BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

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Background In-flight conditions are hypothesized to influence the timing and success of long-distance migration. Wind assistance and thermal uplift are thought to reduce the energetic costs of flight, humidity, air pressure and temperature may affect the migrants’ water balance, and clouds may impede navigation. Recent advances in animal-borne long-distance tracking enable evaluating the importance of these factors in determining animals’ flight altitude. Methods Here we determine the effects of wind, humidity, temperature, cloud cover, and altitude (as proxy for climbing costs and air pressure) on flight altitude selection of two long-distance migratory shorebirds, far eastern curlew (Numenius madagascariensis) and whimbrel (Numenius phaeopus). To reveal the predominant drivers of flight altitude selection during migration we compared the atmospheric conditions at the altitude the birds were found flying with conditions elsewhere in the air column using conditional logistic mixed effect models. Results Our results demonstrate that despite occasional high-altitude migrations (up to 5550 m above ground level), our study species typically forego flying at high altitudes, limiting climbing costs and potentially alleviating water loss and facilitating navigation. While mainly preferring migrating at low altitude, notably in combination with low air temperature, the birds also preferred flying with wind support to likely reduce flight costs. They avoided clouds, perhaps to help navigation or to reduce the risks from adverse weather. Conclusions We conclude that the primary determinant of avian migrant’s flight altitude selection is a preference for low altitude, with wind support as an important secondary factor. Our approach and findings can assist in predicting climate change effects on migration and in mitigating bird strikes with air traffic, wind farms, power lines, and other human-made structures.

No abstract

From August 2013, we undertook a 1-year trial of mitigation techniques at an electricity power line in the Mongolian steppe with a high avian electrocution rate. We examined 2 mitigation methods at phase-1 conductors on the top of power poles (i.e., reconfiguration of the insulator mount and insulation covers on the conductor wire) and 3 mitigation methods at phase-2 and 3 conductors on pole cross-arms (i.e., perch deflector brushes, rotating-mirror perch deterrents, and insulation covers on the conductor wires). The perch management techniques selected for the trial are currently widely adopted by power line managers in Mongolia. In comparison with the control, with no mitigation, electrocution rates were reduced both by the reconfiguration of insulator mounts and insulation of conductor wires at phase-1, though the reduction was greater for the former-73% mean reduction for reconfigured mounts and 59% for insulation covers. Electrocution rates were reduced by the placement of rotating-mirrors and insulation of conductor wires at phases 2 and 3, with the reduction being greater for the former-91% mean reduction for mirrors and 66% for insulation covers. Deployment of metal perch deflector brushes at phases 2 and 3 had no effect on electrocution rates and should not be used as mitigation. Most electrocutions occurred at phase 1 on the top of the pole, indicating that mitigation should be prioritized at this phase. In terms of cost and efficacy, reconfigured mounts represented the best option as a permanent fix at phase 1. At phases on cross-arms, the relative merits of mirrors and insulation covers need to be assessed over a longer period, and these temporary mitigation measures should be compared with alternative permanent fixes.