Foraging guild perturbations and ecological homogenization driven by a despotic native bird species

Anthropogenic activities often cause specialized and fragmentation‐sensitive species to be replaced by competitive commensal or invasive species, resulting in reduced diversity and biotic homogenization. However, biotic homogenization driven by increased dominance of a native species has rarely been investigated. Increased abundance of competitive species can have important consequences for assemblage dynamics including homogenization of foraging strategies and, potentially, ecological services. This study assesses how changes to bird assemblages due to the occurrence of an aggressive honeyeater alter the foraging profiles of avifauna in 400 woodland sites in nine study regions across eastern Australia, and explores the potential implications for ecological services. We compared beta diversity among sites with a high and low abundance of the aggressive Noisy Miner Manorina melanocephala. Shifts in ecological characteristics of bird assemblages of sites with high and low abundance of Noisy Miners, including mean and variation in niche position, bill length and body size, were explored. Sites with a high abundance of Noisy Miners were more taxonomically and ecologically homogeneous and had fewer species than sites with a low abundance of Noisy Miners. The mean niche positions of bird assemblages changed and were increasingly dominated by larger vertebrate feeders, granivores and frugivores as Noisy Miner abundance increased. The mean body size and bill length of the insectivore species present at a site increased with Noisy Miner abundance. This change in the bird community along with reduced diversity in foraging strategies implies a loss of the ecological functions provided by smaller‐bodied species, potentially affecting plant dispersal and regeneration, insect herbivory and ultimately woodland resilience. Our study demonstrates a substantial shift in ecological profile over a broad geographical area as a result of a single native species.     

Foraging and feeding ecology of Platanista: an integrative review

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红头长尾山雀繁殖生态的研究

在安徽合肥紫蓬山区,对红头长尾山雀的繁殖生态进行了系统的观察,并研究了雏鸟的生长特征。研究表明,红头长尾山雀自3月中旬以后开始发情,3月下旬开始营巢,巢位于杉树枝下,球形侧开口或侧顶开口。4月初产卵,每窝平均产6．25枚卵,孵化期为15—16d,孵化率为88％。育维期15—16d,22维全部成活到离巢,雏成活率达100％。体重、翅、嘴峰、跗跖、第5枚初级飞羽和尾羽等形态学参数适合用Logistic曲线方程拟合,拟合参数中,嘴峰的拐点最小,飞羽、翅和尾羽的增长率较高,表明与取食有关的形态优先发育,与飞行有关的形态则在后期发育较快。     

Reproductive ecology of the boreal riparian guild of Drosophila

The reproductive ecology of four sympatric Drosophila virths group species (Diptera Drosophilidae) was studied in the field to trace the factors maintaining species isolation There was a high probability of meeting a heterospecific individual belonging to the same species group on the basis of adult spatial occurrence Direct field observations revealed that the males court also females of the foreign species but interspecific courtships do not lead to mating The main mating period among these species lasted only several weeks and the timing of mating periods differed markedlv in the three most common species Reproductive character displacement between species may explain the observed differences in the timing of the mating periods but they could have arisen in the context of other selective pressures than the prevention of interspecific courtships and matings     

Effectiveness of protected areas for bird conservation depends on guild

Aim

Protected areas are key conservation tools intended to increase biodiversity and reduce extinction risks of species and populations. However, the degree to which protected areas achieve their conservation goals is generally unknown for many protected areas worldwide. We assess the effect of protected areas on the abundance of 196 common, resident bird species. If protected areas were beneficial to avian biodiversity, we expect landscapes with a higher proportion of protected areas will have higher densities of species compared to landscapes with no protection.

Location

Greater Gauteng region, South Africa.

Methods

We analysed bird survey data collected over regular grid cells across the study area. We estimated bird abundance in relation to the proportion of a grid cell that was protected with the Royle–Nichols model and fitted the model once for each of the species. We examined variation in estimated abundance as a function of avian guild (defined by the type of food a species preferentially ate and its foraging mode) with a regression tree analysis.

Results

Abundance was significantly positively related to the proportion of protected areas in grid cells for 26% of the species, significantly negatively related in 15%, and not significantly related in 59% species. We found three distinct guild groups which differed in their average abundance, after accounting for associated variance. Group 1 consisted of guilds frugivores, ground‐feeders, hawkers, predators, and vegivores and average abundance was strongly positively related to the proportion of protected areas. Group 2 included granivores, and average abundance was strongly negatively related to proportion of protected areas. Group 3 included gleaners only, and average abundance was not related to proportion of protected areas.

Main conclusion

We conclude that the network of protected areas within the greater Gauteng region sustained relatively higher abundances of common birds and thus perform an important conservation role.

     

Long-term dynamics of a tropical savanna bird community

Complete two-month censuses of diurnal raptors and strip transect counts of other bird species were compared between 1968–1972 and 1996 to assess changes in the bird community of a 2700ha guinean savanna in Ivory Coast. Among 117 non-raptor species recorded at least once on the transects, 25 mostly uncommon species were absent in 1996 (but only two of them were likely to be extinct in the study area), 4 were first seen in 1996, 14 decreased and 4 increased significantly. All six large forest raptors and resident savanna eagles disappeared before the mid-1980s. Among the 12 remaining breeding raptors, 4 species increased (including the 2 seasonal migrants), 4 species remained stable (including the 2 forest accipiters) and 4 species decreased, but not significantly (including the 2 largest taxa). All 14 non-breeding raptors (Palearctic and African migrants) remained stable or increased. With on average 63 breeding pairs per 1000ha, this area still supports one of the highest densities of diurnal raptors ever recorded. The geographic distributions, seasonal movements and ecological requirements of species involved suggest the most likely origin of specific changes observed. They were attributed, in roughly similar proportion, to: (i) decreasing rainfall (southward shifts leading to appearance or increase of some resident or migrant species); (ii) deforestation, agricultural development and hunting pressure around the reserve (extinction of larger species following habitat fragmentation or degradation, increase of some species); and (iii) habitat modifications inside the reserve (increasing tree cover, invasion of dense thickets, illegal exploitation of palms). The overall community of this small protected area, however, exhibited a remarkable stability during the last 30 years, in spite of dramatic habitat changes outside its limits.     

Indigenous tropical ecology

Two major works on the ecology of Sumatra and Sulawesi two of the world's great tropical islands, have appeared relatively recently. These volumes represent the rarest of genres in tropical ecology: works of indigenous origin with an indigenous audience in mind. An examination of these exciting books prompts us to examine a wider literature on tropical ecology.     

Foraging ecology of the red-crowned parakeet (

The diet of red-crowned parakeets (Cyanoramphus novaezelandiae novaezelandiae) and yellow-crowned parakeets (C. auriceps auriceps) was compared on Little Barrier Island, New Zealand between 1986 and 1987. Significant dietary differences were observed in these sympatric, congeneric species. Yellow-crowned parakeets ate significantly more invertebrates than red-crowned parakeets, which fed on a greater variety of plant foods. Red- crowned parakeets were found in all vegetation types depending on the availability of food and were commonly seen foraging on the ground in open habitats. In contrast, yellow-crowned parakeets were more arboreal and showed distinct preferences for forested habitats. The existence of both parakeet species in sympatry is examined as is the ecological importance of invertebrate food sources. Observed differences in the behaviour and ecology of parakeet species on Little Barrier Island are used to provide insight into the present day distribution and status of parakeets on mainland New Zealand.     

Effects of food supplementation on a tropical bird

Tropical birds typically exhibit a ‘slow pace of life’ relative to higher latitude species. This is often manifested as slow development, low fecundity, and high survival. Following from this, it is predicted that tropical birds may be more likely to trade current reproductive effort to favor self-maintenance, thus supporting survival and future reproduction. To test this idea, we conducted two food supplementation experiments on tropical rufous-collared sparrows (Zonotrichia capensis) in the eastern Andes of Ecuador. In the first experiment, we food-supplemented pairs during the non-breeding life-history stage, and in the second experiment, we food-supplemented pairs that were provisioning fledglings. In both experiments, a larger proportion of food-supplemented birds exhibited pre-basic molt (replacement of feathers) than in a control group. To our knowledge, this is the first study to experimentally demonstrate that a food-supplemented bird invests extra resources into molt, a form of self-maintenance, and contrasts with the majority of food supplementation studies in high latitude birds that show they typically advance the initiation of, or extend the period of, reproduction. Our results are consistent with the syndrome of the slow pace of life in the tropics and support the concept of fundamental differences between temperate-zone and tropical birds.     

Mechanisms regulating bird predation on a herbivorous Larva guild in boreal coniferous forests

Bird predation was previously found to considerably reduce the abundance of the herbivorous insect larva guild feeding on bilberry Vacanium myrtillus within boreal coniferous forests In this follow-up study, interest was focused on determining whether female pied flycatchers Ficedula hypoleuca tend to use the field layer more frequently than other types of feeding niches In addition, the degree to which the conspicuousness of a larva increases the risk of its being preyed upon by birds was evaluated in order to further understand the mechanisms regulating the bird predation effect Larval predation risks were measured by presenting larvae with contrasting characteristics to seven captured female flycatchers
Female flycatchers hunted more frequently in the tree and field layers than in the air However, the relative degree of utilization of the tree and field layer varied considerably between years, with use of field layer being positively related to the abundance of insect larvae on bilberry
Large larvae did not suffer higher bird predation than small larvae when both size classes were presented to the birds on bilberry Larvae that crawl on leaves and stems during feeding (high degree of exposure) were preyed upon more than larvae that feed between leaves they have spun together (low degree of exposure) No difference in larval predation risk was found between sawflies and geometrids, the two taxa represented in the exposed feeder group However, dark geometrids suffered higher predation than green sawflies and green geometrids
My findings suggest that the herbivorous larva guild constitutes an abundant food resource frequently utilized by small bird predators However, certain members of the guild appeared to be preyed upon more than other members Thus the risk for predation seems to be highest for dark geometnds followed in decreasing order by green geometrids. sawflies pyralids, and tortricids     

Seasonal dynamics of guild structure in a bird assemblage of the central Monte desert

Most studies of ecological guilds consider guild membership as a fixed attribute of species, and the guild structure as a fixed attribute of a community. Consequently, almost no study tackled the examination of temporal changes in the guild structure of a particular assemblage. We used data on foraging patterns of central Monte desert birds to assess seasonal differences in resource use by resident species, and to examine seasonal changes in the guild structure of the assemblage. From 1993 until 1999, we quantified the use of foraging substrates, manoeuvres, and height strata, and the utilisation of plants by 18 bird species. Resident species showed different kinds of seasonal dynamics, from no noticeable to drastic changes in their foraging patterns. Seasonal changes in guild structure were remarkable. Only two guilds were present all year round (ground foragers and foliage foragers), although they suffered important species turnover. Three other guilds had a seasonal occurrence: graminivores (during the non-breeding season), arboreal herbivores, and aerial feeders (during the breeding season). Two species changed from one guild to another between seasons. Both presence–absence of migrant species, and changes in the feeding ecology of resident species had an influence on the temporal dynamics of guild structure. These factors appeared to be related with changing resource availability, especially with the birds’ ability for facing lean conditions through migration and with the opportunistic use of seasonally superabundant resources. Our results undermine the trust in studies in which guild structure was assessed irrespective of temporal variations. We show also that guild membership is not a fixed attribute of a species: we should rather evaluate the individuals’ resource use in a given moment to assign them to a guild, instead of obtaining a single measure purporting to represent a species’ fixed attribute.     

Nitrite-oxidizing bacteria guild ecology associated with nitrification failure in a continuous-flow reactor

Nitrification is an important process for nitrogen removal in many wastewater treatment plants, which requires the mutualistic oxidation of ammonia to nitrate by ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). However, this process can be quite unpredictable because both guilds are conditionally sensitive to small changes in operating conditions. Here, dynamics are examined within the NOB guild in two parallel chemostats operated at low and high dilution rates (0.10 and 0.83 day(-1), respectively) during periods of varying nitrification performance. NOB and AOB guild abundances and nitrogen-oxidation efficiency were relatively constant over time in the 0.10 day(-1) reactor; however, the 0.83 day(-1) reactor had two major disturbance episodes that caused destabilization of the NOB guild, which ultimately led to nitrification failure. The first episode caused the extinction of Nitrospira spp. from the system, resulting in chronic incomplete ammonia oxidation and nitrite accumulation. The second episode caused complete loss of nitrification activity, likely resulting from metal toxicity and the previous extinction of Nitrospira spp. from the system. These results exemplify the types of changes that can occur within the NOB guild that result in process impairment or failure, and provide one possible explanation for why nitrification is often unstable at higher dilution rates.     

Foraging niche dynamics and overlap in a guild of passerine birds in a south Swedish coniferous woodland

Summary Three foraging niche dimensions were measured at four seasons in six passerine bird species in a pine-dominated woodland. Total niche size increased in the order Certhia familiaris. In the first two species niche sizewas relatively constant at all seasons in spite of fluctuations in separatedimensions suggesting intraspecific complementarity between dimensionbreadths. Diffuse niche overlap was much lower in summer than at otherseasons in all species. Generally, this was due to movements of exploitationcurves along resource axes away from zones of interspecific overlap andto enlargement of total guild niche size, rather than to a reduction in totalniche size of the species. In some species a positive correlation was indicatedbetween breadth of niche dimension and diffuse overlap in the same dimension.Total niche size was correlated with total diffuse overlap up to acertain overlap value. Interspecific niche size complementarity was stronglysuggested by total guild niche being much less variable between seasons thanthe separate niche size of each species. The narrow niche of P. major, usuallyregarded a generalist, may be due to it being primarily adapted to broadleavedrather than coniferous woodland.     

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.     

Influence of social status on individual foraging and community structure in a bird guild

We investigated the influence of social interactions on individual foraging behavior and community structure of frugivorous birds in southern Costa Rica. Detailed observations of large, heterospecific feeding assemblages at fruiting trees revealed the existence of an interspecific dominance hierarchy, largely consistent with body and bill size. Social status influenced access to food in several ways. First, subordinate species were interrupted more and tended to have shorter foraging bouts than dominant species (n > 1.000 abouts). Second, analysis of over 7,000 videotaped head movements showed that subordinate species spent a smaller fraction of their foraging bouts actually feeding (as opposed to looking about) than did dominants. Third, when many birds were in a tree simultaneously, the foraging bouts of subordinate species were shortened; this effect was less pronounced or absent for species higher in the dominance hierarchy. Fourth, subordinate species foraged less frequently in mixed-species assemblages than did dominant species. Finally, subordinate species fed disproportionately more in the late afternoon at fruiting trees. The influence of social status appeared to manifest itself at the community level. The species composition of foraging assemblages was compared at isolated fruiting trees situated in an agricultural landscape near to (< 0.5 km) and far from (> 6 km) a large tract of primary forest. Whereas the full complement of avian frugivores foraged at the near trees, visitors to the far trees were predominantly of high social status. We discuss reasons why high social status and associated traits might confer an advantage in exploiting human-dominated habitat.     

Understanding testosterone variation in a tropical lek-breeding bird

Male reproductive coalitions, in which males cooperate to attract females, are a rare strategy among vertebrates. While some studies have investigated ultimate aspects of these relationships, little is known about the mechanistic role that hormones play in modulating cooperative behaviours. Here, we examined male testosterone variation in a tropical lekking bird, the wire-tailed manakin (Pipra filicauda), which exhibits cooperative male-male display coalitions. We found that testosterone levels in territorial males were comparable to those of temperate breeding birds, a surprising result given their environmental, social and reproductive dynamics. In addition, social status rather than plumage was a strong predictor of testosterone variation. Territorial males had significantly higher testosterone levels than did two other plumage classes of floater males, who do not hold territories. We hypothesize that testosterone variation plays an important role in the establishment of male dominance hierarchies (competition), while concurrently facilitating stable display partnerships (cooperation).     

Storms drive altitudinal migration in a tropical bird

Although migration is a widespread and taxonomically diverse behaviour, the ecological factors shaping migratory behaviour are poorly understood. Like other montane taxa, many birds migrate along elevational gradients in the tropics. Forty years ago, Alexander Skutch postulated that severe storms could drive birds to migrate downhill. Here, we articulate a novel mechanism that could link storms to mortality risks via reductions in foraging time and provide, to our knowledge, the first tests of this hypothesis in the White-ruffed Manakin (Corapipo altera), a small partially migratory frugivore breeding on the Atlantic slope of Costa Rica. As predicted, variation in rainfall was associated with plasma corticosterone levels, fat stores, plasma metabolites and haematocrit. By collecting data at high and low elevation sites simultaneously, we also found that high-elevation residents were more adversely affected by storms than low elevation migrants. These results, together with striking temporal capture patterns of altitudinal migrants relative to storms, provide, to our knowledge, the first evidence that weather-related risks incurred by species requiring high food intake rates can explain altitudinal migrations of tropical animals. These findings resolve conflicting evidence for and against food limitation being important in the evolution of this behaviour, and highlight how endogenous and exogenous processes influence life-history trade-offs made by individuals in the wild. Because seasonal storms are a defining characteristic of most tropical ecosystems and rainfall patterns will probably change in ensuing decades, these results have important implications for understanding the ecology, evolution and conservation of tropical animals.     

Foraging ecology and audition in echolocating bats

The types of echolocation signal and the auditory capacities of echolocating bats are adapted to specific acoustical constraints of the foraging areas. Bats hunting insects above the canopy use low frequencies for echolocation; this is an adaptation to prey detection over long distances. Bats foraging close to and within foliage avoid masking of insect echoes by specializing on 'fluttering target' detection. 'Gleaning' bats are adapted to the auditory detection of very faint noises generated by ground-dwelling prey, and are capable of analysing fine changes in the echo spectrum, which may indicate a stationary prey changing its posture on a substrate. This review of recent research demonstrates that, in bats, foraging ecology and audition are intricately interrelated and interdependent.