Archive for February, 2007
dukenews.duke.edu
Durham, N.C. — In findings that may offer insight into how evolution operates, a Duke University evolutionary ecologist reported evidence that aggressive male western bluebirds out-compete less aggressive males for preferred breeding territories. In the process, she found that more-aggressive and milder mannered birds also tended to breed in different settings that favor different body types.This study, conducted by Renée Duckworth, suggests the birds may play more active roles in their own natural selection than traditional models of evolution would support.
“The traditional view of evolution is that organisms are passive creatures on which natural selection operates,” said Duckworth, who just completed her doctoral training at Duke. But her research results, published online on Wednesday, April 12, 2006, in the journal Proceedings of the Royal Society B, suggest a different model, at least among these bluebirds.
“By selecting the environment in which they live, animals can actively affect the natural selection they experience,” Duckworth said in an interview. “The main message of this study is that the ability of organisms to choose their environment needs to be made a more explicit part of evolutionary theory.”
In her studies, funded by the National Science Foundation, Duckworth followed up on previous findings that adult western bluebirds aggressively defend large breeding territories and also use different foraging strategies in wooded and open habitats.
In gathering worms and insects to feed their young, birds living in wooded environments “mainly forage by perching on trees to scan the ground for prey,” Duckworth said in her article. But in open areas with few trees, the birds must be agile in order to “hover or hop along the ground to search for prey.”
Despite such advance knowledge about behavior, “the relative importance of behavior in driving or inhibiting evolutionary change remains largely unresolved,” Duckworth said. At the same time, aggressive behavior “has a great potential to affect selection pressures since aggression is known to play a role in securing breeding territories,” she added.
So Duckworth set out to investigate the evolutionary consequences of aggression, selecting western bluebirds as her study animal. Western bluebird males prefer to breed in territories with more than one nest available. And they readily accept human-made nest boxes as substitutes for the hollowed out cavities they occupy in the wilds.
On a ranch in Montana, Duckworth created a breeding ground by setting out nest boxes to attract the birds. In addition, she purposely manipulated the densities of the nest boxes, putting two rather than one in some territories in order to test whether more-aggressive males were better at acquiring territories with multiple nests.
Duckworth measured each male’s aggressiveness by observing its response to a tree swallow that she placed near a nest box. Tree swallows are a rival species known to compete with bluebirds for nesting spaces in the wilds. In order to avoid injury to the birds, she enclosed the swallows in cages placed near individual nest boxes. She observed the bluebirds’ reactions from a nearby blind.
She found that when she manipulated the densities of nest boxes prior to the birds’ arrival at the breeding ground, more-aggressive males did, indeed, acquire territories with multiple boxes. But when she manipulated the densities after the birds already had settled on territories, the responses of more- and less-aggressive males did not differ.
“Taken together, these experiments show that, first, aggression plays a key role in determining the outcome of territorial interactions, and, second, male aggression is set before they ever get to their territories,” Duckworth said. “These results support my previous findings that males are highly consistent in their aggressive behavior and can be categorized as either aggressive or nonaggressive.”
Duckworth also evaluated western bluebird aggression in more realistic settings by installing nest boxes near natural breeding cavities to duplicate natural breeding territory densities.
She found that open areas had higher densities of nest cavities and that more aggressive male birds were preferentially attracted to these areas. Moreover, bigger males with longer legs and tails living in the open habitats produced more offspring.
Do the results of these tests mean that western bluebirds are diverging into two different species due to behavioral interactions that sort males into different environments — one favoring open environments and the other tree cover?
“If the sorting of aggressive and nonaggressive males into different habitats is consistent over time, then it could set the stage for ecological divergence,” Duckworth said.
But such a divergence seems unlikely, she said, because the frequency of highly aggressive western bluebird males can shift or even diminish over the years.
“This should allow more nonaggressive males to spread into open habitats,” she said. “Another factor is that an environment itself is always changing,” as fires, pests and weather remake western bluebirds’ surroundings. Consequently, the link between behavior and settlement patterns is dynamic and ever-changing.
“This study does suggest that behavior can play a leading role in evolutionary processes,” Duckworth said. She plans to follow up with a study investigating whether differences in aggression among male western bluebirds have underlying genetic differences that have the potential to evolve.
February 12th, 2007
geocities.com
Few people realize that we share our school campus with a wide variety of native wildlife. Have you noticed two inconspicuous bowls of mud plastered to the corner of the roof in front of the lobby? These are the nests, one apparently abandoned, of a pair of Pacific swallows, a common bird in Taiwan. These swallows have nested outside our lobby, undisturbed by people, and have cared for their fledglings successfully for many years. Unfortunately this golden opportunity for educating children has been for the most part overlooked.
   Of the 42 species of birds found on the TAS campus, Pacific swallows are one of the most easy to observe because they are often surprisingly fearless of humans; they dart into crowds during school fairs and dodge the busy traffic on the roads. Pacific swallows are small birds, about 13 cm long and have a glossy, dark blue back, grayish belly, and slightly forked tail. Their face is orange with a dark band across their eyes.
   Although studies show that these birds normally breed between April and June, the pair at our school seem to be actively breeding into July, when their young finally leave the nest. Beginning in April or May, the parent birds begin tidying up their nest made of mud, straw, and feathers. Then the eggs are then laid and incubation begins. After the chicks hatch, both parents busy themselves feeding the four — usually — hungry mouths. The parents cruise gracefully through the air, snapping up airborne insects, returning to the nest, and stuffing the insects into the mouth of the chick who is begging the loudest and whose mouth is opened the widest. The feeding is amazing to watch because the adults often do not land when they feed the chicks; the whole process only takes a split second. Since pacific swallows breed during the summer, most students cannot observe their breeding behavior. However, during the school year the swallows are never far from campus, and teachers can take their students to observe them and their unused nests. When not perched on top of the glass wall of the lobby, the swallows often fly around the parking lots or the athletic fields. Occasionally they perch outside classroom windows, where they can be observed at close range.
   Our school is privileged to have these swallows nest outside the lobby, but these birds must be protected. Although their nests the second floor roof are safely out of reach, the swallows are not totally secure from harassment or excessively loud noise; they and their young are especially susceptible to disturbance during breeding season. Most importantly, any action that might disturb the nests or any intention to remove them should be thoroughly reviewed by the entire school community.
February 9th, 2007
ncbi.nlm.nih.go
Brown CR, Brown MB.
Department of Biological Sciences, University of Tulsa
How colonial animals space their nests in relation to conspecifics may provide clues as to whether coloniality provides net benefits or occurs only because breeding sites are limited. We examined how nearest-neighbour distance varied in relation to settlement time in the highly colonial cliff swallow, Petrochelidon pyrrhonota, comparing observed nearest-neighbour distances to those expected if birds spread out to maximize nest spacing. Cliff swallows generally settled closer to each other than required by the available substrate, and clustered their nests closer in large colonies than in small ones. The first settlers at a colony site spaced themselves further apart than later arrivals but did not maximize nearest-neighbour distances. The first arrivals maintained greater nest spacing throughout the season than did birds that arrived later. Colony size and amount of nesting substrate had no effect on initial settlement distances of the first arrivals, but eventual nearest-neighbour distances declined with colony size. First arrivals may gain less from nesting with conspecifics and thus are less likely to cluster their nests than later arrivals, which may often be young or naive birds that gain more from the social benefits of colonial nesting. The results are consistent with the presumed social advantages cliff swallows receive from coloniality and do not support the hypothesis that colonies result from nesting site limitation. Copyright 2000 The Association for the Study of Animal Behaviour.
PMID: 10640366 [PubMed - as supplied by publisher]
February 8th, 2007
.pnas.org
DW Winkler and FH Sheldon
Nest construction is more diverse in the Hirundinidae than in any other family of oscine birds. To explore the evolution of this diversity, we superimposed nest data on a DNA-hybridization phylogeny of 17 swallow species. Nest construction is tightly linked to the inferred evolutionary history. Burrowing appears to be the primitive nesting mode, and burrowing ancestors gave rise to cavity-adopting and mud-nesting clades. Obligate cavity adoption is mostly confined to a monophyletic clade in the New World, and the diversification of obligate nest adopters appears to be tied to the richness of forest habitats and recent active mountain building there. Construction of mud nests originated only once in the history of the group, and mud-nesters have diversified principally in Africa, where a drier climatic history has favored their mode of nesting. The use of pure mud to construct a hanging nest is unique among all birds, and we infer that mud nests have increased in complexity during evolution from simple mud cups to fully enclosed retort-shaped nests. This increased complexity appears to have been the critical precursor for the evolution of high-density colonial mud-nesters.
February 7th, 2007
3000 m (high)
(9840 ft)
animaldiversity.ummz.umich.edu
Barn swallows are very adaptable birds and can nest anywhere with open areas for foraging, a water source, and a sheltered ledge. They seek out open habitats of all types, including agricultural areas, and are commonly found in barns or other outbuildings. They will also build nests under bridges, the eaves of old houses, and boat docks, as well as in rock caves and even on slow-moving trains.
Physical Description
Barn swallows are small birds. They range in size from 14.6 to 19.9 cm long, with a wingspan of 31.8 to 34.3 cm. They weigh between 17 and 20 g. Barn swallows are metallic blue-black above and pale beige below. They have light brown on their throat and forehead, and have a long, deeply-forked tail. Males and females are similar in appearance, though females tend to be less vibrantly colored and have shorter outer tail-streamers.
Asymmetry of physical characteristics in barn swallows tends to be transmitted to the young in distinct parent to offspring patterns. Tail asymmetry tends to pass from father to son and from mother to daughter. Alternatively, wing asymmetry does not appear to transfer at all on a reliable basis from parent to offspring.
Reproduction
Barn swallows are socially monogamous. However, extra-pair copulations are common, making this species genetically polygamous. Breeding pairs form each spring after arrival on the breeding grounds. Pairs re-form each spring, though pairs that have nested together successfully may mate together for several years. Males try to attract females by spreading their tails to display them and singing.
Several studies have researched sexual selection in barn swallows. Moller (1994) documented female barn swallows selecting for symmetrical wings and tails in potential mates. Males exhibiting greater symmetry acquired mates more quickly than did asymmetric males. Asymmetry can result from genetic factors such as inbreeding or mutations as well as from environmental stress such as food deficiency, parasite infestation, or the presence of pathogens. Moller observed that individuals affected by these factors not only exhibited asymmetry, but also decreased strength and longevity. Therefor, females that selected symmetrical mates would presumably be selecting superior mates. In addition to selecting for symmetry, females also tend to select males with longer tail feathers. Moller observed a connection between the tail length of male barn swallows and their offspring’s vitality and longevity. Males with longer tail feathers exhibit traits of greater longevity which is passed on to their offspring. Females thus gain an indirect fitness benefit from this form of selection, as longer tail feathers indicate a genetically stronger individual who will produce offspring with enhanced vitality. Individuals with longer tails have also been observed to demonstrate greater disease resistance than their short-tailed counterparts. There is also evidence that males select female mates with long tails.
Unmated adults often associate with a breeding pair for up to an entire season. Though these “helpers” do not usually feed the young, they may help with nest defense, nest building, incubation and brooding. “Helpers” are predominantly male, and may succeed in mating with the resident female, leading to polygyny. (Bolzern, Moller, and Saino, 1997; Brown and Brown, 1999; De Lope and Moller, 1993; Moller, 1993; Moller, 1994a; Moller, 1994b)
Barn swallows usually breed between May and August, but this varies greatly with location. They usually raise two broods of chicks each summer. Both birds of a pair make the nest. They build the shell of mud, and line it with grass and feathers. The female lays 3 to 7 eggs (average 5). Both parents incubate the eggs, which hatch in 13 to 15 days. The chicks are naked and helpless when they hatch. Both parents feed and protect the chicks, as well as removing fecal sacs from the nest. The nestlings remain in the nest for about 20 days before fledging. When barn swallows are handled by humans they tend to attempt to fledge at least a day too early. The parents continue to care for the chicks for up to a week after fledging, feeding them and leading them back to the nest to sleep. By two weeks after fledging, the barn swallow chicks have dispersed and often travel widely to other barn swallow colonies. Young barn swallows are able to breed in the first breeding season after they have hatched. Generally, young barn swallows do not produce as many eggs as do older birds. (Brown and Brown, 1999; McWilliams, 2000; Perrins, 1989; Terres, 1980)
February 6th, 2007
bioone.org
K. E. H. AitkenA, K. L. WiebeB, K. MartinA, C,
A. Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver,British Columbia V6T 1Z4, Canada, B. Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada, C. Canadian Wildlife Service, 5421 Robertson Road, RR1, Delta, British Columbia V4K 3N2, Canada
Abstract
Most obligate cavity-nesting birds are considered to be nest-site limited, either by time or energy to excavate or to acquire suitable holes for nesting. We examined rates of nest-cavity reuse for a rich community of cavity-nesting birds in mixed forests in interior British Columbia. Using a sample of 402 cavity-reuse cases over five years, we measured cavity reuse for 20 cavity-nesting bird and mammal species (three guilds), and examined the relationship between nest-cavity reuse and features of cavities, nest trees, and forest stands. Eight percent of used cavities were destroyed between years. Reuse rates were 17% for the cavities of weak excavators such as nuthatches and chickadees, 28% for formerly active woodpecker nests, and 48% for cavities previously used by secondary cavity nesting birds, but there was considerable species variation within all guilds. Nest cavities in aspen that were deep with large entrances had the highest reuse. At the forest stand level, cavities in trees close to edges and in sites with more edge habitat had greater reuse. Reused cavities tended to be occupied in sequential years rather than being inactive for a year. With increasing amounts of managed landscapes, availability of suitable cavities for forest nesting vertebrates is decreasing. Reuse of existing cavities might help mitigate the problem of nest-site limitation.
Resumen
La plupart des oiseaux nichant obligatoirement en cavité sont considérés comme étant limités quant à leur site de nidification, soit pour une question de temps ou d’énergie qui sont nécessaires pour creuser ou acquérir des trous adaptés à leur nidification. Nous avons examiné les taux de réutilisation de cavités de nidification pour une communauté riche en oiseaux nichant dans des cavités et dans des forêts mixtes de l’intérieur de la Colombie Britannique. En utilisant un échantillon de 402 cas de cavités réutilisées, nous avons mesuré la réutilisation de cavités pour 20 espèces d’oiseaux et de mammifères nichant dans des cavités (trois guildes), et examiné la relation entre la réutilisation de cavité de nidification et les caractéristiques des cavités, des arbres utilisés pour la nidification, et des peuplements forestiers. 8% des cavités utilisées ont été détruites au cours des années. Les taux de réutilisation étaient de 17% pour les cavités des espèces à faible capacité de creusage telles que les sittelles et les mésanges, 28% pour les nids de pics anciennement utilisés, et 48% pour les cavités précédemment utilisées par des oiseaux nichant dans des cavités de manière secondaire, mais il y avait une variation considérable entre les espèces a l’intérieur de toutes les guildes. Les cavités de nidification profondes, avec de larges entrées, et situées dans les trembles avaient le plus haut taux de réutilisation. Au niveau du peuplement forestier, les cavités des arbres proches des lisières et dans les sites riches en habitats de lisière ont connu une plus grande réutilisation. Les cavités réutilisées tendaient à être occupées durant des années consécutives au lieu d’être inactives pour une année. Avec une quantité croissante de paysages aménagés, la disponibilité de cavités adaptées à la nidification forestière des vertébrés diminue. Le réutilisation de cavités existantes pourrait aider à atténuer les problèmes de limitation des sites de nidification.
February 2nd, 2007
sabah.gov.my
Laurentius N. Ambu
Deputy Director Sabah Wildlife Department Kota Kinabalu ABSTRACT
The two most economically-important swiflets are the so-called edible nest swiflets: the white-nest swiflets (Aerodramus fuciphagus) and the Black-nest swiflet (Aerodramus maximus). Both species occur in Sabah. With the dwindling edible-nest swiflets population due to effects of increased harvesting pressure and effects of forest habitat modifications, new dimensions need to be embarked to invigorate the conservation of these swiflets population while at the same time enhance the production of the edible birds nest vis-à -vis the sustainable development of the bird nests industry in Sabah. It is therefore timely to venture new avenues towards this end. From the case studies on swiflet farming in Indonesia and Malaysia, the potential contribution of bird nests produced from swiflet farms is enormous. With the right bird houses, technology and well – manipulated environmental regimes, it is now possible to produce edible bird nests from farm houses. From the experience above, it is hoped that commercial farming of swiflet in Sabah is realised.
February 1st, 2007
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