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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 groundspeeds 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 groundspeed, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Scatter plot and regression line with 95 % confidence interval illustrating relationship between groundspeed and tailwind component. Squares and circles represent adult and juvenile birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained from the partial regression where the effect of route has been removed from both groundspeed and tailwind component
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Fig5: a Box plot illustrating differences in groundspeeds 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 groundspeed, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Scatter plot and regression line with 95 % confidence interval illustrating relationship between groundspeed and tailwind component. Squares and circles represent adult and juvenile birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained from the partial regression where the effect of route has been removed from both groundspeed and tailwind component

Mentions: Similar to flight duration, we found that both age and flight stage influenced groundspeed, and that these effects were indirectly mediated by the tailwind components experienced aloft (Fig. 3b and Table 2). In fact, given the model structure, the effects of age and flight stage on the tailwind component experienced during flight are identical to those reported for the flight duration model above (Tables 1 and 2). The net effect of these indirect relationships was that adults flew 3 m/s and 5 m/s faster on average than juveniles over the ocean and down the coast, respectively (median groundspeed: juvenile ocean = 7 m/s (4–11 m/s); adult ocean = 10 m/s (5–16 m/s); juvenile coast = 13 m/s (7–28 m/s); adult coast = 18 m/s (11–40 m/s); Fig. 5a). Specifically, and again similar to our model involving flight duration, juveniles tended to depart and fly with less supportive tailwind components relative to adults which had the effect of decreasing their groundspeeds relative to adults (intercept = 0.51; βtailwind = 0.58; Fig. 5b and Table 2). Different from our flight duration model, we also found a direct effect of flight stage on log groundspeed, where after controlling for the effect of tailwind component experienced aloft, groundspeed was much faster along the coast than over the ocean (βroute:ocean = −0.87; Fig. 5a and Table 2). The net effect of the direct and indirect effects of flight stage on groundspeed was that birds were flying 7 m/s faster, on average, down the coast as opposed to over the ocean (median groundspeed: ocean = 10 m/s (4–17 m/s); coast = 17 m/s (7–40 m/s); Fig. 5a).Table 2


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 groundspeeds 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 groundspeed, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Scatter plot and regression line with 95 % confidence interval illustrating relationship between groundspeed and tailwind component. Squares and circles represent adult and juvenile birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained from the partial regression where the effect of route has been removed from both groundspeed and tailwind component
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig5: a Box plot illustrating differences in groundspeeds 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 groundspeed, respectively. Hollow circles represent values lying outside 1.5 * the interquartile range. b Scatter plot and regression line with 95 % confidence interval illustrating relationship between groundspeed and tailwind component. Squares and circles represent adult and juvenile birds, respectively, while grey and black points represent ocean and coastal routes, respectively. R2 represents the marginal deviance explained from the partial regression where the effect of route has been removed from both groundspeed and tailwind component
Mentions: Similar to flight duration, we found that both age and flight stage influenced groundspeed, and that these effects were indirectly mediated by the tailwind components experienced aloft (Fig. 3b and Table 2). In fact, given the model structure, the effects of age and flight stage on the tailwind component experienced during flight are identical to those reported for the flight duration model above (Tables 1 and 2). The net effect of these indirect relationships was that adults flew 3 m/s and 5 m/s faster on average than juveniles over the ocean and down the coast, respectively (median groundspeed: juvenile ocean = 7 m/s (4–11 m/s); adult ocean = 10 m/s (5–16 m/s); juvenile coast = 13 m/s (7–28 m/s); adult coast = 18 m/s (11–40 m/s); Fig. 5a). Specifically, and again similar to our model involving flight duration, juveniles tended to depart and fly with less supportive tailwind components relative to adults which had the effect of decreasing their groundspeeds relative to adults (intercept = 0.51; βtailwind = 0.58; Fig. 5b and Table 2). Different from our flight duration model, we also found a direct effect of flight stage on log groundspeed, where after controlling for the effect of tailwind component experienced aloft, groundspeed was much faster along the coast than over the ocean (βroute:ocean = −0.87; Fig. 5a and Table 2). The net effect of the direct and indirect effects of flight stage on groundspeed was that birds were flying 7 m/s faster, on average, down the coast as opposed to over the ocean (median groundspeed: ocean = 10 m/s (4–17 m/s); coast = 17 m/s (7–40 m/s); Fig. 5a).Table 2

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