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Automated telemetry reveals age specific differences in flight duration and speed are driven by wind conditions in a migratory songbird.

Mitchell GW, Woodworth BK, Taylor PD, Norris DR - Mov Ecol (2015)

Bottom Line: We found that juveniles departed under wind conditions that were less supportive relative to adults and that this resulted in juveniles taking 1.4 times longer to complete the same flight trajectories as adults.We also found that groundspeeds were 1.7 times faster along the coast than over the ocean given more favourable tailwinds along the coast and because birds appeared to be climbing in altitude over the ocean, diverting some energy from horizontal to vertical movement.Our results provide the first evidence that adult songbirds have considerably more efficient migratory flights than juveniles, and that this efficiency is driven by the selection of more supportive tailwind conditions aloft.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1 Canada ; Wildlife Research Division, National Wildlife Research Center, Environment Canada, Ottawa, ON K1H 0H3 Canada.

ABSTRACT

Background: Given that winds encountered on migration could theoretically double or half the energy expenditure of aerial migrants, there should be strong selection on behaviour in relation to wind conditions aloft. However, evidence suggests that juvenile songbirds are less choosy about wind conditions at departure relative to adults, potentially increasing energy expenditure during flight. To date, there has yet to be a direct comparison of flight efficiency between free-living adult and juvenile songbirds during migration in relation to wind conditions aloft, likely because of the challenges of following known aged individual songbirds during flight. We used an automated digital telemetry array to compare the flight efficiency of adult and juvenile Savannah sparrows (Passerculus sandwichensis) as they flew nearly 100 km during two successive stages of their fall migration; a departure flight from their breeding grounds out over the ocean and then a migratory flight along a coast. Using a multilevel path modelling framework, we evaluated the effects of age, flight stage, tailwind component, and crosswind component on flight duration and groundspeed.

Results: We found that juveniles departed under wind conditions that were less supportive relative to adults and that this resulted in juveniles taking 1.4 times longer to complete the same flight trajectories as adults. We did not find an effect of age on flight duration or groundspeed after controlling for wind conditions aloft, suggesting that both age groups were flying at similar airspeeds. We also found that groundspeeds were 1.7 times faster along the coast than over the ocean given more favourable tailwinds along the coast and because birds appeared to be climbing in altitude over the ocean, diverting some energy from horizontal to vertical movement.

Conclusions: Our results provide the first evidence that adult songbirds have considerably more efficient migratory flights than juveniles, and that this efficiency is driven by the selection of more supportive tailwind conditions aloft. We suggest that the tendency for juveniles to be less choosy about wind conditions at departure relative to adults could be adaptive if the benefits of having a more flexible departure schedule exceed the time and energy savings realized during flight with more supportive winds.

No MeSH data available.


Related in: MedlinePlus

a Box plot illustrating differences in flight durations between adults and juveniles for flights over the ocean and along the coast. The hollow squares and horizontal lines within each box represent the mean and median of the variable of interest, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Box plot illustrating difference in tailwind components experienced by juvenile and adult birds pooled across routes. c Scatter plot with curvilinear regression line and 95 % confidence interval illustrating relationship between flight duration and tailwind component. Squares and circles represent juvenile and adult birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained. d Box plot illustrating difference in tailwind components experienced by birds over the ocean and along the coast
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Fig4: a Box plot illustrating differences in flight durations between adults and juveniles for flights over the ocean and along the coast. The hollow squares and horizontal lines within each box represent the mean and median of the variable of interest, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Box plot illustrating difference in tailwind components experienced by juvenile and adult birds pooled across routes. c Scatter plot with curvilinear regression line and 95 % confidence interval illustrating relationship between flight duration and tailwind component. Squares and circles represent juvenile and adult birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained. d Box plot illustrating difference in tailwind components experienced by birds over the ocean and along the coast

Mentions: We found that both age and flight stage influenced flight duration, but that these effects were indirectly mediated by the tailwind components experienced aloft (Fig. 3a and Table 1). The net effect of this indirect relationship was that juveniles, on average, took 25 min longer to fly between Kent Is. and the coast and 23 min longer to move down the coast relative to adults (median flight duration: juveniles ocean = 90 min (53–113 min); adults ocean = 58 min (35–113 min); juveniles coast = 80 min (39–128 min); adults coast = 56 min (26–94 min); Fig. 4a). Specifically, we found that juveniles tended to depart with less supportive tailwind components relative to adults (intercept = −0.13; βage:adult = 0.80; Fig. 4b and Table 1), which strongly increased their flight durations (intercept = −0.23; βtailwind = −0.69; βtailwind2 = 0.23; Fig. 4c and Table 1). We also found that birds flying over the ocean tended to experience less supportive tailwind components than along the coast (βstage:ocean = −0.70; Fig. 4d and Table 1). To examine if the flight stage effect was confounded by the use of winds from two different altitudes, we refit the model examining the effects of flight stage on the tail and crosswind components using only winds from either 1000 mbar or 925 mbar. In each model, the flight stage effect was still present and effect sizes were similar (Additional file 1: Table S3).Fig. 3


Automated telemetry reveals age specific differences in flight duration and speed are driven by wind conditions in a migratory songbird.

Mitchell GW, Woodworth BK, Taylor PD, Norris DR - Mov Ecol (2015)

a Box plot illustrating differences in flight durations between adults and juveniles for flights over the ocean and along the coast. The hollow squares and horizontal lines within each box represent the mean and median of the variable of interest, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Box plot illustrating difference in tailwind components experienced by juvenile and adult birds pooled across routes. c Scatter plot with curvilinear regression line and 95 % confidence interval illustrating relationship between flight duration and tailwind component. Squares and circles represent juvenile and adult birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained. d Box plot illustrating difference in tailwind components experienced by birds over the ocean and along the coast
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4537592&req=5

Fig4: a Box plot illustrating differences in flight durations between adults and juveniles for flights over the ocean and along the coast. The hollow squares and horizontal lines within each box represent the mean and median of the variable of interest, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Box plot illustrating difference in tailwind components experienced by juvenile and adult birds pooled across routes. c Scatter plot with curvilinear regression line and 95 % confidence interval illustrating relationship between flight duration and tailwind component. Squares and circles represent juvenile and adult birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained. d Box plot illustrating difference in tailwind components experienced by birds over the ocean and along the coast
Mentions: We found that both age and flight stage influenced flight duration, but that these effects were indirectly mediated by the tailwind components experienced aloft (Fig. 3a and Table 1). The net effect of this indirect relationship was that juveniles, on average, took 25 min longer to fly between Kent Is. and the coast and 23 min longer to move down the coast relative to adults (median flight duration: juveniles ocean = 90 min (53–113 min); adults ocean = 58 min (35–113 min); juveniles coast = 80 min (39–128 min); adults coast = 56 min (26–94 min); Fig. 4a). Specifically, we found that juveniles tended to depart with less supportive tailwind components relative to adults (intercept = −0.13; βage:adult = 0.80; Fig. 4b and Table 1), which strongly increased their flight durations (intercept = −0.23; βtailwind = −0.69; βtailwind2 = 0.23; Fig. 4c and Table 1). We also found that birds flying over the ocean tended to experience less supportive tailwind components than along the coast (βstage:ocean = −0.70; Fig. 4d and Table 1). To examine if the flight stage effect was confounded by the use of winds from two different altitudes, we refit the model examining the effects of flight stage on the tail and crosswind components using only winds from either 1000 mbar or 925 mbar. In each model, the flight stage effect was still present and effect sizes were similar (Additional file 1: Table S3).Fig. 3

Bottom Line: We found that juveniles departed under wind conditions that were less supportive relative to adults and that this resulted in juveniles taking 1.4 times longer to complete the same flight trajectories as adults.We also found that groundspeeds were 1.7 times faster along the coast than over the ocean given more favourable tailwinds along the coast and because birds appeared to be climbing in altitude over the ocean, diverting some energy from horizontal to vertical movement.Our results provide the first evidence that adult songbirds have considerably more efficient migratory flights than juveniles, and that this efficiency is driven by the selection of more supportive tailwind conditions aloft.

View Article: PubMed Central - PubMed

Affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1 Canada ; Wildlife Research Division, National Wildlife Research Center, Environment Canada, Ottawa, ON K1H 0H3 Canada.

ABSTRACT

Background: Given that winds encountered on migration could theoretically double or half the energy expenditure of aerial migrants, there should be strong selection on behaviour in relation to wind conditions aloft. However, evidence suggests that juvenile songbirds are less choosy about wind conditions at departure relative to adults, potentially increasing energy expenditure during flight. To date, there has yet to be a direct comparison of flight efficiency between free-living adult and juvenile songbirds during migration in relation to wind conditions aloft, likely because of the challenges of following known aged individual songbirds during flight. We used an automated digital telemetry array to compare the flight efficiency of adult and juvenile Savannah sparrows (Passerculus sandwichensis) as they flew nearly 100 km during two successive stages of their fall migration; a departure flight from their breeding grounds out over the ocean and then a migratory flight along a coast. Using a multilevel path modelling framework, we evaluated the effects of age, flight stage, tailwind component, and crosswind component on flight duration and groundspeed.

Results: We found that juveniles departed under wind conditions that were less supportive relative to adults and that this resulted in juveniles taking 1.4 times longer to complete the same flight trajectories as adults. We did not find an effect of age on flight duration or groundspeed after controlling for wind conditions aloft, suggesting that both age groups were flying at similar airspeeds. We also found that groundspeeds were 1.7 times faster along the coast than over the ocean given more favourable tailwinds along the coast and because birds appeared to be climbing in altitude over the ocean, diverting some energy from horizontal to vertical movement.

Conclusions: Our results provide the first evidence that adult songbirds have considerably more efficient migratory flights than juveniles, and that this efficiency is driven by the selection of more supportive tailwind conditions aloft. We suggest that the tendency for juveniles to be less choosy about wind conditions at departure relative to adults could be adaptive if the benefits of having a more flexible departure schedule exceed the time and energy savings realized during flight with more supportive winds.

No MeSH data available.


Related in: MedlinePlus