Dunnock relatively lower success for females. In times of scarcity, female territories expand to accommodate the lack of resources, causing males to have a more difficult time monopolizing females. Hence, females gain a reproductive advantage over males in this case. The dunnock possesses variable mating systems. Females are often polyandrous, breeding with two or more males at once, which is quite rare among birds. This multiple mating system leads to the development of sperm competition amongst the male suitors. DNA fingerprinting has shown that chicks within a brood often have different fathers, depending on the success of the males at monopolising
Common ostrich is scarce in dry and hot environment, and this poses a challenge to the ostrich's water consumption. Also the ostrich is a ground bird and cannot fly to find water sources, which poses a further challenge. Because of their size, common ostriches cannot easily escape the heat of their environment; however, they dehydrate less than their small bird counterparts because of their small surface area to volume ratio. Hot, arid habitats pose osmotic stress, such as dehydration, which triggers the common ostrich’s homeostatic response to osmoregulate. The common ostrich is well adapted to hot, arid environments through specialization of excretory