<P> As its name implies, the barn swallow typically nests inside accessible buildings such as barns and stables, or under bridges and wharves . Before man - made sites became common, it nested on cliff faces or in caves, but this is now rare . The neat cup - shaped nest is placed on a beam or against a suitable vertical projection . It is constructed by both sexes, although more often by the female, with mud pellets collected in their beaks and lined with grasses, feathers, algae or other soft materials . The nest building ability of the male is also sexually selected; females will lay more eggs and at an earlier date with males who are better at nest construction, with the opposite being true with males that are not . After building the nest, barn swallows may nest colonially where sufficient high - quality nest sites are available, and within a colony, each pair defends a territory around the nest which, for the European subspecies, is 4 to 8 m (43 to 86 sq ft) in size . Colony size tends to be larger in North America . </P> <P> In North America at least, barn swallows frequently engage in a mutualist relationship with ospreys . Barn swallows will build their nest below an osprey nest, receiving protection from other birds of prey that are repelled by the exclusively fish - eating ospreys . The ospreys are alerted to the presence of these predators by the alarm calls of the swallows . </P> <P> There are normally two broods, with the original nest being reused for the second brood and being repaired and reused in subsequent years . The female lays two to seven, but typically four or five, reddish - spotted white eggs . The clutch size is influenced by latitude, with clutch sizes of northern populations being higher on average than southern populations . The eggs are 20 mm × 14 mm (0.79 in × 0.55 in) in size, and weigh 1.9 g (0.067 oz), of which 5% is shell . In Europe, the female does almost all the incubation, but in North America the male may incubate up to 25% of the time . The incubation period is normally 14--19 days, with another 18--23 days before the altricial chicks fledge . The fledged young stay with, and are fed by, the parents for about a week after leaving the nest . Occasionally, first - year birds from the first brood will assist in feeding the second brood . Compared to those from early broods, juvenile barn swallows from late broods have been found to migrate at a younger age, fuel less efficiently during migration and have lower return rates the following year . </P> <P> The barn swallow will mob intruders such as cats or accipiters that venture too close to their nest, often flying very close to the threat . Adult barn swallows have few predators, but some are taken by accipiters, falcons, and owls . Brood parasitism by cowbirds in North America or cuckoos in Eurasia is rare . </P>

What does a barn swallow egg look like
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