Steven C. Latta

Conserving migratory land birds in the New World: Do we know enough?

Migratory bird needs must be met during four phases of the year: breeding season, fall migration, wintering, and spring migration; thus, management may be needed during all four phases. The bulk of research and management has focused on the breeding season, although several issues remain unsettled, including the spatial extent of habitat influences on fitness and the importance of habitat on the breeding grounds used after breeding. Although detailed investigations have shed light on the ecology and population dynamics of a few avian species, knowledge is sketchy for most species. Replication of comprehensive studies is needed for multiple species across a range of areas, Information deficiencies are even greater during the wintering season, when birds require sites that provide security and food resources needed for survival and developing nutrient reserves for spring migration and, possibly, reproduction. Research is needed on many species simply to identify geographic distributions, wintering sites, habitat use, and basic ecology. Studies are complicated, however, by the mobility of birds and by sexual segregation during winter. Stable-isotope methodology has offered an opportunity to identify linkages between breeding and wintering sites, which facilitates understanding the complete annual cycle of birds. The twice-annual migrations are the poorest-understood events in a birds life. Migration has always been a risky undertaking, with such anthropogenic features as tall buildings, towers, and wind generators adding to the risk. Species such as woodland specialists migrating through eastern North America have numerous options for pausing during migration to replenish nutrients, but some species depend on limited stopover locations. Research needs for migration include identifying pathways and timetables of migration, quality and distribution of habitats, threats posed by towers and other tall structures, and any bottlenecks for migration. Issues such as human population growth, acid deposition, climate change, and exotic diseases are global concerns with uncertain consequences to migratory birds and even less-certain remedies. Despite enormous gaps in our understanding of these birds, research, much of it occurring in the past 30 years, has provided sufficient information to make intelligent conservation efforts but needs to expand to handle future challenges.

COMMUNITY RELATIONSHIPS OF AVIAN MALARIA PARASITES IN SOUTHERN MISSOURI

We studied the organization and temporal stability of an assemblage of ma- laria parasites (genera Plasmodium and Haemoproteus) and their passerine avian hosts in a forested study area in southern Missouri, USA, over four years. We detected parasite infections by polymerase chain reaction (PCR) of parasite DNA from host blood samples and identified parasite lineages by sequencing a part of the mitochondrial cytochrome b gene. We obtained 757 blood samples from 42 host species. Prevalence of malaria parasitism judged by PCR averaged 38.6% and varied in parallel in the three most abundant host species over the four years of the study. Parasite prevalence bore a U-shaped relationship to host sample size. Prevalence was weakly positively associated with host body mass, but not with foraging stratum, nest height, nest type, plumage brightness, or sexual dichro- matism. Over the sample as a whole, parasite prevalence did not vary between males and females or between hatch-year and older individuals. We differentiated 34 parasite lineages. The number of host species per lineage varied from one to eight and increased with sample size. We recovered up to 14 lineages of parasite from a single host. Three relatively common lineages in the Ozarks were found nowhere else; four others were recovered from other sites in eastern North America; and six additional well-sampled lineages were distributed in the Greater Antilles among resident island host species. Parasites that are endemic among native species of hosts on the tropical wintering grounds of Ozark birds were recovered from hatch-year birds in the Ozarks, indicating that transmission takes place on the summer breeding grounds, and consequently, that suitable vectors are present in both the temperate and tropical portions of the parasite lineage distributions. We estimate that the number of parasite lineages within a local area will approximate the number of host species and that our perception of host breadth and parasite diversity will increase for most lineages and hosts with increased sampling. Thus, host-parasite relationships in a local area, including the role of parasites in sexual selection and the evolutionary maintenance of sex, are likely to be complex, with population and evolutionary dynamics involving many actors.

DEMOGRAPHIC AND POPULATION RESPONSES OF CAPE MAY WARBLERS WINTERING IN MULTIPLE HABITATS

Wintering Cape May Warblers (Dendroica tigrina) were studied in three habitats along an altitudinal gradient in the Dominican Republic. Results of this study are some of the first to link both population responses and individual condition of nonbreeding birds to prevailing ecological conditions across divergent habitats. Our data suggest that Cape May Warblers are habitat generalists and generally unspecialized resource opportunists, but that differences in food resources result in competitive interactions, sex and age class segregation, and differences in site fidelity and physiological condition among habitats. Diet of the Cape May Warbler varied between habitats: in desert, Cape Mays were primarily insectivores; in dry forest, they foraged primarily on homopteran honeydew; in pine forest, they were principally frugivores. Abundance of warblers as measured by mist-net captures was highest in pine forest sites. Males were more common than females in pine habitat, whereas there was a female-biased sex ratio in other sites. Adult birds were more common in the desert and the pine forest, but there was a bias toward immature birds in dry forest habitat. Overwinter site persistence was 76% in pine, but only 28% and 33% in dry forest and desert, respectively. Annual return rate averaged 57% and did not vary significantly among habitats. Adjusted body mass of site-persistent birds was highest in pine and dry forest and lowest in desert. Pectoral muscle mass scores increased in the pine forest throughout the sampling period, whereas muscle mass scores decreased in the desert. These data suggest that, among the habitats sampled, pine was preferred. It is likely that stability and predictability of resources, particularly fruiting Trema trees and nectar sources, attracted dominant Cape May Warblers to pine forests and kept them as site-persistent individuals in good body condition. In contrast, dry forest may have been suboptimal, unless an individual was able to hold and defend a tree with honeydew-producing homopteran scale insects. Desert thorn scrub was seemingly suboptimal because resources were consistently scarce, and conditions became increasingly difficult during the late-winter dry period.

Landscape effects mediate breeding bird abundance in midwestern forests

We examine the influence of both local habitat and landscape variables on avian species abundance at forested study sites situated within fragmented and contiguous landscapes. The study was conducted over a six year period (1991–1996) at 10 study sites equally divided between the heavily forested Missouri Ozarks and forest fragments in central Missouri. We found greater species richness and diversity in the fragments, but there was a higher percentage of Neotropical migrants in the Ozarks. We found significant differences in the mean number of birds detected between the central Missouri fragments and the unfragmented Ozarks for 15 (63%) of 24 focal species. We used stepwise regression to determine which of 12 local vegetation variables and 4 landscape variables (forest cover, core area, edge density, and mean patch size) accounted for the greatest amount of variation in abundance for 24 bird species. Seven species (29%) were most sensitive to local vegetation variables, while 16 species (67%) responded most strongly to one of four landscape variables. Landscape variables are significant predictors of abundance for many bird species; resource managers should consider multiple measures of landscape sensitivity when making bird population management decisions.

The composition and foraging ecology of mixed-species flocks in pine forests of hispaniola

We determined the flocking propensity of 48 species of birds occurring in native pine forest in the Cordillera Central of the Dominican Republic, and the species composition of 180 mixed-species flocks. Flocks were unusually ubiquitous, with 46 species occurring in at least one flock, 11 species regularly present, and all insectivorous species and all migrant species participating. Most birds encountered were permanent residents, but winter residents (Nearctic migrants) were an important component of the flocks and, as a group, had the highest flocking propensity. Flocks were cohesive and the resident insectivore, the Black-crowned Palm Tanager (Phaenicophilus palmarum) often served as the nuclear species. Censuses suggest species richness within flocks reflects the species present in the habitat, but agonistic interactions indicate that intraspecific aggression may limit the number of individuals of a species in these flocks. Species co-occurrence data indicate that species do not occur independently of one another in flocks. Positive associations were far more common than negative co-occurrences, suggesting mutual habitat dependencies or species interactions within flocks. A non-random association of nearest neighbors also indicated that species may be gaining feeding benefits from flocking by associating as close neighbors with an individual of another species, but we were not able to rule out the possibility that predation is an important selective agent. Intraspecific comparisons of foraging behavior between flocking and solitary birds provides some evidence that individuals modify foraging locations and foraging tactics upon joining mixed-species flocks, and that their foraging behavior tends to converge with the feeding behavior of the nuclear species. An increase in the feeding rate was recorded for one species. These data suggest that at least some species may accrue feeding advantages as flock participants.

Temporal stability of insular avian malarial parasite communities

Avian malaria is caused by a diverse community of genetically differentiated parasites of the genera Plasmodium and Haemoproteus. Rapid seasonal and annual antigenic allele turnover resulting from selection by host immune systems, as observed in some parasite populations infecting humans, may extend analogously to dynamic species compositions within communities of avian malarial parasites. To address this issue, we examined the stability of avian malarial parasite lineages across multiple time–scales within two insular host communities. Parasite communities in Puerto Rico and St Lucia included 20 and 14 genetically distinct parasite lineages, respectively. Lineage composition of the parasite community in Puerto Rico did not vary seasonally or over a 1 year interval. However, over intervals approaching a decade, the avian communities of both islands experienced an apparent loss or gain of one malarial parasite lineage, indicating the potential for relatively frequent lineage turnover. Patterns of temporal variation of parasite lineages in this study suggest periodic colonization and extinction events driven by a combination of host–specific immune responses, competition between lineages and drift. However, the occasional and ecologically dynamic lineage turnover exhibited by insular avian parasite communities is not as rapid as antigenic allele turnover within populations of human malaria.

WINTER SITE FIDELITY OF NEARCTIC MIGRANTS IN SHADE COFFEE PLANTATIONS OF DIFFERENT SIZES IN THE DOMINICAN REPUBLIC

Abstract We studied three Nearctic migrant species (American Redstart [Setophaga ruticilla], AMRE; Black-and-white Warbler [Mniotilta varia], BAWW; Black-throated Blue Warbler [Dendroica caerulescens ], BTBW) wintering in 14 isolated shade coffee plantations (0.1 to 8.7 ha) in the Dominican Republic to determine if site fidelity was comparable to that in tropical forests and if it decreased with plantation size. Site fidelity was measured as the percentage of wandering birds captured in mist nets, as overwinter site persistence of uniquely marked birds observed on the same sites (November to March), and as annual return of marked individuals to previously occupied sites (January to January). The percentages of wanderers in net captures were mostly lower than values reported for natural forests (AMRE 21%, BAWW 12%, BTBW 41%) and did not vary with plantation size. Overwinter site persistence (AMRE 65%, BAWW 65%, BTBW 76%) and annual return (AMRE 34%, BAWW 40%, BTBW 31%) in the plantations fell within the range of values reported for natural forests. Overwinter site persistence decreased with plantation size only in AMRE, although BAWW showed lower persistence in small plantations from early to midwinter. Annual return decreased with plantation size only in AMRE. Despite diminished site fidelity in small plantations, these birds showed some fidelity to small plantations, many of which were smaller than the mean size of winter home ranges.

Species formation by host shifting in avian malaria parasites

Significance Emerging infectious diseases pose threats to humans and livestock, but little is known about the general propensity of parasitic organisms to shift between hosts or the role of host shifting in the diversification of parasite lineages. The malaria parasites of contemporary vertebrate species descended from a common ancestor, likely after the diversification of their major host taxa, requiring rapid speciation and shifting between hosts across large host–taxonomic distances. Examination of sister lineages of avian malaria parasites in the New World suggests that such host shifting is common and often leads to the origin of new evolutionary lineages of parasites. The malaria parasites (Apicomplexa: Haemosporida) of birds are believed to have diversified across the avian host phylogeny well after the origin of most major host lineages. Although many symbionts with direct transmission codiversify with their hosts, mechanisms of species formation in vector-borne parasites, including the role of host shifting, are poorly understood. Here, we examine the hosts of sister lineages in a phylogeny of 181 putative species of malaria parasites of New World terrestrial birds to determine the role of shifts between host taxa in the formation of new parasite species. We find that host shifting, often across host genera and families, is the rule. Sympatric speciation by host shifting would require local reproductive isolation as a prerequisite to divergent selection, but this mechanism is not supported by the generalized host-biting behavior of most vectors of avian malaria parasites. Instead, the geographic distribution of individual parasite lineages in diverse hosts suggests that species formation is predominantly allopatric and involves host expansion followed by local host–pathogen coevolution and secondary sympatry, resulting in local shifting of parasite lineages across hosts.

WINTER SITE FIDELITY OF PRAIRIE WARBLERS IN THE DOMINICAN REPUBLIC

Abstract Wintering Prairie Warblers (Dendroica discolor) were studied in pine forest, desert thorn scrub, and desert wash habitats of the Sierra de Bahoruco, Dominican Republic from October–April 1996–1998 and January–February 1999. We used mist netting, color banding, and extensive resighting of color-banded birds to quantify habitat-specific demographies, site fidelity, and fitness indices. Males predominated early in the season in pine habitat while females predominated in the desert. Sex ratios were more equal through the drier months of late winter although females continued to be more frequent in the desert. Adult birds predominated throughout all habitats and time periods. Nonterritorial wanderers were far more common in desert habitats than in pine forest, and females predominated among these wanderers. Site persistence was moderately high, but variable between habitats and time periods, and was significantly lower in the drier months in thorn scrub than it was in the desert wash or pine forest. Annual return rates were generally high and did not vary significantly among years. Birds showed significant declines in pectoral-muscle-mass scores in both of the desert habitats but not in the pine forest. Data presented here emphasize the importance of dry-season events and habitat heterogeneity in the winter ecology of migratory birds. Fidelidad al Territorio Invernal de Dendroica discolor en la República Dominicana Resumen. En los meses de octubre a abril de 1996 a 1998 y enero y febrero de 1999, investigamos a Dendroica discolor en el bosque de pino, en los matorrales del desierto y en el arroyo seco de desierto en la Sierra de Bahoruco, República Dominicana. Para llevar a cabo esto, se utilizaron redes ornitológicas y anillos colorados. Se realizó una revisión extensiva de las aves anilladas para cuantificar la demografía en los tres hábitats, la fidelidad al territorio invernal, y los índices de aptitud (“fitness”). Al comenzar el invierno, los machos predominaron en el bosque de pino mientras que las hembras lo hicieron en el desierto. La proporción entre los machos y las hembras mantuvo una mayor igualidad entre los sexos en los meses más secos del invierno, aunque hay que considerar que las hembras predominaban en el desierto. Se observó que las aves adultas predominaban en los tres hábitats durante todo el período investigado. Las aves sin territorio eran más comunes en el desierto y eran mayormente hembras. La fidelidad al lugar fue moderadamente alta pero variable entre los hábitats y los períodos y fue significativamente más baja en los meses secos en los matorrales del desierto que en los arroyos secos y los bosques de pino. La tasa anual de retorno de esta especie fue generalmente alta y no varió significativamente entre años. La masa de los músculos pectorales bajó significativamente en las aves que se encontraban en los matorrales del desierto y en el arroyo seco pero no en los bosques de pino. Los datos mencionados aquí acentúan la importancia de eventos que ocurren en la época seca del período invernal y de la heterogenidad del hábitat en la ecología invernal de las aves migratorias.

WINTER BIRD COMMUNITIES IN FOUR HABITATS ALONG AN ELEVATIONAL GRADIENT ON HISPANIOLA

Abstract We used five years of mist-net-capture and point-count data to quantify avian diversity in four habitats along a 1750-m elevational gradient in the Dominican Republic. These habitats include desert thorn scrub, dry forest, pine forest, and montane broadleaf forest, which together comprise more than two-thirds of existing forest on Hispaniola. In midwinter samples we recorded 74 species of landbirds, including 22 species of latitudinal migrants and 19 endemics. The highest diversity and species richness were found in pine forest and dry forest, but the highest capture rate of individuals was in desert thorn scrub. Abundance of migrant individuals was highest in pine forest, whereas pine and montane broadleaf forest contained the highest proportion of endemic species and individuals, and more habitat specialists. Among mist-net captures, insectivorous species and individuals predominated in all habitats except in dry forest, where more omnivorous individuals were captured. A more complex pattern was found in point-count detections: insectivorous species and individuals predominated in most habitats; omnivorous species and individuals were most frequently counted in montane broadleaf and dry forest, respectively; and nectarivorous individuals were most common in desert thorn scrub. Data presented here represent the most complete quantitative record of avian abundance and distribution on Hispaniola. This study not only details the value of these four habitats to various suites of species, but also emphasizes the importance of montane broadleaf and pine forests to large numbers of Neotropical migrants and Hispaniolan endemics, some of which are narrowly restricted to these habitats. Comunidad de Aves de Invierno en Cuatro Hábitats a lo largo de una Gradiente Altitudinal en la Isla Española Resumen. Utilizamos cinco años de datos de captura con redes ornitológicas y de conteos en puntos para cuantificar la diversidad de aves en cuatro hábitats a lo largo de un gradiente altitudinal de 1750 m en la República Dominicana. Estos hábitats incluyen matorral espinoso seco, bosque seco, bosque de coníferas y bosque latifoliado montano, los que en conjunto ocupan más de dos tercios del área boscosa del país. En enero y febrero, registramos 74 especies de aves terrestres, incluyendo 22 especies migratorias latitudinales y 19 endémicas. La mayor diversidad y riqueza de especies fue encontrada en el bosque de coníferas y en el bosque seco, pero la mayor tasa de captura de individuos se presentó en el matorral espinoso seco. La abundancia de individuos migratorios fue mayor en el bosque de coníferas, mientras que los bosques de coníferas y latifoliado montano presentaron la mayor proporción de individuos y especies endémicas y el mayor número de especialistas de hábitat. Entre las capturadas, las especies e individuos insectívoros predominaron en todos los hábitats, excepto en el bosque seco dónde se capturaron más individuos omnívoros. Entre las aves registradas en los puntos de conteo, los insectívoros también predominaron en la mayoría de los hábitats, pero registramos más especies omnívoras e individuos omnívoros en el bosque latifoliado nublado y bosque seco respectivamente. Los individuos nectarívoros fueron más comunes en el matorral espinoso seco. Los datos presentados aquí representan la cuantificación más completa de la abundancia y distribución de aves en Española. Esta investigación no sólo describe en detalle el valor de estos hábitats para los distintos grupos de especies, sino que también enfatiza la gran importancia de los bosques latifoliado montano y de coníferas para un gran número de aves migratorias Neotropicales y endémicas de Española, algunas de las cuales se encuentran estrechamente restringidas a estos hábitats.