Bird diversity in cacao farms and forest fragments of western Panama

Theobroma cacao plantings, when managed under the shade of rainforest trees, provide habitat for many resident and migratory bird species. We compared the bird diversity and community structure in organic cacao farms and nearby forest fragments throughout mainland Bocas del Toro, Panama. We used this dataset to ask the following questions: (1) How do bird communities using cacao habitat compare to communities of nearby forest fragments? (2) To what extent do Northern migratory birds use shaded cacao farms, and do communities of resident birds shift their abundances in cacao farms seasonally? (3) Do small scale changes in shade management of cacao farms affect bird diversity? Using fixed radius point counts and additional observations, we recorded 234 landbird species, with 102 species that were observed in both cacao and forest fragments, 86 species that were only observed in cacao farms, and 46 species that were restricted to forest fragments. Cacao farms were rich in canopy and edge species such as tanagers, flycatchers and migratory warblers, but understory insectivores were nearly absent from cacao farms. We observed 27 migratory species, with 18 species in cacao farms only, two species in forest only, and seven species that occurred in both habitats. In cacao farms, the diversity of birds was significantly greater where there was less intensive management of the canopy shade trees. Shade tree species richness was most important for explaining variance in bird diversity. Our study shows that shaded cacao farms in western Panama provide habitat for a wide variety of resident and migratory bird species. Considering current land use trends in the region, we suggest that action must be taken to prevent conversion away from shaded cacao farms to land uses with lower biodiversity conservation value.     

Effect of cooling rates on the cold hardiness and cryoprotectant profiles of locust eggs

To examine the relationship between cooling rate and cold hardiness in eggs of the migratory locust, Locusta migratoria, the survival rates and cryoprotectant levels of three embryonic developmental stages were measured at different cooling rates (from 0.05 to 0.8 degrees C min(-1)) in acclimated and non-acclimated eggs. Egg survival rate increased with decreasing cooling rate. The concentration of cryoprotectants (myo-inositol, trehalose, mannitol, glycerol, and sorbitol) increased in non-acclimated eggs, but varied significantly in response to different cooling rates in acclimated eggs. The acclimation process (5 degrees C for 3 days) did not increase eggs resistance to quick cooling ("plunge" cooling and 0.8 degrees C min(-1)). Earlier stage embryos were much more sensitive than later stage embryos to the same cooling rates. Time spent at subzero temperatures also had a strong influence on egg survival.     

Magnetic versus celestial cues: cue-conflict experiments with migrating silvereyes at dusk

To assess the relative importance of celestial and magnetic cues for orientation at dusk, Australian silvereyes, Zosterops l. lateralis, were subjected to artificial magnetic fields under the natural evening sky, beginning 30 min before sunset. Control birds tested in the local geomagnetic field preferred their normal south-southwesterly migratory direction. Birds tested in a magnetic field with north deflected counterclockwise to 240°WSW showed northeasterly tendencies from the first test onward. Birds subjected to a corresponding clockwise deflection to 120°ESE, in contrast, first showed southerly directions, but from the 7th test onward shifted towards the northwest. Hence, both experimental groups followed the shift in magnetic north, one immediately, the other after a delay. When the birds were later tested in a vertical magnetic field without directional information, the two experimental groups continued in the direction they had preferred in the artificial magnetic fields, presumably by celestial cues alone. This indicates that they had not simply ignored celestial cues, but had recalibrated them according to the altered magnetic fields. The reasons for the initial difference between the two experimental groups remain unclear. Delayed responses to deflections of magnetic north have also been observed in previous studies. They appear to be the main reason why studies that expose birds only once to a cue-conflict situation often seem to indicate a dominance of celestial cues, whereas studies exposing the birds repeatedly usually indicate a dominance of magnetic cues. Accepted: 17 September 1997     

鄱阳湖都昌候鸟自然保护区丰水期和枯水期鸟类多样性

2009年12月和2010年5月,利用样线法和同步调查法对江西省鄱阳湖都昌候鸟自然保护区的鸟类开展了调查,分析了丰水期和枯水期鸟类群落结构的特征及其差异.野外调查共记录到鸟类14目43科169种.丰水期鸟类有36科96种,枯水期鸟类36科135种.其中,国家重点保护鸟类17种.结合保护区日常监测到白鹤(Grus leucogeranus)、灰鹤(G.grus)、白头鹤(G.monacha)和白枕鹤(G.vipio)的分布记录,该保护区鸟类累计达173种.保护区枯水期鸟类以雀形目、鹆形目和雁形目为主,分别占枯水期鸟类种类总数的47.4％、13.3％和9.6％;丰水期鸟类以雀形目、鸻形目和鹳形目为主,分别占鸟类种类总数的58.3％、8.3％和10.4％.枯水期和丰水期鸟类物种组成存在明显的季节性变换.枯水期农田生境鸟类多样性最高,其次是草洲、沼泽和水体,泥滩生境鸟类多样性最低;丰水期农田和水体生境鸟类多样性基本相同.都昌候鸟自然保护区枯水期的优势种为八哥(Acridotheres cristatellus)、白头鹎(Pycnonotus sinensis)、灰椋鸟(Sturnus cineraceus)、麻雀(Passer montanus)和山斑鸠(Streptopelia orientalis),丰水期为白鹭(Egretta garzetta)和八哥.     

Magnetite-based magnetoreception: the effect of repeated pulsing on the orientation of migratory birds

Previous studies have shown that a magnetic pulse affected the orientation of passerine migrants for a short period only: for about 3 days, the birds’ headings were deflected eastward from their migratory direction, followed by a phase of disorientation, with the birds returning to their normal migratory direction after about 10 days. To analyze the processes involved in the fading of the pulse effect, migratory birds were subjected to a second, identical pulse 16 days after the first pulse, when the effect of that pulse had disappeared. This second pulse affected the birds’ behavior in a different way: it caused an increase in the scatter of the birds’ headings for 2 days, after which the birds showed normal migratory orientation again. These observations are at variance with the hypothesis that the magnetite-based receptor had been fully restored, but also with the hypothesis that the input of this receptor was ignored. They rather indicate dynamic processes, which include changes in the affected receptor, but at the same time cause the birds to weigh and rate the altered input differently. The bearing of these findings on the question of whether single domains or superparamagnetic particles are involved in the magnetite-based receptors is discussed.     

迁飞过程中昆虫的行为

根据国内外对昆虫迁飞的雷达观测结果,综述了迁飞过程中昆虫的成层、定向和集聚行为及其生态学意义。昆虫在迁飞过程中不完全是被动地随风飘流,而是在一定程度上自主地选择了自己的运行轨迹。它们选择在气温最高、风力最大和风向最适的高度成层,并通过定向进一步修饰位移方位,从而可最大限度地利用空气动力到达新的栖息地。同时,不同尺度的大气辐合过程使得迁飞昆虫集聚成足以在某种条件下引起局地爆发的高密度种群,而地面大发生种群形成与否取决于大气辐合的发生频率、强度和寿命,以及集聚起来的昆虫是否降落,在何时何地降落,是否还会再迁出等。阐明昆虫在迁飞过程中的各种行为机制是迁飞性害虫测报和防治的关键所在。     

Seasonal and diel transitions in physiology and behavior in the migratory dark-eyed junco

Body mass, fat stores, activities of lipogenic and lipolytic enzymes, and plasma corticosterone were measured throughout seasonal and diel transitions from fall through spring encompassing the non-migratory stages of early and mid winter, the prealternate molt, and the spring migratory stage in captive dark-eyed juncos to determine the physiological mechanisms underlying adaptations for migration. On a seasonal basis, lipid enzymes and corticosterone varied little throughout the stages even though the birds underwent dramatic alterations in mass, fat deposition, behavior, and activation of the reproductive axis. By contrast, diel changes were found in lipogenesis, lipolysis, muscle lipoprotein lipase, and plasma corticosterone when comparing birds in the two phases of spring migration--active flight and resting, as during times of stopover. In these two phases of migration, coordination of the lipogenic and lipolytic systems appear to maximize storage of fatty acids during rest and delivery/utilization during flight. Diel patterns of corticosterone revealed fairly consistent peaks during the night time (23:00) throughout the nonmigratory period. The profile of this pattern altered during the migratory period with variation between the flight and resting phases. In sum, the results from these captive studies offer a new approach for studying the regulation of migratory physiology in free-living birds.     

A role for thyroid hormones in the development of premigratory disposition in redheaded bunting,Emberiza bruniceps

Excessive fat deposition and zugunruhe (nocturnal restlessness), two characteristics of premigratory disposition, are displayed in caged redheaded buntings. In earlier experiments thyroid ablation was found to inhibit premigratory fattening in this bird. Also, seasonal investigations on thyroid hormonal profiles indicated a distinct rise in circulating tri-iodothyronine just before spring migration, most likely as a result of increased peripheral monodeiodination of thyroxine. The physiological relevance of these findings has been assessed in the present paper. Results indicated that removal of thyroid gland completely prevented development of zugunruhe and fat deposition; replacement therapy with T4 or T3 restored both. Thyroxine-induced fattening in thyroidectomized birds was found to be dose responsive. In two experiments in thyroidectomized and intact birds each suppression of extrathyroidal conversion of thyroxine into triiodothyronine by iopanoic acid completely suppressed zugunruhe and fattening in thyroidectomized as well as intact birds, arguing for a role of triiodothyronine in migratory physiology. Blockage of thyroxine to triiodothyronine conversion, however, did not suppress feather regeneration, indicating that unlike effects on migratory parameters in the same individuals thyroxine-induced feather regeneration does not involve prior monodeiodination to triiodothyronine. Thus, contrary to the prevailing view that triiodothyronine alone is the finally active thyroid hormone (thyroxine being a precursor), both thyroxine and triiodothyronine may have specific roles to play in the physiology of seasonal events, and peripheral conversion of thyroxine to triiodothyronine may be one of the physiological devices to ensure that energetically incompatible events like migration and moulting do not occur simultaneously. Results also indicate that increasing spring daylengths which are known to trigger avian migration may influence peripheral conversion of thyroxine to triiodothyronine possibly imparting to this physiological process an adaptive value in the timing of seasonal events.Abbreviations IOP iopanoic acid - NS normal saline - RIA radioimmunoassay - T4 thyroxine - T3 triiodothyronine - Tx thyroidectomized     

Effects of precocene I and II on flight behaviour in Oncopeltus fasciatus, the migratory milkweed bug

Treatment of newly emerged adult Oncopeltus fasciatus with the corpus allatum inhibitors. 7-methoxy-2,2-dimethyl chromene or 6,7-dimethoxy-2,2-dimethyl chromene (preocene I and II) results in an inhibition of long-term flight (presumed migratory) behaviour in both males and females and inhibition of oögenesis in females. Treatment of reproductive females with precocene briefly stimulates flight behaviour (which ceases in such females as oviposition begins) and then subsequently inhibits it. Oviposition also ceases in such females and oöcyte resorption occurs. Topical application or injections of JH III to precocenetreated animals results in immediate restoration of the tendency to make long tethered flights while corpora cardiaca extract injections, corpora cardiaca implantation, sham implantation, sham injections and sham topical applications were ineffective in restoring prolonged flight behaviour to precocene-treated animals.Restoration of flight by JH III injection was observed within 1 hr after treatment with the hormone. These results indicate that JH is necessary for prolonged flight and presumably migratory behaviour in this species and its stimulatory effect on flight behaviour is immediate. Possible mechanisms of action of the hormone on flight behaviour are discussed.     

Why do juvenile fourhorn sculpin, Triglopsis quadricornis, appear in the pelagic habitat at night?

Synopsis Challenging the generally accepted view of the fourhorn sculpin Triglopsis quadricornis as a cold-stenothermal and true benthic species, novel findings of juveniles in the pelagic habitat of Lake Vättern, Sweden, have been examined and critically evaluated. Young-of-the-year and small-sized, sexually mature individuals, ranging 27–45 and 82–110 mm in total length, were recorded in nocturnal trawl catches from pelagic midwater in August. The sculpin had fed extensively on both benthic and semi-pelagic crustaceans, including large cyclopoid copepods, Mysis relicta, Pallasea quadrispinosa, Monoporeia affinis, Gammaracanthus lacustris, and Saduria entomon. Based on an extensive literature review a series of ecological and evolutionary reasons for a pelagic behavior of this profundal coldwater fish is suggested. Nocturnal, semi-pelagic feeding, and consecutive, thermotactic, vertical migrations up in midwater as shown by Wurtsbaugh & Neverman (1988) in order to maximize energy intake after feeding, are possible adaptations of these juvenile sculpin for minimizing size-dependent mortality due to intra- and interspecific predation and competition from other deepwater fishes.