Flight kinematics of the barn swallow (Hirundo rustica) over a wide range of speeds in a windtunnel

Two barn swallows (Hirundo rustica) flying in the Lund wind tunnel were filmed using synchronised high-speed cameras to obtain posterior, ventral and lateral views of the birds in horizontal flapping flight. We investigated wingbeat kinematics, body tilt angle, tail spread and angle of attack at speeds of 4 to 14 ms-1. Wingbeat frequency showed a clear U-shaped relationship with air speed with minima at 8.9 ms-1 (bird #1) and 8.7 ms-1 (bird #2). A method previously used by other authors of estimating the body drag coefficient (CD,par) by obtaining agreement between the calculated minimum power (Vmin) and the observed minimum wingbeat frequency does not appear to be valid in this species, possibly due to upstroke pauses that occur at intermediate and high speeds, causing the apparent wingbeat frequency to be lower. These upstroke pauses represent flap-gliding, possibly a way of adjusting the force generated to the requirements at medium and high speeds, similar to the flap-bound mode of flight in other species. Body tilt angle, tail spread and angle of attack all increase with decreasing speed, thereby providing an additional lift surface and suggesting an important aerodynamic function for the tail at low speeds in forward flight. Results from this study indicate the high plasticity in the wing beat kinematics and use of the tail that birds have available to them in order to adjust the lift and power output required for flight

Climb and flight speeds of shorebirds embarking on an intercontinental flight:Do they achieve the predicted optimal behaviour?

Most Arctic-breeding waders wintering in West Africa cover the first 4000 km of their northward journey in spring by a single flight to western Europe. We examined the extent to which waders economize their night behaviour during departure by comparing climb rates and forward night speeds with predictions based on flight mechanic theory and the relevant morphological measurements made of birds collected on the site. With an optical range finder, we followed 98 wader necks on their departure from Banc d'Arguin in Mauritania, We also measured wind speed and direction at different altitudes by tracking helium-filled balloons and thus were able to deduce airspeeds from groundspeeds of the departing flocks. Of the nine species examined, six showed the predicted negative relationship between climb rate and airspeed, although only one was statistically significant. By normalizing the data, we found a statistically significant negative correlation across all species. Although 17% of the observed climb rates were greater than the predicted theoretical maximum, the average observed climb rate was lower than the predicted optimum and the average observed airspeed was higher. The absolute deviations of climb rates fr om theory may have been because of the existence of pockets of rising and sinking air at the boundary of desert and ocean. That the absolute deviations in average climb rate and airspeed followed the predicted negative relationship is in accordance with the current theory of flight mechanics

Challenging claims in the study of migratory birds and climate change

Recent shifts in phenology in response to climate change are well established but often poorly understood. Many animals integrate climate change across a spatially and temporally dispersed annual life cycle, and effects are modulated by ecological interactions, evolutionary change and endogenous control mechanisms. Here we assess and discuss key statements emerging from the rapidly developing study of changing spring phenology in migratory birds. These well-studied organisms have been instrumental for understanding climate-change effects, but research is developing rapidly and there is a need to attack the big issues rather than risking affirmative science. Although we agree poorly on the support for most claims, agreement regarding the knowledge basis enables consensus regarding broad patterns and likely causes. Empirical data needed for disentangling mechanisms are still scarce, and consequences at a population level and on community composition remain unclear. With increasing knowledge, the overall support (‘consensus view’) for a claim increased and between-researcher variability in support (‘expert opinions') decreased, indicating the importance of assessing and communicating the knowledge basis. A proper integration across biological disciplines seems essential for the field's transition from affirming patterns to understanding mechanisms and making robust predictions regarding future consequences of shifting phenologies

Allometry of the Duration of Flight Feather Molt in Birds

Replacement of flight feathers takes disproportionately more time for large birds than it does for small birds, because feather length increases with body size almost twice as fast as feather growth rate increases

Intraspecific variation in avian pectoral muscle mass: constraints on maintaining manoeuvrability with increasing body mass

1. Within a single year, long-distance migrants undergo a minimum of four cycles of fuel storage and depletion because their migrations have at least one stopover. Each cycle includes an almost twofold change in body mass (mb). Pervasive predation threats beg the question whether escape flight abilities keep up with such large changes in mb. 2. We derive aerodynamic predictions how pectoral muscle mass (mpm) should change with mb to maintain constant relative flight power. 3. We tested these predictions with data on red knot Calidris canutus, a long-distance migrating wader that breeds in arctic tundra and winters in temperate and tropical coastal areas. We focused on the subspecies C. c. islandica. 4. mpm varied with mb in a piecewise manner. In islandica knots with mb ≤ 148 g, the slope (1·06) was indistinguishable from the prediction (1·25). In heavy knots (mb > 148 g) the slope was significantly lower (0·63), yielding a mpm 0·81 times lower than predicted at pre-departure weights (210 g). 5. Manoeuvrability tests showed that above 160 g, knots were increasingly unable to make a 90° angle turn. This is consistent with mpm being increasingly smaller than predicted. 6. Relatively low mpm enables savings on mass and hence flight costs, and savings on overall energy expenditure. We predict that reduced escape flight ability at high mb will be compensated by behavioural strategies to minimize predation risk.

All laydate

File All laydate: Year = year Sp = Species 1 = Marsh tit; 2 = Blue tit; 3 = Great tit; 4 = Pied flycatcher Reg. = Region 1 = Revinge; 2 = Linnebjer; 3 = Vomb; 4 = Dalby Norreskog; 5 = Frueräften; 6 = Kungsmarken Temp = Mean ambient temperature for the 30 d preceding the mean laying date for each species and year Date = Laying of the first egg in a clutch; 1 = 1 April Anno = Year since the first year in the study; 1 = 196

Challenging claims in the study of migratory birds and climate change

Recent shifts in phenology in response to climate change are well established but often poorly understood. Many animals integrate climate change across a spatially and temporally dispersed annual life cycle, and effects are modulated by ecological interactions, evolutionary change and endogenous control mechanisms. Here we assess and discuss key statements emerging from the rapidly developing study of changing spring phenology in migratory birds. These well-studied organisms have been instrumental for understanding climate-change effects, but research is developing rapidly and there is a need to attack the big issues rather than risking affirmative science. Although we agree poorly on the support for most claims, agreement regarding the knowledge basis enables consensus regarding broad patterns and likely causes. Empirical data needed for disentangling mechanisms are still scarce, and consequences at a population level and on community composition remain unclear. With increasing knowledge, the overall support ('consensus view') for a claim increased and between-researcher variability in support ('expert opinions') decreased, indicating the importance of assessing and communicating the knowledge basis. A proper integration across biological disciplines seems essential for the field's transition from affirming patterns to understanding mechanisms and making robust predictions regarding future consequences of shifting phenologies.</p

Evolution of chain migration in an aerial insectivorous bird, the common swift Apus apus

Spectacular long-distance migration has evolved repeatedly in animals enabling exploration of resources separated in time and space. In birds, these patterns are largely driven by seasonality, cost of migration, and asymmetries in competition leading most often to leap-frog migration, where northern breeding populations winter furthest to the south. Here we show that the highly aerial common swift Apus apus, spending the non-breeding period on the wing, instead exhibits a rarely-found chain migration pattern, where the most southern breeding populations in Europe migrate to wintering areas furthest to the south in Africa, while the northern populations winter to the north. The swifts concentrated in three major areas in sub-Saharan Africa during the non-breeding period, with substantial overlap for nearby breeding populations. We found that the southern breeding swifts were larger, raised more young, and arrived to the wintering areas with higher seasonal variation in greenness (Normalized Difference Vegetation Index, NDVI) earlier than the northern breeding swifts. This unusual chain migration pattern in common swifts is largely driven by differential annual timing and we suggest it evolves by prior occupancy and dominance by size in the breeding quarters and by prior occupancy combined with diffuse competition in the winter.,Average winter position in November and December fo rindividually tracked common swifts (Apus apus) breeding in Europe. Tracking method geolocation by light. Clutch size measured as maximum number of young in nest. Wing and mass of common swifts breeding in Europe. Wing and mass collected during ringing at breeding sites.