Anseriformes, the fastest-flying birds in our sample, exhibit onl

Anseriformes, the fastest-flying birds in our sample, exhibit only moderate

eye sizes, while the Accipitridae, grouped within the Falconiformes, are the largest-eyed birds measured but have only moderate flight speeds. We, therefore, conclude that Leuckart’s Law as a simple expression of flight speed is not useful for explaining bird eye sizes. “
“In many polygynous mammals, sexual size dimorphism (SSD) is thought to have evolved through sexual selection, because larger males prevail in male–male combat and secure access to estrous females. SSD is often correlated with higher age-specific mortality of males than selleck inhibitor of females, possibly because males have higher nutritional requirements and riskier growth and reproductive tactics. Y-27632 chemical structure In adult chamois Rupicapra rupicapra, sexual dimorphism in skeletal size was about 5%, but dimorphism in body

mass was highly seasonal. Males were about 40% heavier than females in autumn but only 4% heavier in spring. For a given skeletal size, males were heavier than females only in autumn. Chamois sexual dimorphism appears mainly due to greater summer accumulation of fat and muscle mass by males than by females. Male mass declines rapidly during the rut. Limited dimorphism in skeletal size combined with substantial but seasonal dimorphism in mass has not been reported in other sexually dimorphic ungulates. Seasonal changes in mass allow males to achieve large size for the rut by accumulating body resources during summer. The use of these resources over the rut may reduce mortality associated with sustaining

a large size over the winter. “
“Optimal escape theory predicts that animals should moderate their flight responses according to the level of risk represented by a potential predator. This theory should apply even when organisms are habituated see more to disturbance, and how animals respond to human presence is likely to determine their success exploiting urban habitats. Therefore, urban animals should be sensitive to cues that inform them about levels of risk, allowing them to reduce costs by not overreacting to innocuous stimuli, while ensuring that they are nevertheless reactive to genuinely threatening stimuli. We tested this at a highly urbanized site in New York City, where eastern grey squirrels appear to pay little attention to humans. Squirrels were approached tangentially on a trajectory that took the observer within ∼2 m of them and we measured alert distance, flight initiation distance (FID), and distance fled for each focal individual. Squirrels showed little sign of being alerted to the pedestrian if he remained on the footpath and did not look at them (only 5% of individuals moved away), but 90% of squirrels moved away, with longer FID and flight distance, when approached by a pedestrian that moved off the footpaths and looked at them. Squirrels therefore modulate their reactions when pedestrians behave in a predictable manner (i.e.

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