Benjamin B. Steele

Age-specific nest-site preference and success in eiders

Variation in nest concealment is puzzling given the expected strong selection for safe nest sites. Selecting a concealed nest may decrease the risk of clutch predation but hinder parents from escaping predators, providing a possible solution to this paradox. Because the relative value of current versus future reproduction may vary with breeder age or state, nest concealment may also vary as a function of these attributes. We tested four predictions of the female and clutch safety trade-off hypothesis in eiders (Somateria mollissima): (1) nest concealment is negatively related to escape possibilities, (2) our capture rate of females is higher in covered nests, (3) egg predation is higher in open nests, and (4) overall nest success is unrelated to nest habitat. We also analysed nest microhabitat preferences and nest success relative to breeder age and body condition, controlling for nest spatial centrality. As expected, nest concealment and potential escape angle were negatively related, and capture by us, indicating female predation vulnerability, increased with nest cover. Clutch size was smaller in open nests, suggesting higher partial clutch predation, while it was larger among experienced and good-condition breeders. The probability of successful hatching was unrelated to nest habitat, positively associated with breeder experience, and negatively associated with hatching date. Experienced females selected more concealed and centrally located nests without sacrificing potential escape angles. The age-specific spatial distribution of nests on islands was unrelated to nest initiation dates, indicating no apparent competition. The age-specific preference of eiders for concealed nests may reflect declining reproductive value with age or confidence in surviving despite selecting a concealed nest. The apparently positive relationship between female age and survival and fecundity in eiders refutes the former alternative. Individual improvement in choosing safe nest sites, coupled with differential survival of individuals performing well, most likely explains age-specific nest-site preference and success.

Are bird-consumed fruits complementary resources ?

We conducted field experiments in 1994 and 1995 to determine whether fleshy fruits consumed by North American, migrant passerines are antagonistic, complementary, or perfectly substitutable resources. Joint consumption of resources that are antagonistic results in reduced fitness, whereas joint consumption of those that are complementary resources results in increased fitness, than would be predicted from consumption of a linearly weighted sum of the two (or more) resources. Joint consumption of perfectly substitutable resources results in fitness equal to that predicted by consumption of the linearly weighted sum of the resources. Of ten pairs of fruit species tested, eight exhibited resource complementarity (sign test, P < 0.05); however, the strength of complementarity varied among the species pairs. In the two comparisons in which evidence for complementarity was not found, most fruit consumption appeared to have been accomplished by seed predators rather than true frugivores (house finches, Carpodacus mexicanus, in one case, and eastern chipmunk, Tamias striatus, in a second). In a replication of the second comparison, most consumption of one fruit species was due to a flock of starlings (Sturnus vulgaris), a species lacking sucrase activity (which may help explain the result). We suggest that resource complementarity is generally common among fruits, which may help explain why so few frugivores are found to specialize on only a single or even a small number of fruit species. Resource complementarity has important implications for the ecological and evolutionary interactions of avian frugivores and fruit-producing plants. The biochemical and physiological bases of complementarity are unknown, but could involve nutrients, secondary metabolites/toxins, or both.

Habitat-specific clutch size and cost of incubation in eiders reconsidered

The energetic incubation constraint hypothesis (EICH) for clutch size states that birds breeding in poor habitat may free up resources for future reproduction by laying a smaller clutch. The eider (Somateria mollissima) is considered a candidate for supporting this hypothesis. Clutch size is smaller in exposed nests, presumably because of faster heat loss and higher incubation cost, and, hence, smaller optimal clutch size. However, an alternative explanation is partial predation: the first egg(s) are left unattended and vulnerable to predation, which may disproportionately affect exposed nests, so clutch size may be underestimated. We experimentally investigated whether predation on first-laid eggs in eiders depends on nest cover. We then re-evaluated how nesting habitat affects clutch size and incubation costs based on long-term data, accounting for confounding effects between habitat and individual quality. We also experimentally assessed adult survival costs of nesting in sheltered nests. The risk of egg predation in experimental nests decreased with cover. Confounding between individual and habitat quality is unlikely, as clutch size was also smaller in open nests within individuals, and early and late breeders had similar nest cover characteristics. A trade-off between clutch and female safety may explain nest cover variation, as the risk of female capture by us, mimicking predation on adults, increased with nest cover. Nest habitat had no effect on female hatching weight or weight loss, while lower temperature during incubation had an unanticipated positive relationship with hatching weight. There were no indications of elevated costs of incubating larger clutches, while clutch size and colony size were positively correlated, a pattern not predicted by the ‘energetic incubation constraint’ hypothesis. Differential partial clutch predation thus offers the more parsimonious explanation for clutch size variation among habitats in eiders, highlighting the need for caution when analysing fecundity and associated life-history parameters when habitat-specific rates of clutch predation occur.

Aggressive females seize central positions and show increased vigilance in brood-rearing coalitions of eiders

Decreased risk of predation is a key benefit of group living, and selfish herd theory predicts competition for the relative safety of central positions. Spatial position also affects behaviour, as individuals trade-off their feeding and vigilance to mitigate the risk of predation. Female eiders, Somateria mollissima, often pool their broods and share brood rearing, and anti-predatory vigilance is a core parental care activity. Females are assumed to trade-off vigilance and feeding, as efficient recovery of condition is crucial for energetically stressed postincubating females. Evidence shows that a females own ducklings are closer to her than unrelated young in amalgamated broods and that predation of ducklings by gulls is edge biased, so a females spatial position should correlate with the survival prospects of her brood. We identified determinants of female spatial position (aggression, structural size, body weight, age, clutch size) within multifemale brood-rearing coalitions, and explored whether spatial position affected female activities. Female aggression frequency was the only significant predictor of centrality in brood-rearing coalitions, and female age was positively associated with aggression. Investment in vigilance, but not investment in feeding, increased with spatial centrality; instead, central females devoted less time to other activities (resting, preening and moving). We conclude that central eider females do not need to trade-off vigilance and feeding. Heavy body weight did not guarantee a favourable position in brood-rearing coalitions, which may help explain our previous finding that female eiders in best body condition when their brood hatches tend their brood alone.

SITE FIDELITY AND EPHEMERAL HABITAT OCCUPANCY: NORTHERN WATERTHRUSH USE OF PUERTO RICAN BLACK MANGROVES DURING THE NONBREEDING SEASON

Abstract We studied the dispersion of Northern Waterthrushes (Seiurus novaboracensis) in southwestern Puerto Rico during four nonbreeding seasons, 1996–1999. Densities were high (up to 13 birds/ha) on a 3-ha mature black mangrove (Avicennia germinans) study plot, but were significantly lower during periods of high water levels. Individuals exhibited site fidelity within and between seasons. Feeding areas were small (mean = 0.074 ha ± 0.041 SD) and there was considerable overlap tolerated among conspecifics. Waterthrush density decreased when water submerged their primary foraging substrate: woody debris and pneumatophores. Interannual returns were similar to other Neotropical migrants (mean = 50%) but site persistence was low due to periodic flooding. In September 1998, hurricane Georges flooded the plot and blew down >90% of the black mangrove trees. This drastic habitat alteration was followed by a drastic decline in waterthrushes using the study area. Individuals left feeding areas for overnight roost sites in red mangroves (Rhizophora mangle). This latter finding, coupled with site fidelity and high return rates concurrent with low site persistence, suggests that waterthrushes exhibit high plasticity in their use of habitat during the nonbreeding season, but may rely upon mangroves for overwinter survival.

Quantitative Literacy Across the Curriculum: A Case Study

We describe a quantitative literacy (QL) program at Colby-Sawyer College, a small, residential, liberal arts college in New Hampshire. This program has grown rapidly from a traditional math curriculum to a collegewide understanding of quantitative literacy and voluntary participation by many faculty members in all departments. More than 80% of the faculty agreed that it would be useful for students to be able to use quantitative skills in their courses, but only 24 % thought students were capable of doing very well in mathematics. Twenty-three faculty members attended a summer workshop, funded by NSF, DUE # 0633133, in which they created QL modules for their courses. These participants represented five departments and 13 different disciplines. Modules were created in Biology, Business, Chemistry, Education, English, Environmental Studies, History, Political Science, Psychology, Sociology, and Writing. In addition to assessment of individual modules, a college-wide assessment tool will be administered to first-year students and seniors by participating faculty members. We believe that the rapid growth and success of our program is perhaps due to a combination of characteristics of our institution and our approach. These characteristics include: Involving as many people as possible from many different disciplines from the beginning; a culture of collaboration and innovation at Colby-Sawyer; a supportive administration; the support of NSF that allows concentrated and focused time for faculty with heavy teaching loads; and a faculty focus on the scholarship of teaching.

Quantitative Literacy: Does it Work? Evaluation of Student Outcomes at Colby-Sawyer College

Colby-Sawyer College has adopted a mission for quantitative literacy (QL) to give students the “necessary skills to understand and use quantitative information in their personal and professional lives.” We have implemented an across-the-curriculum approach to develop these skills. As part of this QL program, we administer two assessment tests, one in basic mathematical skills and one that applies those skills, plus an attitude survey to both freshmen and seniors. Three years of data show that seniors score about 10 percentage points higher than freshmen on these tests. However, seniors still scored below 55 percent on both tests, and many cannot answer what we feel are questions that an informed citizen should be able to answer. As evaluation of progress in quantitative skills becomes more common, we suspect that similar results will be found at other colleges. We propose that this deficit in skills results from a lack of practice of the skills students learned before college or a reliance on calculators for simple calculation. If we want to improve the QL preparation of college students, we suggest that there needs to be more widespread evaluation of QL skills at the college level, an increase in QL teaching and learning in the college curriculum, and collaboration with educators at the pre-college level.