Riparian Bird Research Articles

A SEVEN-YEAR COMPARISON OF RELATIVE-ABUNDANCE AND DISTANCE-SAMPLING METHODS

Abstract We used data from statewide surveys of riparian birds in Utah, 1992–1998, to compare relative-abundance and distance-sampling methods. By generating relative-abundance indices with point-count methods and density with point-transect sampling methods, we examined whether the assumptions underlying each method were met during field surveys for four bird species (Brown-headed Cowbird [Molothrus ater], Bullock's Oriole [Icterus bullockii], Warbling Vireo [Vireo gilvus], and Yellow Warbler [Dendroica petechia]). Point-count methods failed to reasonably meet the fundamental assumption of constant proportionality, with estimated detectability varying 3- to 5-fold despite the use of widely accepted and well-standardized methods. Population trends based on relative abundance were subsequently unstable, often varying in both magnitude and direction with the survey plot radius used (25 m, 50 m, or unlimited distance). Distance-sampling methods appeared to meet critical assumptions, were robust to assumption...

The American mink: The triumph and tragedy of adaptation out of context

The American mink has spread widely beyond its native North America due to the activities of fur traders. The mink is an extremely adaptable, generalist predator. Over two continents, the American mink is associated with problems in the conservation of local species because of their impact on both prey and competitors. Here, we review the impact of American mink on native species, stemming from over a decade of research, and concentrate on two examples: the impact of American mink on the water vole in Britain and on the European mink in Eastern Europe. While the near extinction of the water vole in Britain and that of the European mink in Eastern Europe are largely due to predation and interspecific aggression, respectively, both may have been affected by a multitude of factors acting synergistically. Terns, and other seabirds, are impacted by mink predation; the effect on riparian bird species is less clear but may potentially be high. Emerging principles, supported by preliminary evidence, suggest that the return of the larger otter in the United Kingdom may be detrimental to mink populations. The impact of, or on, the current recovery of the polecat in the United Kingdom is unknown but evidence from Eastern Europe suggests that American mink negatively affect at least female polecats. We conclude by briefly presenting two case studies of small‐scale mink removal and discuss considerations for future control projects. To mitigate mink impact on a larger scale we suggest a holistic approach, involving mink removal, habitat restoration, and recovery of native competitors.

Rivers, dams, and willow flycatchers: a summary of their science and policy connections

The southwestern willow flycatcher (Empidonax traillii extimus) is a riparian bird that spends winter months in Central and South America and summer breeding months in riparian zones of the American Southwest. Decline of the willow flycatcher population to less than 1000 breeding pairs prompted the Federal government to declare the species endangered, triggering a major recovery effort. The most important aspect of recovery is management and improvement of the riparian habitat of the bird population. Although the direct management of the species is primarily a biological issue, fluvial hydrology and geomorphology play an important role in understanding the dynamics of the present bird population and in designing a recovery plan because these physical systems are the substrates for the living communities which include the birds. Contributions of geomorphology and hydrology to the recovery plan include the use of watersheds and river basins as planning and evaluation units; understanding the connections between fluvial forms and riparian vegetation; implications for the bird population of the magnitude, frequency, duration, timing, and rate of change for various river discharges. The installation and operation of dams are the most important causes of hydro-geomorphic and ecological change in the region, so that management of these structures offers primary opportunities to improve the physical and biological conditions for the endangered species.

The Orange River avifauna: abundance, richness and comparisons

Like many other southern African rivers, the avifaunal richness and abundance of the Orange River, southern Africa's longest, remains virtually unknown. Given that the Orange River runs through hyper-arid regions in its lower reaches, its linear oasis effect and its role as a reservoir for Red Data bird species is likely but has not been quantified. Two surveys either side of the border town of Noordoewer, in the rainy and dry seasons of 1996 and 1997 deter-mined that species richness was higher in riverine habitat (71 species) than in the surrounding Nama Karoo (46 species) confirming the linear oasis effect. Surveys revealed five Namibian Red Data species. Peregrine Falcons, Falco peregrinus, and African Fish Eagles, Haliaeetus vocifer, were relatively common while the endangered Cape Eagle Owl, Bubo capensis, occurred sporadically. Among wetland Red Data bird species, Black Storks, Ciconia nigra, occurred in less disturbed areas, and White-backed Night Herons, Gorsachius leuconotus, were an unexpected species at this locality. The overall species richness of 103 birds and a density of riparian birds of 31 -3 4 birds/10 km, makes the lower Orange River avifauna similar to the Cunene River but tenfold less abundant than Namibia's other perennial rivers. Despite the low diversity, the arid habitats of the lower Orange River support greater diversity than more easterly regions when all current surveys of richness and abundance from Lesotho to the mouth on the Namib coast are combined. This east-west trend may be explained by the slower flow and warmer water of the lower Orange River but natural turbidity and regulation may explain the generally low diversity and abundance indices. Major rivers in southern Africa appear to have been over-looked as wetland habitats, and further avifaunal surveys of all of them are recommended.

Landscape indicators of human impacts to riverine systems

Detecting human impacts on riverine systems is challenging because of the diverse biological, chemical, hydrological and geophysical components that must be assessed. We briefly review the chemical, biotic, hydrologic and physical habitat assessment approaches commonly used in riverine systems. We then discuss how landscape indicators can be used to assess the status of rivers by quantifying land cover changes in the surrounding catchment, and contrast landscape-level indicators with the more traditionally used approaches. Landscape metrics that describe the amount and arrangement of human-altered land in a catchment provide a direct way to measure human impacts and can be correlated with many traditionally used riverine indicators, such as water chemistry and biotic variables. The spatial pattern of riparian habitats may also be an especially powerful landscape indicator because the variation in length, width, and gaps of riparian buffers influences their effectiveness as nutrient sinks. The width of riparian buffers is also related to the diversity of riparian bird species. Landscape indicators incorporating historical land use may also hold promise for predicting and assessing the status of riverine systems. Importantly, the relationship between an aquatic system attribute and a landscape indicator may be non-linear and thus exhibit threshold responses. This has become especially apparent from landscape indicators quantifying the percent impervious surface (or urban areas) in a watershed, a landscape indicator of hydrologic and geomorphic change.

Riparian bird communities in relation to land management practices in floodplain woodlands of south-eastern Australia

Bird communities are declining in south-eastern Australia and riparian woodlands are critical habitats for birds in this agricultural region. We investigated how terrestrial bird communities varied with different land management practices (levels of grazing by domestic livestock and extent of clearing) and with habitat quality on the floodplains of the Murrumbidgee and Murray Rivers. Bird community composition in ungrazed and lightly grazed sites was significantly different to that in more heavily grazed sites, and these differences were related to tree and shrub cover, as well as tree species diversity and abundance of standing dead trees. Grazing appeared to have an effect on bird communities separate from that caused by clearing. Indicator species were identified for the effects of grazing and clearing. Grazing by livestock has had negative impacts on riparian birds through degradation of habitat quality. A combination of lower stocking rates, strategic placement of off-river watering points for stock, and the introduction of rotational grazing practices may be used to restore riparian habitat quality. The grazing-sensitive species we identified could be used as indicator species for the success of rehabilitation efforts.

Nesting Habitat and Reproductive Success of Southwestern Riparian Birds

AbstractVegetation structure and floristic composition strongly influence the structure of bird communities. To assess the influence of vegetation and other environmental characteristics on songbirds, we quantified nest-site characteristics and reproductive success of a riparian songbird community in Arizona. Although we found interspecific variation in characteristics associated with nest sites, we identified two suites of species that chose sites with similar characteristics. These “nest groups” were explained largely by nest height and characteristics of nest trees. Overall, nest success was low for songbirds in this community, and averaged 23%. The most common cause of nest failure was predation (81%), although brood parasitism by Brown-headed Cowbirds (Molothrus ater) was highest at nests of Bell's Vireos (Vireo bellii) (29%). No vegetation or environmental features were associated with the likelihood of cowbird parasitism for any species; nest success for Bell's Vireos was negatively associated with the amount of netleaf hackberry (Celtis reticulata) in the understory. Arizona sycamore (Platanus wrightii) and netleaf hackberry trees contained 41% and 17% of all nests, respectively, and therefore provide critically important nesting substrates for birds in this rare yet diverse vegetation community.

Nesting Habitat and Reproductive Success of Southwestern Riparian Birds

Nesting Habitat and Reproductive Success of Southwestern Riparian Birds

Bird distribution in riparian vegetation in the extensive natural landscape of Australia’s tropical savanna: a broad‐scale survey and analysis of a distributional data base

AbstractAim(a) To characterize the riparian bird assemblage, and its variation, in a large area of northern Australia; (b) to examine the distinctiveness of this assemblage in relation to the broader landscape; (c) to consider the influence of disturbance on this assemblage; (d) to examine temporal variability in the riparian assemblage, and especially evidence for seasonal movements between riparian and non‐riparian areas.Location c. 620,000 km2 of the seasonal tropics of the Northern Territory, Australia.Methods(a) Synchronous sampling of birds in riparian and adjacent non‐riparian areas at 100 sites stratified across 13 catchments and an extensive rainfall gradient. (b) Repeat visits to 13 of these sites at contrasting seasons. (c) Analysis of a larger distributional database to assess the relative occurrence of records in riparian areas relative to non‐riparian areas.ResultsSpecies richness and the total abundance of birds was significantly greater in riparian zones than in matched non‐riparian areas, especially where the riparian zones contained extensive cover of rain forest plants and Melaleuca. Similarity in bird species composition between riparian zones and adjacent non‐riparian areas was generally low, and this distinction was greatest in lower reaches of the rivers and where the riparian zone contained no eucalypts. Bird species composition varied gradationally from riparian zones in high rainfall areas, through riparian zones in low rainfall areas and non‐riparian zones in high rainfall areas, to non‐riparian zones in low rainfall areas. Many species occurred widely across the riparian sites sampled. Of ninety‐four species recorded from more than five sites, forty‐five species were significantly more abundant in riparian zones than in matched non‐riparian zones, whereas this pattern was reversed for only twelve species. There was little association between foraging group and preference for riparian zones. Species had highly idiosyncratic distributions across the riparian samples, with the most common trend being an association with mean annual rainfall. Many species were significantly more closely associated with riparian zones in lower rainfall areas than in higher rainfall areas. Indeed, many species typical of higher rainfall areas extended into lower rainfall areas only, or mainly, along riparian strips. There was some temporal fluidity in bird species composition of riparian zones, suggesting seasonal movements between riparian zones and the surrounding landscape. There was little evidence that disturbance was a major factor influencing the distribution of riparian birds, probably because other major geographical and environmental gradients probably dwarfed the influence of the relatively minor variation between samples in disturbance.Main conclusionsThe bird fauna of riparian areas is distinct from that of the surrounding savannas, and especially so in lower rainfall areas. Riparian vegetation allows many species to extend their distributions into lower rainfall areas. The riparian assemblage is loosely structured, in that most species have idiosyncratic distributions. As at least some bird species move seasonally between riparian and non‐riparian areas, conservation management must ensure that these connections are maintained.

Concordance of taxonomic composition patterns across multiple lake assemblages: effects of scale, body size, and land use

We assessed environmental gradients and the extent to which they induced concordant patterns of taxonomic composition among benthic macroinvertebrate, riparian bird, sedimentary diatom, fish, and pelagic zooplankton assemblages in 186 northeastern U.S.A. lakes. Human population density showed a close correspondence to this region's dominant environmental gradient. This reflected the constraints imposed by climate and geomorphology on land use and, in turn, the effects of land use on the environment (e.g., increasing lake productivity). For the region as a whole, concordance was highest among assemblages whose taxa were relatively similar in body size. The larger-bodied assemblages (benthos, birds, fish) were correlated most strongly with factors of broader scale (climate, forest composition) than the diatoms and zooplankton (pH, lake depth). Assemblage concordance showed little or no relationship to body size when upland and lowland subregions were examined separately. This was presumably because differences in the scales at which each assemblage integrated the environment were obscured more locally. The larger-bodied assemblages showed stronger associations with land use than the diatoms and zooplankton. This occurred, in part, because they responded more strongly to broad-scale, nonanthropogenic factors that also affected land use. We argue, however, that the larger-bodied assemblages have also been more severely affected by human activities.

Bird communities and extended biotic index (EBI) in some tributaries of the Tiber river

1. Riparian birds and macroinvertebrates were studied in five reaches of four tributaries of the Tiber river (Italy). The first aim was to check if stream quality, assessed by extended biotic index (EBI) values, could represent change in the riparian zone, assessed through the bird community. The second was to consider whether stream quality affects the presence of riverine bird species. 2. Stream quality and richness of the riparian bird community were related. In streams with more disturbed macroinvertebrate communities, but also in agricultural areas, the relative frequency of granivorous species increased in the riparian zone. 3. Dippers Cinclus cinclus occurred exclusively in reaches with the best stream quality, but the relationship between grey wagtails Motacilla cinerea and stream quality was less clear. 4. These results support the judicious use of riverine and riparian birds as biological indicators. Copyright © 1999 John Wiley & Sons, Ltd.

Concordance of taxonomic richness patterns across multiple assemblages in lakes of the northeastern United States

We investigated the concordance of taxonomic richness patterns and their environmental correlates for assemblages of benthic macroinvertebrates, riparian birds, sedimentary diatoms, fish, planktonic crustaceans, and planktonic rotifers in 186 northeastern U.S. lakes. Taxon counts were standardized with respect to sampling effort using rarefaction. The degree of concordance among assemblage richness measures was low, but this was at least partly attributable to measurement precision. Aspects of lake morphology (area, depth) superseded other environmental features (climate, human development, water chemistry, nearshore physical habitat) as correlates of assemblage richness and were the strongest source of concordance. The benthic macroinvertebrates, birds, fish, and zooplankton all showed positive associations between richness and lake area. The diatoms showed negligible associations between richness and area and negative associations between richness and depth. Associations with human development were much weaker than with lake morphology and varied from positive (fish, planktonic crustaceans) to negative (diatoms). We conclude that taxonomic richness alone may be of ambiguous value as an indicator of biological integrity in lakes and that its natural drivers must be controlled for prior to assessing anthropogenic effects.

Predicting the impacts of urbanization on riparian bird communities

In 1995, birds were surveyed in riparian woodlands along a gradient of urbanization in the Santa Clara Valley, CA, USA, in order to determine the relationships between riparian bird communities and urbanization. Bird species richness and density decreased at a location as the number of bridges near that location increased and as the volume of native vegetation decreased. Species richness also increased as the distance to the nearest building and the width of the riparian habitat increased. Canonical correspondence analysis confirmed that bird community structure was influenced strongly by these variables. Many individual species responded significantly to variables associated with urbanization, most having lower densities on more urbanized sites. Whereas previous studies have demonstrated substantial effects of urbanization on bird communities in the habitats being directly altered, this study indicates that urbanization on lands adjacent to intact riparian woodlands has substantial impacts on riparian bird communities.

Concordance of taxonomic composition patterns across multiple lake assemblages: effects of scale, body size, and land use

We assessed environmental gradients and the extent to which they induced concordant patterns of taxonomic composition among benthic macroinvertebrate, riparian bird, sedimentary diatom, fish, and pelagic zooplankton assemblages in 186 northeastern U.S.A. lakes. Human population density showed a close correspondence to this region's dominant environmental gradient. This reflected the constraints imposed by climate and geomorphology on land use and, in turn, the effects of land use on the environment (e.g., increasing lake productivity). For the region as a whole, concordance was highest among assemblages whose taxa were relatively similar in body size. The larger-bodied assemblages (benthos, birds, fish) were correlated most strongly with factors of broader scale (climate, forest composition) than the diatoms and zooplankton (pH, lake depth). Assemblage concordance showed little or no relationship to body size when upland and lowland subregions were examined separately. This was presumably because differences in the scales at which each assemblage integrated the environment were obscured more locally. The larger-bodied assemblages showed stronger associations with land use than the diatoms and zooplankton. This occurred, in part, because they responded more strongly to broad-scale, nonanthropogenic factors that also affected land use. We argue, however, that the larger-bodied assemblages have also been more severely affected by human activities.

Concordance of taxonomic richness patterns across multiple assemblages in lakes of the northeastern United States

We investigated the concordance of taxonomic richness patterns and their environmental correlates for assemblages of benthic macroinvertebrates, riparian birds, sedimentary diatoms, fish, planktonic crustaceans, and planktonic rotifers in 186 northeastern U.S. lakes. Taxon counts were standardized with respect to sampling effort using rarefaction. The degree of concordance among assemblage richness measures was low, but this was at least partly attributable to measurement precision. Aspects of lake morphology (area, depth) superseded other environmental features (climate, human development, water chemistry, nearshore physical habitat) as correlates of assemblage richness and were the strongest source of concordance. The benthic macroinvertebrates, birds, fish, and zooplankton all showed positive associations between richness and lake area. The diatoms showed negligible associations between richness and area and negative associations between richness and depth. Associations with human development were much weaker than with lake morphology and varied from positive (fish, planktonic crustaceans) to negative (diatoms). We conclude that taxonomic richness alone may be of ambiguous value as an indicator of biological integrity in lakes and that its natural drivers must be controlled for prior to assessing anthropogenic effects. Resume : Nous avons etudie la concordance de profils de diversite taxonomique avec leurs correlats environnementaux chez des groupements de macroinvertebres benthiques, d'oiseaux de rivage, de diatomees sedimentaires, de poissons et de crustaces et de rotiferes planctoniques dans 186 lacs du nord-est des Etats-Unis. Nous avons normalise les

Riparian bird densities along four tributaries of the Río Paraná in north-east Argentina

This article does not have an abstract.

Seasonal use by birds of stream‐side riparian habitat in coniferous forest of northcentral British Columbia

To determine use of riparian habitats by birds in the northern coniferous forest of British Columbia, we censused birds and vegetation along 500 m transects placed parallel and perpendicular to three second‐order streams. Censuses were conducted during spring, summer, autumn, and winter to investigate how use of riparian habitat changed seasonally. Stream‐side riparian zones were characterized by a dense understorey of deciduous vegetation not found in the upslope forest. Nine bird species preferred the riparian understorey for breeding, six preferred it only during migration. Neotropical migrants (16 of 46 species) were more closely associated with stream‐sides than year‐round residents (11 species). Some breeding birds (five species) were significantly negatively associated with riparian habitats. The density of riparian birds declined with distance upstream but did not decline up to 250 m away from the stream. The more extensive riparian areas downstream supported a greater density of birds in all seasons compared to upstream areas, but more species only in spring and autumn. Species that nested in non‐riparian areas in summer used riparian habitat in autumn, making riparian corridors in the northern coniferous forest important during migration. Maintaining both riparian and upslope habitats is necessary to preserve species diversity al the landscape level.

The effect of pulp and paper mill effluent on an insectivorous bird, the tree swallow

Pulp mill effluent is known to affect freshwater biota in various ways. However, its effects on riparian birds that feed on insects emerging from aquatic ecosystems have not been examined. This study examined diet, circulating sex steroids, highly carboxylated porphyrins (HCPs), activity of the mixed function oxygenase enzyme 7-ethoxyresorufin-O-deethylase (EROD), the liver somatic index and reproductive performance and nestling size in tree swallows, an insectivorous bird, at sites located upstream and downstream from two pulp mills in western Canada during 1993–1996. The tree swallow diet consisted of 50–60% insects of aquatic origin. In general, physiological biomarkers in tree swallows located downstream from the pulp mill effluents did not differ from those at upstream sites, suggesting that dietary exposures to pulp mill effluents at these sites were insufficient to elicit responses. Nevertheless, it is noteworthy that 17β-oestradiol was lower in incubating females at a site downstream from one of the pulp mills in 1 of 2 years. In addition, HCPs in tree swallows downstream from the other pulp mill were elevated significantly. Reproductive performance by tree swallows did not differ significantly between upstream and downstream locations at either mill although there was a definite trend towards enhanced reproduction at downstream sites. At both pulp mills, 16 day old nestlings were significantly larger at downstream sites compared to their counterparts at upstream sites in at least 1 year. The improved reproduction and larger nestlings at downstream sites may be the result of a greater food supply, consistent with the nutrient enrichment effect often seen below pulp mills.

Avian Nest Success in Relation to Past Grazing Regimes in a Montane Riparian System

One possible link between livestock grazing and bird population declines is variation in nest predation rates. To explore this possibility we documented vegetational differences in a montane riparian community subdivided by a fence, one side of which traditionally has been summer-grazed, and the other side rested from grazing for 30 years. We found that ground vegetation was more abundant, willows (Salix spp.) less abundant, and vertical vegetational diversity was lower on the grazed relative to the rested side. Predation rates on real nests were higher on the grazed side compared to the rested side. Artificial nests were placed (I) in mixed conifer vegetation to mimic the most common nest types currently present in the riparian zone, (2) in streamside willows that differed in abundance across the fence, and (3) in old-willow remnants distant from the stream, which were equally abundant on both sides of the fence. All artificial above-ground nests, and ground nests in the old-willow experiment, suffered greater predation rates on the grazed compared to the rested side. Thus, livestock grazing may not only affect availability of nesting substrates for riparian birds by reducing streamside vegetation, but could influence bird populations by facilitating nest predation, possibly by increasing detectability of nests or through changes in predator assemblage.

Declines in Abundance and Species Richness of Birds Following a Major Flood on the Upper Mississippi River

-We examined the abundance and species richness of birds breeding in floodplain forests of the Upper Mississippi River from 1992 to 1994 to identify effects of a major flood in 1993 on the bird assemblage. Sixty-five study plots were divided into treatments and controls based on whether they were flooded in 1993. Among 84 species observed on all plots, 41 species decreased in abundance from 1992 to 1994, 13 species increased, and numbers of 5 species were unchanged. Sample sizes were inadequate to evaluate trends for 25 species. Species richness declined over the three-year period. The main effect was significant in 20 of the 36 species tested. Cool, wet conditions may have contributed to poor reproductive success in 1993 and resulted in widespread declines in abundance during the year following the flood. Bird abundance increased on most unflooded plots in 1993, probably because birds were displaced from flooded plots. This pattern was most striking for Neotropical migrants, species preferring habitat edges, lower-canopy nesters, and species that forage in the air. We suggest that periodic major flooding maintains suitable floodplain habitat for Prothonotary Warblers (Protonotaria citrea) in the face of competition with House Wrens (Troglodytes aedon) for nest sites. Received 30 November 1995, accepted 22 January 1996. FLOODPLAINS ARE DYNAMIC HABITATS where periodic flooding creates natural disturbances that set back succession and provide new sites for plant establishment (Peck and Smart 1986, Kupfer and Malanson 1993, Jones et al. 1994, Sparks 1995, Yin and Nelson 1995). Large floodplain forests like those of the Upper Mississippi River are uncommon in northern landscapes (Mitsch and Gosselink 1993) and provide unique habitats that support a high abundance and diversity of birds (Grettenberger 1991, Best et al. 1995, Knutson et al. 1996). Few studies have examined the avifauna of large floodplain forests (Emlen et al. 1986, Decamps et al. 1987, Knutson 1995), and studies of the effects of floods that include pre-flood data are even less common (Knopf and Sedgwick 1987). Direct effects of flooding on birds nesting in floodplains tend to be minor because spring floods usually recede by midto late May. Summer floods are rare and usually of short duration. However, major floods of long duration or high amplitude can create large-scale disturbances that dramatically change vegetative I Present address: U.S. Geological Survey, Biological Resources Division, Upper Mississippi Science Center, 2630 Fanta Reed Road, La Crosse, Wisconsin 54602, USA. E-mail: melinda_knutson@nb?.gov cover (Yin et al. 1994). Bird assemblages may respond to changes in availability of rnest sites and food resources caused by these disturbances. Flooding had a major effect or a riparian bird community in Arizona by elirminating cottonwood and willow nesting habitat (Hunter et al. 1987). Depending upon the severity of the disturbance, some species may in(rease in abundance while others decline. In addition, flooding may maintain suitable habitat for some bird species that are uncommon in drier, less-disturbed habitats. Rainfall during May to August 1993 in the Upper Mississippi River basin reached historically high levels (ca. twice normal), zpproximating 75to 300-year recurrence i ztervals (Wahl et al. 1993, Interagency Floodplain Management Review Committee 1994). River water levels were well above normal throughout the breeding season (Parrett et al. 1993). We examined the effects of this major flood on the abundance and species richness of bird,; breeding in floodplain forests by comparing cLata collected from 1992 to 1994. We conside-ed our data in relation to two hypotheses of how the flood and associated weather patterns aLffected the floodplain bird assemblage. The Flood Disturbance Hypothesis proposes that the pattern of change in abundance will differ between flooded and unflooded plots because structural