Hummingbirds have a unique way of hover- ing. However, only a few published papers have gone into details of the corresponding three-dimensional vortex struc- tures and transient aerodynamic forces. In order to deepen...Hummingbirds have a unique way of hover- ing. However, only a few published papers have gone into details of the corresponding three-dimensional vortex struc- tures and transient aerodynamic forces. In order to deepen the understanding in these two realms, this article presents an integrated computational fluid dynamics study on the hovering aerodynamics of a rufous hummingbird. The original morphological and kinematic data came from a former researcher＇s experiments. We found that conical and sta- ble leading-edge vortices （LEVs） with spanwise flow inside their cores existed on the hovering hummingbird＇s wing surfaces. When the LEVs and other near-field vortices were all shed into the wake after stroke reversals, periodically shed bilateral vortex rings were formed. In addition, a strong downwash was present throughout the flapping cycle. Time histories of lift and drag were also obtained. Combining the three-dimensional flow field and time history of lift, we believe that high lift mechanisms （i.e., rotational circulation and wake capture） which take place at stroke reversals in insect flight was not evident here. For mean lift throughout a whole cycle, it is calculated to be 3.60 g （104.0 % of the weight support）. The downstroke and upstroke provide 64.2 % and 35.8 % of the weight support, respectively.展开更多
During the 20th century,there has been an ongoing agricultural expansion and global warming,two of the main determinants influencing biodiversity changes in Argentina.The red hocicudo mouse(Oxymycterus rufus)inhabits ...During the 20th century,there has been an ongoing agricultural expansion and global warming,two of the main determinants influencing biodiversity changes in Argentina.The red hocicudo mouse(Oxymycterus rufus)inhabits subtropical grasslands and riparian habitats and has increased its abundance in recent years in central Argentina agroecosystems.This paper describes the long-term temporal changes in O.rufus abundance in Exaltación de la Cruz department,Buenos Aires province,Argentina,in relation to weatherfluctuations and landscape features,as well as analyzes the spatio-temporal structure of captures of animals.We used generalized liner models,semi-variograms,the Mantel test,and autocorrelation functions for the analysis of rodent data obtained from trappings conducted between 1984 and 2014.O.rufus showed an increase in abundance across the years of study,with its distribution depending on landscape features,such as habitat types and the distance tofloodplains.Capture rates showed a spatio-temporal aggregation,suggesting expansion from previously occupied sites.O.rufus was more abundant at lower minimum temperatures in summer,higher precipitation in spring and summer,and lower precip-itations in winter.Weather conditions affected O.rufus abundance,but there was local variation that differed from global patterns of climate change.展开更多
Background:Pine savannas are primarily managed with frequent prescribed fire(≤3 years)to promote diversity of flora and fauna,and to maintain open,park-like conditions needed by species such as the endangered red-coc...Background:Pine savannas are primarily managed with frequent prescribed fire(≤3 years)to promote diversity of flora and fauna,and to maintain open,park-like conditions needed by species such as the endangered red-cockaded woodpecker(Picoides borealis).However,a knowledge gap exists in our understanding of bobcat(Lynx rufus)habitat selection in longleaf pine savannas and research is warranted to direct our future management decisions.Methods:We examined bobcat habitat selection in a pine savanna managed with frequent fires at two spatial scales(i.e.,study area boundary[hereafter,landscape scale])and annual area of use[95%kernel density;local scale],and assessed effects of prescribed fire on bobcat habitat selection.Specifically,we monitored 45 bobcats(16 males and 29 females)during 2001–2007.Results:We found differential habitat selection by sex.At the landscape scale,female bobcats were closer to mixed pine-hardwoods,young pine,and secondary roads,but farther from mature pine and hardwoods stands relative to males.We found no difference in selection of agriculture,shrub-scrub,and primary roads between sexes.At the annual area of use scale,female bobcats were closer to secondary roads,but farther from agriculture and shrub-scrub relative to males.We found no difference in selection of mature pine,mixed pine-hardwoods,hardwoods,young pine,and primary roads between sexes.Bobcats primarily selected for stands burned≤1.1 years post-fire.Conclusions:Our results show that bobcats exploit a broad range of habitat types in pine landscapes managed with frequent fire and commonly use recently burned stands(≤1.1 year post-fire),suggesting prey in many areas of this system are at risk of bobcat predation.Additionally,we suggest land managers consider scale of selection by bobcats when developing habitat management strategies.展开更多
Animals that feed from resources that are constant in space and that refill may benefit from repeating the order in which they visit locations.This is a behavior known as traplining,a spatial phenomenon.Hummingbirds,l...Animals that feed from resources that are constant in space and that refill may benefit from repeating the order in which they visit locations.This is a behavior known as traplining,a spatial phenomenon.Hummingbirds,like other central-place foragers,use short traplines when moving between several rewarding sites.Here we investigated whether traplining hummingbirds also use relevant temporal information when choosing which flowers to visit.Wild rufous hummingbirds that were allowed to visit 3 artificial flower patches in which flowers were refilled 20 min after they had been depleted repeated the order in which they visited the 3 patches.Although they tended to visit the first 2 patches sooner than 20 min,they visited the third patch at approximately 20-min intervals.The time between visits to the patches increased across the experiment,suggesting that the birds learned to wait longer before visiting a patch.The birds appeared to couple the sequential pattern of a trapline with temporal regularity,to some degree.This suggests that there is a temporal component to the repeated spatial movements flown by foraging wild hummingbirds.展开更多
基金financially supported by the Supporting Foundation of the Ministry of Education (Grant 62501040303)the Pre-research Fund (Grants 9140A26020313JW03371, 9140A260204 14JW03412)the New Century Excellent Talents Support Program from the Ministry of Education of China (Grant NCET-10-0583)
文摘Hummingbirds have a unique way of hover- ing. However, only a few published papers have gone into details of the corresponding three-dimensional vortex struc- tures and transient aerodynamic forces. In order to deepen the understanding in these two realms, this article presents an integrated computational fluid dynamics study on the hovering aerodynamics of a rufous hummingbird. The original morphological and kinematic data came from a former researcher＇s experiments. We found that conical and sta- ble leading-edge vortices （LEVs） with spanwise flow inside their cores existed on the hovering hummingbird＇s wing surfaces. When the LEVs and other near-field vortices were all shed into the wake after stroke reversals, periodically shed bilateral vortex rings were formed. In addition, a strong downwash was present throughout the flapping cycle. Time histories of lift and drag were also obtained. Combining the three-dimensional flow field and time history of lift, we believe that high lift mechanisms （i.e., rotational circulation and wake capture） which take place at stroke reversals in insect flight was not evident here. For mean lift throughout a whole cycle, it is calculated to be 3.60 g （104.0 % of the weight support）. The downstroke and upstroke provide 64.2 % and 35.8 % of the weight support, respectively.
文摘During the 20th century,there has been an ongoing agricultural expansion and global warming,two of the main determinants influencing biodiversity changes in Argentina.The red hocicudo mouse(Oxymycterus rufus)inhabits subtropical grasslands and riparian habitats and has increased its abundance in recent years in central Argentina agroecosystems.This paper describes the long-term temporal changes in O.rufus abundance in Exaltación de la Cruz department,Buenos Aires province,Argentina,in relation to weatherfluctuations and landscape features,as well as analyzes the spatio-temporal structure of captures of animals.We used generalized liner models,semi-variograms,the Mantel test,and autocorrelation functions for the analysis of rodent data obtained from trappings conducted between 1984 and 2014.O.rufus showed an increase in abundance across the years of study,with its distribution depending on landscape features,such as habitat types and the distance tofloodplains.Capture rates showed a spatio-temporal aggregation,suggesting expansion from previously occupied sites.O.rufus was more abundant at lower minimum temperatures in summer,higher precipitation in spring and summer,and lower precip-itations in winter.Weather conditions affected O.rufus abundance,but there was local variation that differed from global patterns of climate change.
基金We are grateful for funding provided by the Joseph W.Jones Ecological Research Center at Ichauway,Robert W.Woodruff Foundation,and the Warnell School of Forestry and Natural Resources at the University of Georgia.
文摘Background:Pine savannas are primarily managed with frequent prescribed fire(≤3 years)to promote diversity of flora and fauna,and to maintain open,park-like conditions needed by species such as the endangered red-cockaded woodpecker(Picoides borealis).However,a knowledge gap exists in our understanding of bobcat(Lynx rufus)habitat selection in longleaf pine savannas and research is warranted to direct our future management decisions.Methods:We examined bobcat habitat selection in a pine savanna managed with frequent fires at two spatial scales(i.e.,study area boundary[hereafter,landscape scale])and annual area of use[95%kernel density;local scale],and assessed effects of prescribed fire on bobcat habitat selection.Specifically,we monitored 45 bobcats(16 males and 29 females)during 2001–2007.Results:We found differential habitat selection by sex.At the landscape scale,female bobcats were closer to mixed pine-hardwoods,young pine,and secondary roads,but farther from mature pine and hardwoods stands relative to males.We found no difference in selection of agriculture,shrub-scrub,and primary roads between sexes.At the annual area of use scale,female bobcats were closer to secondary roads,but farther from agriculture and shrub-scrub relative to males.We found no difference in selection of mature pine,mixed pine-hardwoods,hardwoods,young pine,and primary roads between sexes.Bobcats primarily selected for stands burned≤1.1 years post-fire.Conclusions:Our results show that bobcats exploit a broad range of habitat types in pine landscapes managed with frequent fire and commonly use recently burned stands(≤1.1 year post-fire),suggesting prey in many areas of this system are at risk of bobcat predation.Additionally,we suggest land managers consider scale of selection by bobcats when developing habitat management strategies.
文摘Animals that feed from resources that are constant in space and that refill may benefit from repeating the order in which they visit locations.This is a behavior known as traplining,a spatial phenomenon.Hummingbirds,like other central-place foragers,use short traplines when moving between several rewarding sites.Here we investigated whether traplining hummingbirds also use relevant temporal information when choosing which flowers to visit.Wild rufous hummingbirds that were allowed to visit 3 artificial flower patches in which flowers were refilled 20 min after they had been depleted repeated the order in which they visited the 3 patches.Although they tended to visit the first 2 patches sooner than 20 min,they visited the third patch at approximately 20-min intervals.The time between visits to the patches increased across the experiment,suggesting that the birds learned to wait longer before visiting a patch.The birds appeared to couple the sequential pattern of a trapline with temporal regularity,to some degree.This suggests that there is a temporal component to the repeated spatial movements flown by foraging wild hummingbirds.
