Sentence examples for birds is difficult from inspiring English sources

But tracking the enigmatic and wide-ranging birds is difficult at best.

Aerodynamic theory provides ecologists with a useful tool for understanding the basic physics of flight, but analysing flapping flight aerodynamics in birds is difficult, with interesting physiological complications.

However, an accurate assessment of the number of birds is difficult, since those on the surface of the colony and in the nearby sea form only a small proportion of the variable and poorly understood population.

However, all species of birds exhibit different proportionalities of features, and thus creating a universal surface area equation for birds is difficult.

No systematic investigation has been made of changes in handling procedures, and identifying any specific modification that might have led to major reductions in exposure to infected birds is difficult.

In practice, AIV surveillance of live wild birds is difficult and involves substantial labor and costs, particularly for purchase and maintenance of trapping equipment, salary of trapping staff, and laboratory analysis.

Because grassland birds are difficult to detect when not singing we employed a rope drag technique in which a 25m-long rope connecting two observers was dragged across vegetation to flush birds, increasing their visual detectability and the likelihood of birds to produce species-specific vocalizations that could be used in identification.

*S1, aviary section in which cumulative mortality rate could not be estimated because exact bird population was not known and birds were difficult to observe; S2, aviary section in which captive bird population was exactly known and number of dead birds was precisely recorded; NP, species not present in S1 or S2.

For S1, the cumulative mortality rate could not be estimated because the exact bird population was not known and the birds were difficult to observe in that section (the semicaptive waterfowl population is able to mix with the wild population and disperse to breed).

Vermeule contends that the appearance of the bird is "difficult to describe" but that it has "a healthy individuality and an almost-rustic charm".

Even a singing male may be hard to locate; the perched bird is difficult to spot in low light conditions, and the song has a ventriloquial quality as the singer turns his head.