Joseph J. Nocera

Inadvertent social information in breeding site selection of natal dispersing birds

Several species use the number of young produced as public information (PI) to assess breeding site quality. PI is inaccessible for synchronously breeding birds because nests are empty by the time the young can collect this information. We investigate if location cues are the next best source of inadvertent social information (ISI) used by young prospectors during breeding site choice. We experimentally deployed ISI as decoys and song playbacks of breeding males in suitable and sub-optimal habitats during pre- and post-breeding periods, and monitored territory establishment during the subsequent breeding season for a social, bobolink (Dolichonyx oryzivorus), and a more solitary species, Nelsons sharp-tailed sparrow (Ammodramus nelsoni). The sparrows did not respond to treatments, but bobolinks responded strongly to post-breeding location cues, irrespective of habitat quality. The following year, 17/20 sub-optimal plots to which bobolink males were recruited were defended for at least two weeks, indicating that song heard the previous year could exert a ‘carry-over attraction’ effect on conspecifics the following year. Sixteen recruited males were natal dispersers, as expected when animals have little opportunity to directly sample their natal habitat quality. We suggest that differences in breeding synchronicity may induce an equivalent clinal distribution of ISI use.

Point count summary statistics differentially predict reproductive activity in bird-habitat relationship studies

Point count summary statistics (e.g. mean abundance, maximum abundance, frequency and presence/absence) reflect different assumptions about behavioral and population processes. In this paper we (1) determine the frequency and usage trends of different point count summary statistics in recent ornithological literature, and (2) assess how well point count data, summarized using five common statistics, predict an alternate measure of habitat quality–reproductive activity. For the 100 journal years we reviewed (10 journals over 10xa0years), 148 papers used point counts to evaluate bird habitat relationships. The number of papers using point counts has increased over the decade. Mean abundance, the most common summary statistic, was used more than twice as frequently as the next most common summary statistics. Only 25.7% (38 papers) provided a justification for use of a particular summary technique. We conducted point counts in three Canadian study regions (New Brunswick, Nova Scotia, and Newfoundland and Labrador) comprised of two ecosystem types (forest and grassland). While there was a statistically significant positive correlation between point count data and reproductive activity data for most species, we found that point counts were often unsuccessful at predicting reproductive activity in forest birds. For species where point counts adequately predicted reproductive activity mean abundance and frequency were consistently the best predictors. Our results indicate that statistics using information on intra-season (multiple-visit) occupancy tend to be better estimators of reproductive activity.

Habitat Relationships of Three Grassland Breeding Bird Species: Broadscale Comparisons and Hayfield Management Implications

Generalized recommendations for the conservation of birds in agro-ecosystems have been elusive because studies are often of a local nature, and do not compare source data against those from other regions. In this study, we developed geographically broad habitat relationship models to provide conservation prescriptions for three species that breed in farmed grasslands: Bobolink (Dolichonyx oryzivorus), Savannah Sparrow (Passerculus sandwichensis), and Nelson’s Sharp-tailed Sparrow (Ammodramus nelsoni subvirgatus). We develop models from our study in Nova Scotia, Canada and confront them with independent data from Wisconsin, USA pastures and Iowa, USA restored prairies. Vegetation that was higher and denser in the prebreeding season was linked to increased occupancy rates and abundance of Bobolinks in each study region. Providing tall spring grass is easily accomplished by not cutting late in the previous year. Savannah Sparrows were instead associated with shorter and sparser spring grass, which highlights the need to simultaneously provide heterogeneous habitat for otherwise ecologically similar species. Nelson’s Sharp-tailed Sparrows were more likely to occur, and be numerous, in areas with greater availability of drainage ditches. They and several other species would benefit from provision of ditches with adequate vegetation to promote occupancy. By combining these with other well-established recommendations, such as a delayed first harvest, a greater net conservation benefit can be realized from these working landscapes. RESUME. Les recommandations d’ordre general pour la conservation des oiseaux des ecosystemes agricoles sont difficiles a definir parce que les etudes n’ont souvent qu’une portee locale et ne comparent pas les donnees d’origine a celles d’autres regions. Dans cette etude, nous avons developpe des modeles de relations avec l’habitat a grande echelle dans le but de fournir des recommandations pour la conservation de trois especes qui nichent dans les prairies cultivees : le Goglu des pres (Dolichonyx oryzivorus), le Bruant des pres (Passerculus sandwichensis) et le Bruant de Nelson (Ammodramus nelsoni subvirgatus). Nous avons elabore des modeles a partir de notre etude en NouvelleEcosse, au Canada, et nous les avons compares a des donnees independantes recoltees aux Etats-Unis, dans des pâturages au Wisconsin et des prairies restaurees en Iowa. La vegetation plus haute et plus dense avant la saison de nidification etait associee a des taux d’occupation plus eleves et a un plus grand nombre de goglus dans chaque aire d’etude. Il est facile d’obtenir de l’herbe haute au printemps en evitant de couper tardivement l’automne precedent. A l’oppose, les Bruants des pres etaient associes a la presence d’herbes courtes et eparses au printemps, ce qui met en evidence la necessite de fournir des habitats heterogenes pour des especes neanmoins ecologiquement similaires. Les Bruants de Nelson frequentaient davantage et etaient plus nombreux dans les aires ou il y avait plus de fosses de drainage. Cette espece et plusieurs autres profiteraient de la presence de fosses bordes de vegetation adequate. On peut obtenir un benefice net de conservation plus important dans ces paysages anthropiques en combinant ces recommandations a d’autres deja reconnues, comme celle de retarder la premiere recolte.

Managing for Habitat Heterogeneity in Grassland Agro-Ecosystems Influences the Abundance of Masked Shrews (Sorex cinereus)

ABSTRACT Many agri-environment programs prescribe modified farming practices and provision of heterogeneous habitat types, such as fallow field edges and shelterbelts. The conservation benefit of these actions to biodiversity has been well described. However, the response of insectivorous small mammals to habitat heterogeneity in agro-ecosystems has received little empirical attention. We compared the abundance of the masked shrew (Sorex cinereus) between hayfields and adjacent mesic old-fields in Nova Scotia, Canada. Masked shrews were almost twice as abundant in old-field habitat and were linked closely to abundance of Aranea (spiders), Coleoptera (beetles), and Malacostraca (slugs). This implies that mesic old-field habitat is beneficial to masked shrews and is a likely population source for shrews that occur in hayfields. Because masked shrews consume large quantities of invertebrate prey (that are often considered agricultural pests), we suggest that old-fields are an important habitat to include in agro-ecosystems that should benefit both wildlife and agricultural producers.

Stable Isotopes from Museum Specimens May Provide Evidence of Long-Term Change in the Trophic Ecology of a Migratory Aerial Insectivore

Identifying the mechanisms of ecological change is challenging in the absence of long-term data, but stable isotope ratios of museum specimen tissues may provide a record of diet and habitat change through time. Aerial insectivores are experiencing the steepest population declines of any avian guild in North America and one hypothesis for these population declines is a reduction in the availability of prey. If reduced prey availability is due to an overall reduction in insect abundance, we might also expect populations of higher trophic level insects to have declined most quickly due to their greater sensitivity to a variety of disturbance types. Because nitrogen isotope ratios (delta 15N) tend to increase with trophic-level, while delta 13C generally increases with agricultural intensification, we used delta 15N and 13C values of bird tissues grown in winter (claw) and during breeding (feathers) from museum specimens spanning 1880–2005, and contemporary samples from breeding birds (2011–2013) to test for diet change in a migratory nocturnal aerial insectivore, Eastern Whip-poor-will (Antrostomus vociferus) breeding in Ontario, Canada. To test if environmental baselines have changed as a result of synthetic N fertilizer use, habitat conversion or climate, we also sampled delta 15N values of three potential prey species collected from across the same geographic region and time period. Over the past 100 years, we found a significant decline in delta 15N in tissues grown on both the breeding and wintering grounds. Prey species did not show a corresponding temporal trend in delta 15N values, but our power to detect such a trend was limited due to higher sample variance. Amongst contemporary bird samples, delta 15N values did not vary with sex or breeding site, but nestlings had lower values than adults. These results are consistent with the hypothesis that aerial insectivore populations are declining due to changes in abundance of higher trophic-level prey, but we caution that museum-based stable isotope studies of terrestrial food chains will require new approaches to assessing baseline change. Once addressed, an ability to decode the historical record locked inside museum collections could enhance our understanding of ecological change and inform conservation decisions.

Nightjars may adjust breeding phenology to compensate for mismatches between moths and moonlight

Abstract Phenology match–mismatch usually refers to the extent of an organisms ability to match reproduction with peaks in food availability, but when mismatch occurs, it may indicate a response to another selective pressure. We assess the value of matching reproductive timing to multiple selective pressures for a migratory lunarphilic aerial insectivore bird, the whip‐poor‐will (Antrostomus vociferus). We hypothesize that a whip‐poor‐wills response to shifts in local phenology may be constrained by long annual migrations and a foraging mode that is dependent on both benign weather and the availability of moonlight. To test this, we monitored daily nest survival and overall reproductive success relative to food availability and moon phase in the northern part of whip‐poor‐wills breeding range. We found that moth abundance, and potentially temperature and moonlight, may all have a positive influence on daily chick survival rates and that the lowest chick survival rates for the period between hatching and fledging occurred when hatch was mismatched with both moths and moonlight. However, rather than breeding too late for peak moth abundance, the average first brood hatch date actually preceded the peak moth abundance and occurred during a period with slightly higher available moonlight than the period of peak food abundance. As a result, a low individual survival rate was partially compensated for by initiating more nesting attempts. This suggests that nightjars were able to adjust their breeding phenology in such a way that the costs of mismatch with food supply were at least partially balanced by a longer breeding season.

The Relevance of Local-Scale Relationships to Habitat Management and Landscape Patterns

In his response to our article (Nocera et al. 2007), Thogmartin (2007) invokes a quotation from Wiens et al. (1987) that implies our study was somehow invalid because we did not sample at multiple spatial scales. This needs to be put into context, as the subsequent paragraph in Wiens et al.’s paper supports our justification by stating “an analysis... that seeks a consistent relation to habitat features over the entire range will fail to demonstrate any but the strongest patterns.” It was indeed the strongest patterns that we sought to identify, and we feel this renders our models conservative and therefore more reliable.