Garden bird feeding predicts the structure of urban avian assemblages

Households across the developed world cumulatively spend many millions of dollars annually on feeding garden birds. While beneficial effects on avian assemblages are frequently claimed, the relationships between levels of garden bird feeding and local avian populations are unknown. Using data from a large UK city, we show that both avian species richness and abundance vary across different socioeconomic neighbourhood types. We examined whether patterns in bird feeding could explain this variation. The density of bird feeding stations across the urban environment was strongly positively related to avian abundance, after controlling for differences in habitat availability. This effect was almost exclusively driven by the abundance of those species known to utilize garden feeding stations frequently. In contrast, the density of feeding stations had no effect on avian species richness. We also examined variation in the proportion of households in different communities that provide food for birds, a factor that is not correlated with feeder density. The prevalence of bird feeding across different neighbourhoods declined as socioeconomic deprivation increased, and increased with avian species richness and abundance. Our results suggest that the provision of supplementary food for birds by multiple landowners across a city can impact the status of urban bird populations. The potential for harnessing these actions for conservation needs to be explored.     

Fire regime shifts affect bird species distributions

Aim Fire is a major driver of ecosystem structure and process, and shifts in fire regimes are implicated in the decline of many species. Shifting fire regimes have been documented around the world, and fire frequency and extent is predicted to increase in many areas because of changes in both climate and land management. Here, we evaluate how predicted increases in fire frequency are likely to impact on species distributions. Location The tropical savannas of northern Australia. Methods We developed distribution models for 44 bird species using the modelling algorithm Maxent. Our models incorporated bird locality records and environmental variables including climate, total fire frequency and the subset of fire frequency occurring late in the dry season. We investigated the effect of increasing total fire frequency and increasing fire late in the dry season, on species distributions by projecting species model algorithms onto scenarios of incrementally increased total fire frequency. Results The probability of presence for most species was higher when fire frequency late in the dry season was low. Species showed a mixed response to an overall increase in total fire frequency, with one‐third predicted to increase in distribution. However, almost all species (98%) showed a decrease in predicted range with increased late‐dry season fire, and species distribution area was generally negatively correlated with an increase in late‐dry season fire. Main conclusions Our study highlighted the array of responses of species to increasing fire frequency and suggested that increased fire frequency late in the dry season is detrimental to most savanna‐restricted bird species. The understanding of individual species’ preferences for particular fire frequencies is important for informed conservation planning.     

Vegetation structure influences foraging decisions in a declining grassland bird: the importance of fine-scale habitat and grazing regime

Capsule: Whinchat Saxicola rubetra foraging behaviour was significantly influenced by habitat structure and grazing.

Aims: To assess how foraging habitats selected by breeding Whinchats differed from wider territory attributes under contrasting grazing management in multiple upland areas in Scotland: principally sheep grazed, Red Deer grazed or ungrazed, and to identify how differing land use may limit suitable foraging areas.

Methods: We compared fine-scale vegetation structure in patches chosen for foraging by Whinchats in contrasting grazing management regimes.

Results: Whinchats were less likely to forage in patches with a greater cover of bracken and tall non-bracken vegetation, regardless of grazing regime. Grass cover influenced foraging behaviour in ungrazed habitats only, where Whinchats were less likely to forage in areas with high grass cover.

Conclusion: Whinchats appear to require a mosaic or range of sward structures within breeding territories, highlighting the importance of establishing how vegetation structure influences breeding birds at different spatial scales. Our results suggest that suitable foraging patches were plentiful within grazed habitats but potentially limited in ungrazed habitats. Further work is needed to identify management regimes and interventions to maintain conditions suitable for breeding Whinchats that are compatible with other land use and conservation objectives.     

Tryptophan feeding adversely influences pregnancy

Additional tryptophan during pregnancy reduces embryo and neonate survival in the golden hamster, $\text{Mesocricetus auratus}$.Relatively small doses of exogenous serotonin have been reported to cause abortions in several vertebrate species (1, 2, 3, 4, 5). Smaller doses reduce litter sizes, increase still births and neonate abnormalities, and otherwise influence pregnancy adversely. These effects are produced by serotonin throughout pregnancy, beginning at implantation (6).The availability of tryptophan is probably the most important rate limiting factor in serotonin synthesis (7). Inasmuch as tryptophan is an essential amino acid and is not synthesized by the body, the diet is the sole source; studies have shown that increases (8) or decreases (9) in dietary tryptophan lead to concomitant changes in serotonin content. Because tryptophan is employed in humans to promote sleep (10, 11, 12) and to decrease appetite (13) we felt it might be important to test whether increased amounts of diet tryptophan can adversely influence pregnancy.     

Dominant climate influences on North American bird distributions

Aim Geographic distributions of species are constrained by several factors acting at different scales, with climate assumed to be a major determinant at broad extents. Recent studies, however, have challenged this statement and indicated that climate may not dominate among the factors governing geographic distributions of species. Here, we argue that these results are misleading due to the lack of consideration of the geographic area that has been accessible to the species. Location North America. Methods We generated null distributions for 75 North American endemic and 19 non‐endemic bird species. For each species, climatic envelopes of observed and null distributions were modelled using neural networks and generalized linear models, and seven climatic predictors. Values of the area under the receiver–operating characteristic curve (AUC) based on models of observed distributions were compared with corresponding AUC values for the null distributions. Results More than 82% of the endemic species showed AUC higher for the observed than for the null distributions, while 63% of the non‐endemic species showed such a pattern. Main conclusions We demonstrate a dominant climatic signal in shaping North American bird distributions. Our results attest to the importance of climate in determining species distributions and support the use of climate‐envelope models for estimating potential distributional areas at the appropriate spatial scales.     

Competition and introduction regime shape exotic bird communities in Hawaii

Complex combinations of historical and local-regional processes determine the assembly of ecological communities. We investigated such processes in the Hawaiian introduced avifauna, comprising 140 years of historical records of invasions and extinctions of birds. Here the particular introduction regime (i.e., colonization attempts and number of introduced species) and priority effects constitute the historical (and regional) component, and competition is the local component. These processes are theoretically supported by means of a Lotka–Volterra model of species competition, finding that changes in the specific introduction regime might result in different extinction dynamics. Both field data and model outcomes support the biotic resistance hypothesis, so that the invasibility of new incomers decrease with species richness. Finally, we found that the resistance to new invaders depends on the particular introduction regime. Thus, community assembly models built to predict the success of exotic species should consider more scenarios than random introduction regimes.     

Living in the city: resource availability, predation, and bird population dynamics in urban areas

This article explores factors that shape population structure in novel environments that have received scant theoretical attention: cities. Urban bird populations exhibit higher densities and lower diversity. Some work suggests this may result from lower predation pressure and more predictable and abundant resources. These factors may lead to populations with few winners and many losers regarding access to food, body condition, and reproductive success. We explore these hypotheses with an individual-energy-based competition model with two phenotypes of differing foraging ability. We show that low frequency resource fluctuations favor strong competitors and vice versa. We show that low predation skews equilibrium populations in favor of weak competitors and vice versa. Increasing the time between resource pulses can thus shift population structure from weak to strong competitor dominance. Given recent evidence for more constant resource input and lower predation in urban areas, the model helps understand observed urban bird population structure.     

Incubation temperature influences survival in a small passerine bird

In birds parental incubation behaviour is an important factor shaping the environmental conditions under which the embryos develop, and sub‐optimal incubation temperatures are known to negatively affect early growth and development. It is less well known if variation in incubation temperature can impose life‐long differences in individual performance and survival. In the present study we investigated the effects of incubation temperature on long‐term survival in a small passerine bird. Using our captive population of the zebra finch Taeniopygia guttata we artificially incubated eggs at three biologically relevant temperatures (35.9, 37.0 and 37.9°C) for two‐thirds of the incubation period and then monitored individual lifespan of the hatched chicks for two and a half years. We found that individuals from eggs incubated under the lowest temperature exhibited significantly lower long‐term survival compared to those which had been incubated at the highest temperature. Our results show that incubation temperature in birds, and thus parental incubation behaviour, play an important role in shaping the life‐history trajectories of offspring.     

Experimental evidence for real-time song frequency shift in response to urban noise in a passerine bird

Research has shown that bird songs are modified in different ways to deal with urban noise and promote signal transmission through noisy environments. Urban noise is composed of low frequencies, thus the observation that songs have a higher minimum frequency in noisy places suggests this is a way of avoiding noise masking. Most studies are correlative and there is as yet little experimental evidence that this is a short-term mechanism owing to individual plasticity. Here we experimentally test if house finches (Carpodacus mexicanus) can modulate the minimum frequency of their songs in response to different noise levels. We exposed singing males to three continuous treatments: low–high–low noise levels. We found a significant increase in minimum frequency from low to high and a decrement from high to low treatments. We also found that this was mostly achieved by modifying the frequency of the same low-frequency syllable types used in the different treatments. When different low-frequency syllables were used, those sung during the noisy condition were longer than the ones sang during the quiet condition. We conclude that house finches modify their songs in several ways in response to urban noise, thus providing evidence of a short-term acoustic adaptation.     

Determinants of bird populations in an urban area

The effects of suburb age and distance from remnant native vegetation on the species richness and density of bird populations in Canberra were studied from June 1982 to May 1983. Mean total number of bird species increased with age of the suburbs < 12 years old. The density of birds also increased with suburb age. The number of open forest and woodland species increased with the age of the suburbs but the number of grassland and exotic species remained largely unchanged. These increases in bird species richness and density represented a response to changes in habitat conditions over time and were not a direct response to the suburb age per se. Such habitat changes reflected the growth of trees and, to a lesser extent, the increased cover of shrubs. The numbers of open forest, woodland and grassland species decreased with distance of suburban sites from native vegetation areas. The number of exotic species, however, remained unaffected. The density of individual birds of grassland and exotic species increased with distance of sites from remnant native vegetation.     

Foraging on human-derived foods by urban bird species

Capsule: Providing peanuts on bird feeders was shown to attract more individuals and more species than providing cheese or bread.

Aims: To investigate how the provision of different human-derived foods affected visit rates of urban birds at bird feeders.

Methods: A fully replicated study design was set up in parkland, offering a binary choice from three food types (peanuts, bread and cheese) on bird tables. Birds were observed by using a scan-sample method.

Results: Peanuts attracted more visits, and a greater diversity of bird species, than cheese or bread. This preference was strongest for Blue Tits Cyanistes caeruleus and Great Tits Parus major, whereas European Robins Erithacus rubecula visited all food types equally, and Blackbirds Turdus merula preferred cheese. Bread was the most consumed food type when measured by mass, but this could be linked to varying bite sizes.

Conclusion: Our results indicate that birds preferred to visit feeding stations with the most protein- and energy-rich foods, but that some birds still chose the carbohydrate-rich bread. The findings indicate that peanuts, rather than household scraps like bread and cheese, attract the highest number of species and individuals to bird tables. The findings will be of interest to the public and to organizations providing information on bird feeding for recreational purposes.     

Foraging ecology of a tropical aerial feeding bird guild

The feeding ecology of the constituent members of the aerial feeding bird guild was studied in Malaya. Although numbers changed with the movements of migrants, more birds were seen feeding over forested habitats than open areas. Methods of ecological isolation were seen in morphology, flight behaviour and food selection. Seasonal changes in foraging behaviour associated with breeding and migration were found in Pacific Swallows and Barn Swallows. Migrant species were observed to mix freely with residents and no evidence was found for competitive exclusion between the two groups.     

Environmental influences on the orientation of free-flying nocturnal bird migrants

Autumn nocturnal bird migration was investigated using radar and visual observations. Multivariate analyses assessed the influence of environmental variables on orientation. Two categories of birds were distinguished: (1) shorebirds and waterfowl migrating in flocks; and (2) passerine birds flying singly. These two classes of migrants employ different orientation mechanisms. Landbirds selectively flew with the wind, regardless of its direction or speed or whether the skies were clear or overcast. Shorebirds and waterfowl flew in directions independent of wind in light or moderate winds. The accuracy of passerine orientation was not correlated with any of the variables examined. The passerine orientation observed cannot be accounted for by stellar orientation, but is explicable via orientation on the basis of wind direction.