Bird Population Density Research Articles

The measurement of granivory by desert rodents, birds and ants: a comparison of an energetics approach and a seed-dish technique

The relative importance of granivorous rodents, birds and ants in four North American arid ecosystems was examined using two methods: an energetics approach (Population Daily Energy Budgets, or PDEBs); and an experimental seed-dish technique. Rodent, bird and ant population densities, combined with species-specific Daily Energy Budgets (DEBs), were used to compute the PDEBs (Kcal/ha/day). The PDEBs were assumed to be an index of the potential seed consumption ‘pressure’ from each taxocene on the seed pool. Seed consumption at sites in the Chihuahuan Desert/Grassland transition zone, the Sonoran and Mojave Deserts, and the Intermountain Basin Shrub-steppe, was estimated by offering each granivore taxocene exclusive access to seed-dishes containing either a native-seed mix or commercial millet. The ratios of rodent, bird and ant PDEBs were compared with the amounts of seeds actually taken by each taxocene from the seed-dishes. The following conclusions were made. (1) Rodents were more ‘important’ (energetically) than birds on the Sonoran, Mojave and Intermountain Basin study sites, but birds were of equal or greater importance as rodents on the Chihuahuan study sites. (2) Birds removed far fewer seeds from seed-dishes than predicted from their PDEBs. (3) Rodents, birds and ants removed more millet and used more seed-dishes containing millet than those containing the native-seed mix. (4) Seed-dish data should be interpreted with caution, due to differential responses by rodents, birds and ants. (5) An energetics approach to desert granivory can provide reliable information about granivore impacts on seed reserves, but requires large data sets and biologically realistic estimators to produce accurate, high-precision results.

Island Land Bird Population Densities in Relation to Island Size and Habitat Quality on the Faroe Islands

Les donnees sur la densite de population des oiseaux de ces iles sont presentees et discutees en relation avec la qualite de l'habitat et le comportement sedentaire ou migrateur des especes. Dans ces iles, quelques especes d'oiseaux terrestres se reproduisent avec des densites inversement proportionnelles a la taille de l'ile. Les relations qualite de l'habitat ― densite sont beaucoup plus complexes

An Analysis of Avifauna‐Resource Relationships on the Serengeti Plains

The objectives of this study were: (1) to test the hypothesis that food was the principal proximate factor limiting the distribution of birds on the Serengeti Plains of Tanzania, and (2) to generate a satisfactory description of the relationships of the Serengeti avifauna to selected habitat factors. I analyzed natural changes in the avifauna among habitats through time and related these changes to variation in avian food and habitat resources. Food limitation was apparently not an important proximate factor affecting short—term variations in bird population densities, although many species were functionally capable of responding to fluctuations in food supply. Habitat partitioning was the principal means of "niche segregation" among the various species. Sites with greatest total avian biomass had low vegetation biomass, low vegetation height, but well—developed vertical vegetation structure. These conditions provided cover along with a great degree of ground—level mobility for most species. Individual bird species were associated with specific types of vegetation structure, while vegetation condition (primarily green biomass) was the main factor associated with increased densities of bird species within vegetation types. Neither conventional competition theory nor Wiens' (1977) "bottle—neck" theory can account for the characteristics of the Serengeti grassland avifauna.

Comparative Use of Four Woodland Habitats by Birds

Bird species diversity (BSD), species richness, population density, and habitat use of individual bird species for riparian woodlands, tree claims, multi-row shelterbelts, and single-row windbreaks were compared to evaluate the impact of changes in woodland availability on bird populations in the northern Great Plains. These indices of bird use were determined by censusing 14 study plots within each habitat type in eastern South Dakota during spring migration, reproduction, and winter seasons. BSD did not differ between riparian woodlands and tree claims or between shelterbelts and windbreaks during any of the seasons studied. However, pooled mean BSD's for riparian woodlands and tree claims were 43 and 39% higher than the pooled mean BSD's for shelterbelts and windbreaks during the spring migration and reproduction seasons, respectively. More species of birds used riparian woodlands than the other habitats during each of the seasons. Tree claims were used most frequently by transient birds. Shelterbelts and windbreaks contribute substantially to the avifauna population of the northern Great Plains, but cannot replace the contribution of riparian habitat in maintenance of BSD.

Bird Population Responses to Converting Chaparral to Grassland and Riparian Habitats

Twenty-one years after chaparral was converted to grassland and riparian habitat in central Arizona, bird population density ranged from a high of 321 pairs per 40 ha in the riparian stringer to a low of 24 pairs per 40 ha on the grassland, compared to 103 pairs per 40 ha in the chaparral. However, the conversion of 40 ha of chaparral resulted in 38 ha of grassland and 2 ha of riparian habitat. Bird density on both areas together was 37 pairs per 40 ha. Thus although popula- tion density, species richness, and diversity were higher in the riparian area when contrasted with the chaparral, there was an overall net difference of 66 fewer pairs per 40 ha in the converted area. Birds and other vertebrates are attracted to riparian habitats throughout the Southwest (Anderson and Ohmart, 1977; Carothers et al., 1974; Stevens et al., 1977; Szaro, 1980). Because of their dense vertebrate populations, increasing importance has been placed on preserving and managing riparian habitat for wildlife (Johnson and Jones, 1977). Unfortunately, the amount and quality of these habitats has been decreasing (Davis, 1977; Ohmart et al., 1977; Engel- Wilson and Ohmart, 1978). A study was initiated in the arid Southwest to determine the effects of chaparral conversion on water yield in central Ariz- ona. After a wildfire, shrub regeneration was suppressed and a watershed con- verted to grass. As a result of this conversion in 1959, a small riparian stand has developed below the stream gauging station at the base of the converted grass area. This study was designed to assess the impact of grass conversion and riparian generation on the breeding birds of Arizona chaparral.

Extinction-Mediated Competition: The Anolis Lizards and Insectivorous Birds of the West Indies

Three lines of evidence suggest that West Indian Anolis lizards and insectivorous birds compete for their arthropod prey: (1) Extensive diet overlaps exist between anoles and insectivorous birds; (2) West Indian anoles are food-limited; (3) there are reciprocal changes in the population densities of anoles and insectivorous birds on islands of different area. On small islands anoles are relatively abundant and on large islands insectivorous birds are relatively abundant. Differences in extinction rates may account for this pattern. West Indian anoles are apparently immune to extinction, but avian extinctions are a regular phenomenon and occur most frequently on small islands. Therefore, if anoles experience ecological release after the extinction of an avian insectivore, anoles should be progressively more abundant on progressively smaller islands. Concomitantly insectivorous birds should be progressively more abundant on progressively larger islands, as is the case.

Nest Sites and Population Demographies of White-Breasted and Pigmy Nuthatches in Colorado

of mountain regions in western North America. In north-central Colorado, these species breed principally in ponderosa pine (Pinus ponderosa) forests of the Transition Zone (Bailey and Niedrach 1965). Despite overall similarity in nesting habitat and breeding schedule, these species differ in nest site preferences and breeding population densities (Stallcup 1968). Both of these nuthatches use (a) natural cavities, (b) cavities bored out by other species, (c) cavities excavated by conspecifics, and (d) modify pre-existing cavities, or (e) excavate their own cavities (Bent 1948, Norris 1958). Very little is known about the historical background of cavities used for nesting; however, Pigmy Nuthatches excavate cavities more frequently than Whitebreasted Nuthatches (Bent 1948). But, even in the case of Pigmy Nuthatches, new cavities are excavated rarely (Norris 1958). Breeding populations of cavity-nesting birds often are limited by the number of suitable and available nest sites (von Haartman 1971, Hogstad 1975). Consequently, population densities of birds within an area, although demonstrating within-year fluctuations due to recruitment, death, and dispersion, exhibit little between-year variation in breeding population densities (Lack 1966). Stallcup (1968) showed that Pigmy Nuthatches have higher breeding densities than White-breasted Nuthatches within a ponderosa pine habitat; however, both species' breeding populations exhibited little annual variation in the number of breeding pairs. I undertook analysis of the nest sites used by these species to see whether nest site availability was a factor associated with the differing levels of breeding populations.

Competition Between Insectivorous Lizards and Birds in Central Panama

The following evidence suggests that birds and lizards compete for their arthropod prey on islands in Lake Gatun, Panama: (1) there is extensive overlap between the diets of a representative bird and lizard, (2) at least one insectivorous lizard, Anolis limifrons , appears to be food-limited, (3) birds appear to have a major impact on arthropod abundances, (4) avian abundance is negatively correlated with the physiological condition and, thus, with the fecundity of female A. limifrons , (5) bird and lizard population densities are negatively correlated. Lake Gatun was formed in 1914. In the intervening years, a great many bird species have been lost from the smaller islands, but very few lizard populations have gone extinct. Ninety-six percent of the between-site variation in avian abundances is accounted for by the number of bird species present at a site. Sites with depauperate avifaunas are characterized by low avian abundances because the species present do not experience ecological release, and resources which are utilized by birds on species-rich sites are not exploited by birds on species-poor sites. Thus, avian abundances are controlled by factors extrinsic to the bird-lizard interaction, and lizards opportunistically increase their abundances at sites with low avian abundances.

Density and Species Richness of Some Forest Bird Communities in South Sweden

Eight forest plots were studied, some of them for five years. Bird community population densities fluctuated from year to year, but the density differences between habitats remained approximately the same. Densities and bird species richness of different forest plots were closely correlated. Both bird community densities and species richness were most successfully predicted from the proportion of the basal tree and shrub area standing dead. Vertical foliage structure and/or number of species of trees and shrubs were minor additional factors. It is suggested that vertical foliage structure is correlated with ecosystem productivity. Food availability is suggested as the ultimate determinant of variations in local bird species richness and community density. The proportion of Turdinae decreased and that of Sylviidae increased with increasing total bird population density. Overall, the bird community structure in different types of forests was similar. The proportion of residents was higher and tropical migrants lower in coniferous than in nearby deciduous forests. Only about 10% of the bird individuals in the coniferous forests were tropical migrants in contrast to about 60% in northeastern North America.

Effects of Fire on Wildlife in a Lodgepole Pine Forest

Effects of a subalpine wildfire on populations of wildlife in north- central Colorado were investigated 8 years after the burn. Inventories of birds and mammals were compared on the 190-ha burn with those from an adjacent similar site of lodgepole pine (Pinus contorta) in 1974. Species diversity for birds and small mammals was greater on the burn than in the adjacent lodgepole. Species composi- tion of both birds and mammals was different in the two habitats, but population densities of birds and small mammals were not significantly different in the two habitats in summer. Mule deer (Odocoileus hemionus) and elk (Cervus canadensis) used the burn more than the lodgepole during winter. Estimated values of total biomass for all birds and mammals were similar for both habitats. In the southern Rocky Mountains, lodgepole at high elevations is an extensive and important forest type which is ecologically adapted to fire and requires fire for establishment (Clements 1910; Mason 1915; Stahelin 1943; Roe et al. 1972). Wildlife relies on vegetation for food and cover and is affected by changes due to fire (Ahlgren and Ahl- gren 1960). Prescribed fires and a let-burn policy for natural fires may be applied with increasing frequency to lodgepole pine forests for management of wildlife habitat. This study examined the effects of fire on wildlife in a lodgepole pine forest at high elevation in Colorado. Population of birds and mammals were studied and described on a burned and on an adjacent unburned subalpine forest; terrestrial poikilotherms were omitted be- cause the one species of toad and one species of snake on the area were uncommon. The study was conducted 8 years after the fire, thereby avoiding initial disruption of the fire and allowing postfire re-estab- lishment of wildlife populations.

Avian Species Diversity in Desert Scrub

Along a gradient of habitat complexity in desert scrub communities of the Sonoran Desert in southern Arizona, nest sites and food niches become more diverse, and breeding bird population density and species diversity increase. Birds are highly specific in their selection of plants for nest placement; densities of nest plants. The MacArthur foliage—height diversity model does not yield consistently accurate predictions of breeding bird species diversities in desert scrub communities. A significant relationship is found between physiognomic coverage diversity and breeding bird species diversity. This index, based on a system of plant life forms, quantifies critical environmental features used by birds in habitat selection. A model that combines aspects of foliage—height diversity and physiognomic coverage diversity may provide greater accuracy and wider applicability for predicting breeding bird species diversity.

Population Structure and Social Organization of Southwestern Riparian Birds

Breeding bird populations were studied on seven riparian woodland study plots in north-central Arizona. The densities of breeding birds varied from 193 to 847 pairs per 40 hectares. These differences were, in part, related to the vegetative structure of the habitat. Bird species diversity (BSD) was not correlated with foliage height diversity (FHD) in riparian habitats consisting of one major vegetational component (the cottonwood tree Populus fremontii ) where these habitats are bordered by agricultural fields. These areas supported the largest breeding bird populations (847, 612, 512, and 425 pairs per 40 hectares) while areas consisting of a mixed deciduous tree and shrub component ( Populus, Platanus, Salix, Acer, Fraxinus, Prosopis, etc. ) had smaller populations of breeding birds (322, 312, and 193 pairs per 40 hectares). On the mixed deciduous woodland areas the correlation between BSD and FHD was similar to what others have found in Eastern deciduous forests. The average weights of individual birds were significantly greater on the homogeneous cottonwood areas ( X ¯ = 46.4 g) than on the mixed deciduous areas ( X ¯ = 22.9 g). Data gathered indicate that two systems of social organization are being maintained. In areas of relatively low population density (mixed deciduous) 57% of the pairs maintained “class A” territories. On areas of relatively high population density (homogeneous cottonwood) only 22% of the pairs exhibited this form of spacing; here, most birds forage freely outside of the riparian habitat. We suggest that the differences in population density and average weights of birds found in the two habitat types are a result of the following: (i) relative productivity of areas adjacent to the riparian habitat, and (ii) degree of intra- and interspecific competition effected by avian populations found breeding in areas adjacent to the riparian habitat.

Methods of Estimating Bird Population Densities during the Winter

Methods of Estimating Bird Population Densities during the Winter

The Effect of Island Area on Population Densities

Bird population densities on the island of Canas, Pearl Archipelago, Panama, were estimated by regression analysis of mist net captures of resident birds. The Canas mist net capture rate is very similar to those from adjacent Puercos, which is one seventh as big but otherwise similar. This not only confirms the main results of the Puercos study but also seems to rule out the action on these birds of the boundary phenomena described for mice by Krebs et al. in which confined populations greatly increased in density because of the small enclosure. The results are consistent with observations made by Diamond on southwest Pacific birds. See full-text article at JSTOR

Density Compensation in Island Faunas

This paper analyzes factors determining the extent of density compensation on islands: i.e., is the summed population density of individuals of all species on islands equal to the summed mainland density as a result of niche expansions and higher abundances of island species compensating for the absence of many mainland species? In addition, a method is described for estimating bird population densities based on analysis of the time dependence or mist—netting yields. Puercos Island in the Pearl Archipelago off Panama has less than one—third as many resident birds species as comparable mainland habitats. Analysis of the Pearl avifauna suggests that about one—quarter of the island species may be relicts of the Pleistocene land bridge and that the remainder are subsequent over—water colonists. The successful colonists are a highly nonrandom sample of the mainland avifauna in such respects as family composition, social structure, and second—growth habitat origin. Song—based censuses and analysis of mist—netting show that Puercos has a slightly density of individuals than the mainland. Niche shifts between islands and mainland, or among different islands, include habitat expansions, wider ranges of vertical foraging strata, abundance increases checkerboard distribution patterns, and decreased morphological variability. Comparison of the present study with other studies shows that summed population densities on islands may be higher than, comparable to, or less than mainland levels, depending upon the particular island, habitat, and group of animals studied. Among factors affecting the extent of density colonists less appropriate to the vacated habitat, tending to lower island densities; and underrepresentation of large species on islands, tending to increase island population densities for a given biomass.

Population Densities of Birds Derived from Transect Counts

GoOD estimates of absolute population density as distinct from indices of relative abundance have been virtually unavailable for nonflocking land birds except in the breeding season when singing males, representing mated pairs, restrict themselves to more or less fixed territories where they or their nests can be counted. The lack of efficient and reasonably accurate census methods applicable at any season has seriously hampered the progress of quantitative studies of avian population ecology. This paper, after reviewing the potentialities and limitations of currently available methods, describes a new method that is, 1) applicable at all seasons, 2) more efficient in terms of area covered per unit of effort than the nest or territory count methods, and 3) comparable in accuracy. The method uses the lateral distribution pattern of all detection points for each species to derive coefficients of detectability with which trail counts may be converted directly to density values in units of birds per 100 acres. The method was developed over a period of 3 years while the author was gathering data on the ecological distribution of birds in mesquite grasslands in southern Texas, pine forests in Florida and the Bahamas, and mixed woodlands in Wisconsin and Michigan.

Seasonal changes of bird cammuuity in the Boso Hills

1. The author, having observed from April of 1967 to May of 1970 the seasonal changes of bird community in Ichihara City, Chiba Prefecture, which is the central part of the Boso Hills, observed birds of 12 orders, 26 families and 48 species.2. In the Boso Hills, compared with other regions, the number of birds and of species of birds are not very large. Two reasons might be given for this. One is that this peninsula consists mainly of low hills with no higher mountains. Atagoyama, which is 405 meters high, for example, is the highest hill-top of this district. Consequently birds are very poorly distributed vertically. The other reason is that the town is far from coastlines and that it has few marshes and it is removed from the stop-over of migrant birds, particularly of water fowls.3. This district is very important as a winter resort of birds, since the weather is very warm here even in winter, unlike the Central Mountain District. 11 species of winter birds were seen.4. The birds in the hills are divided into three types: the farmland type represented by Emberiza cioides, the woodland type represented by Aegithalos caudatus, and the river type represented by Alcedo atthis.5. On further investigation, it will be known that there are many more birds in the Boso Hills. Three years is too short to observe the behavior of birds, especially of winter birds.6. By transect method, the author observed in Tsurumai, Ichihara City, the seasonal changes of the population density of birds in the area of 400m. by 500m., the result of which is classified by species.7. On June 17, 1969 I took a census of birds in Tsurumai, and it was found out that 16 species of bird could be seen between four and six in the morning, 11 species between six and seven in the evening, and five to seven species in the daytime.8. The investigation on the territory of Lanius bucephalus bucephalus and the distribution of Milvus migrans lineatus is reported in this article.

Effect of Cage Size and Bird Density on Performance of Six Commercial Strains of Layers

THE trend toward housing egg-producing strains of chickens at high densities results from rising costs of buildings, equipment and labor. Cages are used more with birds housed at high densities. Logan (1965) reported if birds are to be housed at high densities cages should be used, while floor housing is advantageous for low densities.Effects of cage size, number of birds per cage, and bird density on performance of egg-producing birds have been widely studied (Shupe and Quisenberry, 1961; Lowe and Heywang, 1964; Moore et al., 1965; Cook and Dembnicki, 1966; Elmslie et al., 1966; Wilson et al., 1967; and Champion and Zindel, 1968). In general, egg production declined and mortality increased as bird population or bird density increased.Several researchers found that responses of layer strains differ significantly with various cage-size and bird-density environments (Gowe, 1956; Francis, 1957a; Cook and Dembnicki, 1966; Elmslie et al., 1966; Wilson et al.,…

Effects of Spring Leaf-Fall on Composition and Density of Breeding Birds in Two Southern Arizona Woodlands

Nesting bird composition and population densities reflect the suitability of a given plant community for providing the requisites for survival and reproduction, and also, the selection of these suitable habitats by the birds. Two important features in habitat selection are availability of food and nest-sites (Hilden 1965). Open-nesting species depend on foliage for concealment and protection of the nest from harsh weather and predators (Nice 1957). More than ample foliage for nest-sites is usually available to these species, whereas a major problem confronting hole-nesting species is locating suitable sites (von Haartman 1957). Tree-foliage nesting birds of the oak woodlands in southeastern Arizona may be limited in the same manner as hole-nesters because

Ecologie d’une population de Rapaces diurnes en Lorraine

The seasonal changes in population density of diurnal birds of prey living in a 148 square kilometres area in north-east France have been studied from October 1965 to July 1966. This part of the Lorraine is still rather densely forested and sparsely populated. Thus predators are rather abundant. The eight dominant species are the Buzzard, the Goshawk, the Sparrow hawk, the Red kite, the Rlack kite, the Honey buzzard, the Marsh harrier and the Hobby. Data on population density at various times of the year, on fecundity, and nesting success are given on tables 1 and 2. Habitat preferences, hunting methods, size of home range (table 5) are discussed. Food habits and their seasonal variations have been studied (tables 6 and 7) and an estimation was made of the daily food consumption of the more abundant species. On the whole there was no major «ecological overlap» of the niches of the diurnal birds of prey (table 8) in that part of France. A tentative estimation of the metabolic impact of bird and mammal predators upon the Vertebrate community was made (tables 9, 10, 11, 12). Diurnal birds of prey exert a «predation pressure» which is 10 to 20 times smaller than that of owls and mammalian carnivores taken together. However their selective role must not be underestimated.