Hummingbird Populations Research Articles

ANNUAL SURVIVAL AND RECRUITMENT IN A RUBY-THROATED HUMMINGBIRD POPULATION, EXCLUDING THE EFFECT OF TRANSIENT INDIVIDUALS

We estimated annual apparent survival, recruitment, and rate of population growth of breeding Ruby-throated Hummingbirds (Archilochus colubris), while controlling for transients, by using 18 years of capture-mark-recapture data collected during 1984–2001 at Hilton Pond Center for Piedmont Natural History near York, South Carolina. Resident males had lower apparent survival (0.30 ± 0.05 SE) than females (0.43 ± 0.04). Estimates of apparent survival did not differ by age. Point estimates suggested that newly banded males were less likely than females to be residents, but standard errors of these estimates overlapped (males: 0.60 ± 0.14 SE; females: 0.67 ± 0.09). Estimated female recruitment was 0.60 ± 0.06 SE, meaning that 60% of adult females present in any given year had entered the population during the previous year. Our estimate for rate of change indicated the population of female hummingbirds was stable during the study period (1.04 ± 0.04 SE). We suggest an annual goal of ≥64 adult females and ≥64 immature females released per banding area to enable rigorous future tests for effects of covariates on population dynamics. Development of a broader cooperating network of hummingbird banders in eastern North America could allow tests for regional or metapopulation dynamics in this species. Sobrevivencia Anual y Reclutamiento en una Población del Picaflor Archilochus colubris Excluyendo el Efecto de Individuos Ocasionales Resumen. Estimamos la sobrevivencia anual aparente, reclutamiento y tasa de crecimiento en una población reproductiva del picaflor Archilochus colubris, controlando por la presencia de individuos ocasionales. Utilizamos datos de 18 años de captura-marcaje-recaptura colectados entre 1984 y 2001 en Hilton Pond Center for Piedmont Natural History en cercanías de York, Carolina del Sur. Los machos residentes presentaron una sobrevivencia aparente menor (0.30 ± 0.05 EE) que las hembras (0.43 ± 0.04). Las estimaciones de la sobreviviencia aparente no difirieron entre edades. Estimaciones puntuales sugirieron que los machos marcados por primera vez tuvieron una menor probabilidad de ser residentes que las hembras, pero los errores estándar de estas estimaciones se sobrepusieron (machos: 0.60 ± 0.14 EE; hembras: 0.67 ± 0.09 EE). Para las hembras el reclutamiento estimado fue 0.60 ± 0.06 EE, lo que significa que el 60% de las hembras adultas presentes en un año determinado entraron a la población durante el año anterior. Nuestra estimación de la tasa de cambio indicó que la población de picaflores hembra fue estable durante el período de estudio (1.04 ± 0.02 EE). Para permitir futuras pruebas rigurosas sobre las covariables asociadas a las dinámicas poblacionales, sugerimos una meta anual de ≥64 hembras adultas y ≥64 hembras inmaduras liberadas por área de anillado. La creación de una amplia red cooperativa de anilladores de picaflores en el este de Norteamérica podría permitir estudiar y entender mejor las dinámicas regionales o metapoblacionales de esta especie.

The Effect of Floral Abundance on Feeder Censuses of Hummingbird Populations

Numbers of Broad-tailed Hummingbirds (Selasphorous platycercus) captured each summer from 1979-1989 at the Rocky Mountain Biological Laboratory were quite variable, ranging from 115 (1981) to 348 (1989), with new birds usually outnumbering returning (previously banded) birds. Capture numbers were negatively correlated with the abundance of four species of flowers they visited, Erythronium grandiflorum, Delphinium nelsonii, Ipomopsis aggregata and Delphinium barbeyi; flower numbers were also highly variable during the study period. Since most of the captures were at feeders, these data suggest that in years with high floral abundance feeders are less attractive, while in years with low floral abundance hummingbirds with nests or territories at greater distances increase their use of the feeders. This interpretation is supported by seasonal variation in use of feeders, which is highest during the beginning and end of the season when floral abundance is lowest. Estimates of hummingbird density based on activity at feeders may thus be affected by the availability of floral food resources.

Effects of indiscriminate foraging by tropical hummingbirds on pollination and plant reproductive success: experiments with two tropical treelets (Rubiaceae).

In cloud forest at Monteverde, Costa Rica, two common treelets (Palicourea lasiorrachis and Cephaelis elata, both Rubiaceae) depend simultaneously on one hummingbird population (Lampornis calolaema) for pollination. Both species are distylous and self-incompatible. In laboratory experiments, we examined possible effects of indiscriminate foraging by hummingbirds among flowers of both species, as observed in the field, on pollination of Palicourea. In each of 35 trials, captive L. calolaema probed 2 flowers from pin plants of Palicourea followed by 20 thrum flowers of the same species, with either 0, 2, or 10 Cephaelis flowers intervening. We assessed pollen transfer by staining and counting pin pollen tubes growing in thrum styles; counts of 0, 1, or ≥2 pollen tubes relate directly to seed output (0, 1, or 2 seeds per fruit, respectively). Intervening Cephaelis flowers sharply reduced pollen receipt by thrum flowers of Palicourea and reduced some aspects of pollen dispersal from pins as well, thereby curtailing maternal and paternal reproductive potential of Palicourea. Such effects of interspecific pollen loss on reproductive output may lead to strong competition among some, though not all, combinations of plant species pollinated by L. calolaema or of other plant combinations that share animal pollinators.

Nectar‐Feeding Birds on Trinidad and Tobago: Comparison of Diverse and Depauperate Guilds

Nectar‐Feeding Birds on Trinidad and Tobago: Comparison of Diverse and Depauperate Guilds

The comparative biology of longevity and lifetime energetics

The relationships between longevity and cumulative energy metabolism in homeothermic vertebrates are explored interspecifically as allometric functions, and intraspecifically in terms of metabolic extension, through restriction of energy intake, hibernation, and torpor. A new equation for marsupial longevity is presented. The first evidence of age-dependent mortality in a population of hummingbirds is shown. Hummingbirds are seen to be model subjects for the study of longevity in nature.

Site-fidelity, longevity, and population dynamics of broad-tailed hummingbirds: a ten year study.

In the course of other studies we have amassed a decade of records from banding, and observing the nests of, a breeding population of broad-tailed hummingbirds in Colorado, USA. In addition we have less extensive banding records for two other hummingbird species that migrate through the area but do not breed there. The rate of return of broad-tails between consecutive breeding seasons has been as high as 70% for females and 27% for males, suggesting substantial site fidelity and malebiased dispersal or mortality; our records also suggest that rufous hummingbirds are faithful to a particular migratory route. The oldest recaptured birds were at least eight years old, an age that exceeds predictions based on allometric extrapolation from other bird species; the apparent yearly survival rate of females is also unexpectedly high for birds of such small body mass. The earliest broad-tails to arrive at the start of the breeding season appear to be older, experienced individuals. Reuse of a specific nest site between consecutive years by the same female or different females seems to depend on the success of nesting efforts at that site. We have calculated the rate of change in size of the broad-tail population based on our estimates of female survivorship and fledging success. By this method the population appears to be declining, although nest counts themselves suggest that numbers of breeding females have remained fairly constant at least over the last seven years of our study.

Sobre la ecología reproductiva de Nicotiana glauca Grah: una maleza de distribución cosmopolita

Se estudiaron algunos eventos reproductivos de Nicotiana glauca Grah., una maleza de distribución cosmopolita, en el Pedregal de San Angel (SO de la Cuenca del Valle de México). La especie es esencialmentne ornitófila, pues es visitada por colibríes (fam. Trochilidae ) en el con tinente americano, mientras que en Africa y Australia la visitan otras aves pertenecientes a las familias Nectariniidae y Meliphagidae respectivamente. Dada su conducta de floración prolongada, su gran producción de néctar y las características de éste, los colibríes dependen de las poblaciones de N. glauca , sobre todo en los periodos de escasez de alimento, lo cual, al mismo tiempo, es benéfico para la reproducción de la planta. Más aún, tal parece que N . glauca , en tanto que especie introducida recientemente en México, ha tenido un papel importante en la ecología de los visitantes, sobre todo en lo que se refiere a sus movimientos estacionales. Las cuatro especies de colibríes identificadas en el estudio tienen dos estilos de forrajeo (estilo nómada y estilo territorial ), los cuales tienen implicaciones en el flujo de polen entre los individuos de N. glauca . Bajo este marco, se discute el posible papel que tiene los visitantes ilegítimos (robadores de néctar). Las técnicas experimentales utilizadas para conocer el sistema de reproducción demostraron que N . glauca es auto-compatible y capaz de auto-polinizarse, los cuales son elementos importantes en su éxito como especie colonizadora. Finalmente, se describen los tres diferentes mecanismos de dispersión de las semillas y se discute su importancia a la luz actual patrón de distribución de la especie.

Energy limitation of hummingbird populations in tropical and temperate communities.

Regular censuses were conducted at both a temperate alpine and a tropical lowland site to determine seasonal changes in the composition of hummingbird communities and the availability of their food. From these data we calculated the total daily energy demand by the hummingbirds (Daily Energy Expenditure; DEE) and the daily energy supply available from floral nectar (Daily Energy Production; DEP) for each community census. Despite differences in habitat type and hummingbird community structure between these two sites, the hummingbird populations were often at or near carrying capacity. On average, all of the daily nectar production was cropped by the birds. We suggest that the supply/demand economics of coevolved mutualisms favour the evolution of complete resource use.

Capricious mountain weather: a driving variable in hummingbird territorial dynamics

A violent summer hailstorm destroyed a large proportion of flowers in one of several meadows in a small mountain basin. This decimation of the resource base resulted in a dramatic decrease in the number of fall migrant rufous hummingbirds holding territories there, supporting the hypothesis that hummingbird populations closely track their food supplies. We found no evidence that the individuals displaced by the hailstorm established territories in neighboring meadows, and we therefore concluded that these individuals were forced into suboptimal habitats nearby or emigrated from the basin.

El ciclo anual en una comunidad coadaptada de colibríes y flores en el bosque tropical muy húmedo de Costa Rica

A community of 22 species of hummingbirds and over 45 species of omithophilous plants was studied over a seven-year period in the humid Caribbean lowlands of Costa Rica. There are two approximately equal peaks of blooming of hummingbird flowers in the year, during the dry season (March) and early in the rainy season (July-August); with a severe scarcity of flowers between November and January, at the end of the rainy season. The epiphytes of the forest canopy flower mainly in the dry season, understory plants mostly in the wet season, and at light gaps, edges, and in old second growth flowers are present year-round. Habitat shifts of hummingbirds are closely associated with flowering of preferred food plants, as is the differential habitat use by the sexes of some species. Migration of some species into and out of La Selva also reflects the cycle of flower abundance.In general, the breeding seasons of the hummingbirds coincide with the first peak, and molting seasons With the second peak of flowering. Deviations from this pattern are few, and generally reflect the dependence of a given hummingbird upon a given flower species, or physiological mechanisms permitting molt-breeding overlap. The maximum body weight and fat reserves also occur during the second flowering peak, and both decline rapidly during the following season of flower scarcity. The low point in body weight occurs during this lean season, while the annual low of fat reserves comes in the following breeding season; another body component, probably muscle protein, must therefore be used as well as fat by the birds to survive the season of flower scarcity, when most of the annual mortality probably occurs.Year-to-year variations in rainfall are considerable, but the hummingbirds are normally buffered from these by a series of compensatory phenological reactions among the plants that tend to maintain a regular, staggered sequence of flowering peaks. Nevertheless, a severe moisture stress, such as the drought of early 1973, may disrupt these patterns and have drastic effects on hummingbird populations.

Discrimination of colors by the black-chinned hummingbird,Archilochus alexandri

The color vision of a population of black-chinned hummingbirds was studied by behavioral methods. Birds were attracted to feeders equipped with tungsten lamps and interference filters. Results are based on counts of approximately 5700 visits by 92 ± 5 birds. Population size was estimated by mistnetting and marking 29 hummingbirds, 22 of which could be recognized individually during the course of the experiments.

Ecologic Overlap and Interspecific Strife in Breeding Population of Anna and Allen Hummingbirds

Analyses of interspecific competition in natural populations are fundamental to modern theory in ecology and evolution. Yet, at least among higher vertebrates, few examples with supporting details are on record, and current theories require corroboration in the field (Errington 1946; Crombie 1947; Richards 1948; Lack 1949). This will come slowly, chiefly because the proper recording and interpretation of competitive incidents in the field require a long and intimate field acquaintance with a given species and because the details of such incidents are often elusive or subtle. Also, the true nature of adaptive differences between closely similar species may escape detection unless these are observed in competition (Lack 1944; Crombie 1947). The object of this paper is to examine ecological differences between two sympatric species of hummingbirds which overlap in both geographic and habitat distribution, providing an example of what, in Schmalhausen's (1949) classification of competitive situations, is termed active intergroup competition. The Anna hummingbird (Calypte anna) and the Allen hummingbird (Selasphorus sasin, formerly S. alleni) are almost restrictedly Californian in breeding distribution, and their breeding ranges overlap along the coast from the San Francisco Bay region to Ventura County (Grinnell and Miller 1944). The evidence to be presented here was obtained in the course of a five-year census, in the period from 1943 to 1947, of the breeding population of hummingbirds in Woolsey Canyon, which drains into Strawberry Creek on the west side of the Berkeley Hills. The study area, now a part of the University of California campus, totals about 125 acres and, until 1948, supported a complex of woodland and chaparral vegetation surrounded by open grassy slopes such as typically fills the canyons in the central Coast Ranges (see Fig. 1). Studies of territoriality in hummingbirds reported earlier (Pitelka 1942) have been continued, and while data presented in this paper concern specifically the populations of Woolsey Canyon, much original information on behavior to be reported elsewhere has been used in interpreting the data on these populations.