Span-ratio Analysis Used to Estimate Effective Lift: Drag Ratio in the Double-crested Cormorant Phalacrocorax Auritus from Field Observations

نویسنده

  • C. J. PENNYCUICK
چکیده

A method is described for measuring the effective lift: drag ratio of a bird in napping flight from the bird's span ratio; that is, the ratio of the wing span in the upstroke to that in the downstroke. The method depends on the assumptions that the circulation on the wing is constant, and that the lift varies in proportion to the span. With some simplifications, it can be applied in the field to birds that cruise in steady, continuous flapping flight. Double-crested cormorants, observed on foraging nights, flew at a mean airspeed of 14-7 m s ~ \ with a span ratio of 0-70. The effective lift: drag ratio, taking account of mechanical components of power only, was estimated to be 14-8. A much lower estimate (8-96) was obtained from a power curve program (Pennycuick, 1989). The discrepancy could be due (at least partly) to bias in the observations, but it is also suggested that one or more of the default values, used in the program for calculating induced, profile and parasite power, may be in need of downward revision.

برای دانلود رایگان متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید

ثبت نام

اگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید

منابع مشابه

Isotopic Discrimination in the Double-Crested Cormorant (Phalacrocorax auritus)

The diet-tissue discrimination factor is the amount by which a consumer's tissue varies isotopically from its diet, and is therefore a key element in models that use stable isotopes to estimate diet composition. In this study we measured discrimination factors in blood (whole blood, red blood cells and plasma), liver, muscle and feathers of Double-crested Cormorants (Phalacrocorax auritus) for ...

متن کامل

Identification of 24 polymorphic microsatellite markers for the double-crested cormorant (Phalacrocorax auritus).

Twenty-four polymorphic microsatellite markers were developed for the double-crested cormorant (Phalacrocorax auritus). The number of alleles ranged from two to 13 and observed heterozygosities ranged from 0.032 to 0.871. The use of these loci should enable researchers and biologists to learn more about the population structure and ecology of this species.

متن کامل

Using species distribution models to define nesting habitat of the eastern metapopulation of double‐crested cormorants

When organisms with similar phenotypes have conflicting management and conservation initiatives, approaches are needed to differentiate among subpopulations or discrete groups. For example, the eastern metapopulation of the double-crested cormorant (Phalacrocorax auritus) has a migratory phenotype that is culled because they are viewed as a threat to commercial and natural resources, whereas re...

متن کامل

Depredation of Catfish by Double-crested Cormorants at Aquaculture Facilities in Oklahoma

Oklahoma has about 324 ha of surface water in catfish (Ictalurus spp.) production. The state also supports a large number of migrating and wintering piscivorous birds, particularly double-crested cormorants (Phalacrocorax auritus). To address concerns of aquaculture facility operators regarding loss of fish to cormorants, we asked 11 operators to conduct regular counts of piscivorous birds at e...

متن کامل

ذخیره در منابع من


  با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید

عنوان ژورنال:

دوره   شماره 

صفحات  -

تاریخ انتشار 2005