About swallow nest, swiftlet, edible bird’s nest

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

biologists.org
Kirsty J. Park1,*, Mikael Rosén2 and Anders Hedenström2

1 Department of Biological Sciences, University of Stirling, Stirling FK9 4LA, UK and
2 Department of Animal Ecology, Lund University, SE-223 62 Lund, Sweden

*Author for correspondence (e-mail: k.j.park@stir.ac.uk)

Accepted May 14, 2001

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 4–14ms-1. Wingbeat frequency showed a clear U-shaped relationship with air speed with minima at 8.9ms-1(bird 1) and 8.7ms-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, which is 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 wingbeat kinematics and use of the tail that birds have available to them in order to adjust the lift and power output required for flight.

Key words: flight, kinematics, wind tunnel, flap-gliding, barn swallow, Hirundo rustica.

Add comment October 13th, 2006

Evolution of Nest Construction in Swallows (Hirundinidae): A Molecular Phylogenetic Perspective

pnas.or
DW Winkler and FH Sheldon

Nest construction is more diverse in the Hirundinidae than in any other family of oscine birds. To explore the evolution of this diversity, we superimposed nest data on a DNA-hybridization phylogeny of 17 swallow species. Nest construction is tightly linked to the inferred evolutionary history. Burrowing appears to be the primitive nesting mode, and burrowing ancestors gave rise to cavity-adopting and mud-nesting clades. Obligate cavity adoption is mostly confined to a monophyletic clade in the New World, and the diversification of obligate nest adopters appears to be tied to the richness of forest habitats and recent active mountain building there. Construction of mud nests originated only once in the history of the group, and mud-nesters have diversified principally in Africa, where a drier climatic history has favored their mode of nesting. The use of pure mud to construct a hanging nest is unique among all birds, and we infer that mud nests have increased in complexity during evolution from simple mud cups to fully enclosed retort-shaped nests. This increased complexity appears to have been the critical precursor for the evolution of high-density colonial mud-nesters.

Add comment October 13th, 2006