Linked paper: Nest-site selection and nest success of an Arctic-breeding passerine, Smith’s Longspurs, in a changing climate by H.R. McFarland, S. Kendall, and A.N. Powell, The Condor: Ornithological Applications 119:1, February 2017.
How will songbirds that nest in tundra respond as the Arctic transforms into a warmer and shrubbier environment? This is the question that drove us to study a small songbird known as the Smith’s Longspur. Endemic to North America, this songbird breeds in only a few remote mountain valleys in Canada and Alaska, making it particularly susceptible to changes at northern latitudes. Smith’s Longspur’s are also unique in that they are polygynandrous. This is a rare mating strategy where both sexes are polygamous, and birds of either sex may mate with up to three individuals each breeding season. Rather than a single male and female establishing a territory, Smith’s Longspurs usually form larger groups called neighborhoods which contain many inter-mated individuals. Since this mating strategy is poorly understood and so different from other tundra nesting songbirds, it is difficult to predict how breeding Smith’s Longspurs may respond to climate change. Therefore, prior to further change, baseline information about breeding requirements is needed.
To fill this void, we monitored more than 250 Smith’s Longspur nests between 2007 and 2013 in the Brooks Range of Alaska. All of the nests were found in open tundra areas, and females never placed their nests in tall vegetation. Aside from a lack of tall shrubs, no specific habitat features that we measured influenced where females placed their nests. This finding is contrary to patterns commonly observed in monogamous ground-nesting birds where females tend to nest near a specific habitat feature. We believe that Smith’s Longspurs may deviate from this pattern because of their unique breeding strategy. Females may benefit more by nesting near other females where the chance of “hooking up” with additional males is greater. If this is the case, nest site selection may occur at a larger neighborhood scale. Considering these findings, we are concerned that future shrub growth in the Arctic could limit the amount of open tundra areas available for breeding neighborhoods of Smith’s Longspurs.
Although there may be fewer available nest sites in the future, warmer temperatures could benefit breeding Smith’s Longspurs. In this study, nests survived best when there were more warm days during the nesting period. Cold temperatures appeared to have no impact on nest success, possibly because females were able to delay nesting until weather conditions were favorable. During these years, females usually began nesting within a few days of one another, compared to years with good conditions early in the season when egg laying was spread out over several weeks. Considering that Smith’s Longspurs breed in the Arctic, it is not surprising that they have adapted strategies to withstand harsh conditions. Because of this adaptive ability, as well as the predicted increase in temperature throughout the Arctic, we believe that breeding Smith’s Longspurs could become more productive in the future. Even so, the combined outcome of reduced suitable habitat but potentially higher breeding productivity is still unknown. Continued monitoring of Smith’s Longspurs is needed as northern regions continue to change.