User:KingdomofAnimalia/Pacific wren

Breeding
The male builds a small number of nests. These are called "cock nests" but are never lined until the female chooses one to use. The normal round nest of grass, moss, lichens or leaves is tucked into a hole in a wall, tree trunk, crack in a rock or corner of a building, but it is often built in bushes, overhanging boughs or the litter which accumulates in branches washed by floods. Five to eight white or slightly speckled eggs are laid in April, and second broods are reared.

A particular facet of the Pacific Wren is that the males use intricate vocalizations to attract females for mating. Pacific Wrens are songbirds and the songs are used for mating purposes as well as for territorial displays. In British Columbia, Canada, male Pacific Wren have been observed to adapt their songs in the presence of highway noise. Pacific Wrens are widely known for their variety and complexity of song. In adaptation to the noise of freeway traffic, male Pacific wrens were observed to change the overall length of their songs. However, other changes in song variation and individual syllable length could not be concluded.

A variation in reproduction success has been observed at higher altitudes. In the forests of British Columbia, at higher altitudes, in 2003-2004 there was a decline in breeding compared with lower altitudes of habitation for the Pacific Wren. Specifically, the length of breeding season was shorter and the survival rates of nests were lower. However, other factors such as incubation length and the total number of eggs in each nesting attempt showed no variation due to elevation. Although the Pacific Wren overall lacked adaptation to higher altitudes, there was a small percentage of Pacific Wrens that were able to successfully reproduce at these higher elevations.

Adaptations in breeding patterns within urban landscapes were observed in the Seattle, Washington area and its surrounding forests. In the developing urban ecosystems of the city, Pacific Wren fled and relocated to nearby forests. Due to this change of location, breeding success for those Pacific Wren declined significantly. The proportion of wrens returning to the same urban nest in the greater Seattle, Washington area was in some cases observed to be as low as 0%. In this case, the Pacific Wren’s relocation in conjunction with its inability to cultivate a successful new nesting site is what contributed to the decline in reproduction.

In contrast, a close relative of the Pacific Wren, the Bewick’s wren has been highly successful at thriving in certain urban environments. This stands in polarity to the Pacific Wren's diminished numbers in urban areas. Moreover, the Bewick’s Wren, otherwise known as Thryomanes bewickii, has been observed to interact aggressively with the Pacific Wren. However, the exact reasons for Bewick Wren’s success vs. Pacific Wren’s diminishing numbers in urban areas are unclear. Overall, observations are in favor of the hypothesis that urban landscapes foster aggressive and combative interactions between native species.