Alyssa Rosemartin
Coastal development is increasing on a global scale. By 2025, 75% of the world's population will live within 120 miles of the coast (UNESCO). The coast of the northern Gulf of California, one of the richest marine ecosystems in the world, is no exception. The community of Puerto Peñasco, Sonora has grown 7% each year since 2000. Just north of the border, Arizona is the second fastest growing state in the United States, and the fast growing city of Tucson, at 2% each year, seems slow in comparison.
Development on the California coast led to the near decimation of the least tern, a colonial-nesting and endangered seabird. Intensive management and monitoring reversed the trend, leading to the recovery of the species from 225 pairs in 1970 to over 6,000 pairs today. These efforts are lauded as one of the few clear success stories of the Endangered Species Act. We have the opportunity to learn from California's experience, and manage coastal species effectively from the outset. Would a similar recovery story for the least tern even be possible in Mexico?
Pristine beaches and peninsulas are a developer's first target. In the northern gulf, they are home to the least tern, which nests exclusively on flat, undisturbed beaches and spits. The most basic question for management and conservation of this species is, where in this region are their colonies located? In 2007, working with CEDO, a conservation non-profit, I surveyed 100 miles of coastline, locating 7 colonies and over 200 breeding birds. This data is being used to inform coastal zone planning and environmental impact assessments and to design a municipal reserve for the species.
Following a pattern found in many taxa, least terns in Mexico lay two eggs each year, while their counterparts in California lay three. As their potential to recover is limited by their clutch size, least terns in Mexico are more vulnerable to population declines than those in California.
Why, then, does clutch (and, as it turns out egg size) increase with breeding latitude? I am currently looking at clutch mass relative to adult body mass, across 34 species of terns, to consider three possible explanations:
1) Terns nesting at higher latitudes have shorter breeding lifespans, and so invest more at each opportunity.
2) During the breeding season prey is more abundant at higher latitudes, allowing terns to raise more young than in the relatively food-limited tropics.
3) Terns nesting at a given latitude are more closely related to each other than to terns at other latitudes, and the investment trait has been conserved on the phlyogenetic tree.
By looking at trade-offs both in a socio-political and life-history context, I hope to gain experience and provide insight into both avian ecology and management.
