer 1967, Martin 1977, Dolbeer 1980), damage levels vary widely even among fields located

Effect of parasite-to-host egg ratio on egg rejection by a Brown-headed Cowbird host

ABSTRACT American Robins (Turdus migratorius) typically eject parasitic Brown-headed Cowbird (Molothrus ater) eggs from their nests. In order to successfully remove parasitic eggs, robins must first differentiate between their eggs and foreign eggs, and then remove the foreign egg(s). Our primary objectives were to determine (1) whether the robins reject cowbird eggs because they are in the minority (“discordancy hypothesis”) or because robins have learned the appearance of their own eggs regardless of whether they form the majority of eggs in the nest (“true egg recognition hypothesis”); and (2) whether the robins ability to recognize its eggs and reject parasitic eggs was affected by the parasite-to-host egg ratio. We added artificial cowbird eggs to robin nests to create 3 treatments: (1) a majority of robin eggs, (2) an equal number of robin and cowbird eggs, and (3) a majority of cowbird eggs. Parasite-to-host egg ratios were between 1:3 and 3:1. Robins ejected all cowbird eggs at 88% of nests (51 of 58). The frequency of ejection did not differ between the 3 treatments, indicating that robins typically recognized their eggs regardless of whether they were the majority egg type, providing strong support for the true egg recognition hypothesis. However, the risk of ejection for the artificial cowbird eggs was greater as the ratio of cowbird to host eggs increased, which suggests that robins respond adaptively to the increased fitness costs of multiple parasitism. Finally, the risk of ejection of our artificial cowbird eggs was greater later in the nesting season. Because many individuals were exposed to their eggs for the first time early in the season, this result suggests that robins learn to recognize their eggs during their initial nesting attempt.

Genetic Evidence of Isolation by Distance and Impact of Impoundments on Genetic Diversity of Riverine Channel Catfish

AbstractThis study used microsatellite loci to provide evidence of isolation by distance and an effect of artificial impoundments on the genetic diversity of Channel Catfish Ictalurus punctatus from the Wabash and Ohio rivers. The Wabash River is the longest free-flowing river east of the Mississippi River in the USA, and the Ohio River is highly impounded, yet both rivers support large Channel Catfish fisheries. There was a significant positive relationship between genetic differentiation and geographic distance indicating isolation by distance. Clustering with the programs, STRUCTURE and GENELAND, and principal component analysis revealed multiple genetic clusters, and several sites had results consistent with adults existing as mixtures of genetic groups. These results suggest that the rate of straying among reproductive sites or dispersal is dependent on geographic distance. Channel Catfish from the unimpounded Wabash River had higher genetic diversity (Ho and He) than that from the impounded Ohio Riv...