Impact on birds

The domestic cat is probably a significant predator of birds. UK assessments indicate that they may be accountable for an estimated 64.8 million bird deaths each year.[129] Certain species appear more susceptible than others; for example, 30% of house sparrow mortality is linked to the domestic cat.[174] In the recovery of ringed robins (Erithacus rubecula) and dunnocks (Prunella modularis), it was also concluded that 31% of deaths were a result of cat predation.[175] The presence of larger carnivores such as coyotes which prey on cats and other small predators reduces the effect of predation by cats and other small predators such as opossums and raccoons on bird numbers and variety.[176] The proposal that cat populations will increase when the numbers of these top predators decline is called the mesopredator release hypothesis. On islands, birds can contribute as much as 60% of a cat's diet.[177] In nearly all cases, however, the cat cannot be identified as the sole cause for reducing the numbers of island birds, and in some instances eradication of cats has caused a mesopredator release effect;[178] where the suppression of top carnivores creates an abundance of smaller predators that cause a severe decline in their shared prey. Domestic cats are, however, known to be a contributing factor to the decline of many species; a factor that has ultimately led, in some cases, to extinction. The South Island Piopio, Chatham Islands Rail,[175] the Auckland Islands Merganser,[179] and the common diving petrel[180] are a few from a long list, with the most extreme case being the flightless Stephens Island Wren, which was driven to extinction only a few years after its discovery.[181][182] Some of the same factors that have promoted adaptive radiation of island avifauna over evolutionary time appear to promote vulnerability to non-native species in modern time. The susceptibility inherent of many island birds is undoubtedly due to evolution in the absence of mainland predators, competitors, diseases and parasites. In addition to lower reprod ctive rates and extended incubation periods.[183] The loss of flight, or reduced flying ability is also characteristic of many island endemics.[184] These biological aspects have increased vulnerability to extinction in the presence of introduced species, such as the domestic cat.[185] Equally, behavioural traits exhibited by island species, such as "predatory naivety"[186] and ground-nesting,[183] have also contributed to their susceptibility. The House Sparrow (Passer domesticus) is a bird of the sparrow family Passeridae, found in most parts of the world. A small bird, it has a typical length of 16 cm (6.3 in) and a weight of 2439.5 g (0.851.39 oz). Females and young birds are coloured pale brown and grey, and males have brighter black, white, and brown markings. One of about 25 species in the genus Passer, the House Sparrow occurs naturally in most of Europe, the Mediterranean region, and much of Asia. Its intentional or accidental introductions to many regions, including parts of Australia, Africa, and the Americas, make it the most widely distributed wild bird. The House Sparrow is strongly associated with human habitations, and can live in urban or rural settings. Though found in widely varied habitats and climates, it typically avoids extensive woodlands, grasslands, and deserts away from human development. It feeds mostly on the seeds of grains and weeds, but it is an opportunistic eater and commonly eats insects and many other foods. Its predators include domestic cats, hawks, owls, and many other predatory birds and mammals. Because of its numbers, ubiquity and association with human settlements, the sparrow is culturally prominent. It is extensively, and usually unsuccessfully, persecuted as an agricultural pest, but it has also often been kept as a pet as well as being a food item and a symbol of lust and sexual potency, as well as of commonness and vulgarity. Though it is widespread and abundant, its numbers have declined in some areas. The animal's conservation status is listed as Least Concern on the IUCN Red List.