Nest-site preference and reproductive performance of Song Sparrows (Melospiza melodia) in historically extant and colonist shrub species

Abstract

Many studies report mixed results on the influence of invasive plants on native animals, partly due to uncertainties about habitat preference and reproductive performance in native animals before and after plant invasion. We used vegetation surveys 20 years apart and 18 years of breeding data from Song Sparrows (Melospiza melodia (A. Wilson, 1810)) to compare nest-site preference and reproductive performance during the colonization of Mandarte Island, British Columbia, by one shrub species native to the region but historically absent from the island (red elderberry, Sambucus racemosa L.) and another species that is exotic to North America (Himalayan blackberry, Rubus armeniacus Focke = Rubus bifrons Vest). Nest-site preference declined where red elderberry increased but was unrelated to change in the cover of Himalayan blackberry. Song Sparrows nested in trailing blackberry (Rubus ursinus Cham. and Schltdl.) and its exotic congener Himalayan blackberry in preference to two common shrubs native to Mandarte Island (Nootka rose, Rosa nutkana C. Presl; snowberry, Symphoricarpos albus (L.) S.F. Blake) and built just 1 of 1051 nests in red elderberry. In contrast, reproductive performance was similar in all shrub species used regularly as nest substrates. Our results show that Song Sparrow nest-site preference and reproductive performance were independent of plant species origin.