Devin de Zwaan
University of British Columbia https://www.researchgate.net/profile/Devin_De_Zwaan
Interested in birds and conservation and want to help? We are looking for sightings of colour banded Horned Larks during Autumn & Spring migration, as well as the winter. You too can help track the movement of alpine Horned Larks by birding in strategic locations and submitting your sightings. See here for details.
Alpine breeding songbirds are fascinating, often operating at their energy limits to successfully balance survival and reproduction (Photo #1). With snow cover often extending well into June and frequent snowstorms producing harsh, uncertain conditions, the alpine breeding season is short, usually only lasting about 30–45 days. As a result, alpine songbirds spend ≥ 75% of the annual cycle in low elevation habitats. Despite advances in tracking technology over the last decade, the non-breeding behaviour and habitats of alpine birds are still relatively unknown, largely because of the research challenges associated with accessing alpine populations. The ways in which birds use the landscape can significantly influence individual fitness and thus population dynamics. Therefore, movements of alpine breeding birds and the degree to which they mix with low elevation populations is vital information for understanding the threats to alpine populations.
The goal of my research was to begin addressing some of these unknowns using alpine Horned Larks (Eremophila alprestris) that breed in northern British Columbia, near the town of Smithers. We first identified where alpine larks go during the winter and how long they use specific non-breeding habitats. To do this, we used light-level geolocators to track the migration of an alpine population of Horned Larks from 2015 to 2017. Geolocators are attached to the birds like small backpacks (Photo #2), and they recorded day length and the timing of peak sun elevation. With these data and some serious modeling, we can narrow down the daily location of a bird to an accuracy of about ± 40 km.
Where did they go?
Larks from this alpine population are short-distance migrants. They predominantly travelled south down the Coastal Mountain range to the Okanagan Valley, before travelling further south to settle east of the Cascades in Washington, Oregon and Idaho. We outlined several intriguing cases of sex differences and flexibility in migratory behaviour in the linked paper. However, a stand-out result with particular importance for conservation organizations like Partners in Flight was the exceptionally prolonged use of certain spring stopover sites. Approximately 60% of tracked individuals stopped over in the northern Columbia Plateau and Okanagan highlands for an average of 41 days at a time (range: 21 to 66 days). Additionally, birds that stopped over were more likely to successfully fledge offspring than those who migrated straight from their wintering site farther south.
What does this mean?
Increasingly, we are understanding that how birds move through and use the landscape during the non-breeding season can carry-over to affect individual fitness and reproductive success. This is particularly topical because the loss or degradation of important non-breeding habitats due to land-use or climate change can have severe impacts on population growth. The extended stopover behaviour we observed suggests that the northern Columbia Plateau and South Okanagan may be critical non-breeding habitat, not only for this alpine population, but potentially several other alpine and even arctic lark populations. A quick look at eBird sightings of Horned Lark in March over the past two decades reveals sightings of hundreds or even thousands of larks in these regions.
Continued development and degradation of native short-grass habitat is thus a concern. This highlights the importance of not only protecting critical grassland habitat, but also working with private landowners through stewardship programs to find mutually beneficial solutions for both agriculture and conservation.
The Breeding Bird Survey (BBS) indicates that Horned Larks have declined by 70% since 1970. However, both the BBS and other data sources such as eBird rarely sample alpine or arctic populations. This could mean that we are either under- or over-estimating the future of this species in North America. Research like this project, to identify critical non-breeding habitat and potential future threats, can arm us with the information needed to act now and protect northern alpine migratory birds in the future.
de Zwaan, D. R., Wilson, S., Gow, E. A., & Martin, K. (2019). Sex-specific spatiotemporal variation and carry-over effects in a migratory alpine songbird. Frontiers Eco Evol, 7: 1-12. doi: 10.3389/fevo.2019.00285