For nearly 25 years, I have studied shorebird ecology. I began my graduate research with Dr. Lewis Oring at the University of North Dakota, where I studied various aspects of the sex-role reversed mating systems of Wilson's Phalarope and Spotted Sandpiper. When I came to Humboldt State University in 1989, I realized the tremendous research opportunities that existed in and around Humboldt Bay. Accordingly, I have continued to use shorebirds as model organisms to examine the consequences of individual behavior to population and community ecology. Throughout my research career at HSU, my students and I have applied the knowledge we have gained to conserve and manage populations of shorebirds, and the habitats they occupy.
Roosts and flocking behavior are conspicuous aspects of the nonbreeding ecology of most shorebirds, especially in coastal habitats where tides predictably inundate tidal foraging habitats. Since 2001, my students and I have documented variation in roost use by shorebirds around Humboldt Bay using bay-wide surveys, and by studying radio-marked Dunlin. We've learned that roosts are numerous (and don't appear to be a limiting feature of wintering habitat); only a small proportion of roosts are used consistently. During the day, Dunlin typically roost near tidal habitats of the bay, and they readily move among roosts from one day to the next. At night, however, individuals are found more consistently in the same roost, which typically is located in pastures several kilometers from the tidal flats. For details, see Conklin and Colwell 2007a, Conklin and Colwell 2007b.
The Western Snowy Plover is listed as threatened under the U.S. Endangered Species Act. Since 2000, I have worked collaboratively with biologists at Mad River Biologists to monitor the population of plovers that breeds in Mendocino, Humboldt and Del Norte counties, California. Our studies have shown that this population is relatively stable, and maintained by immigration from elsewhere along the Pacific coast. Additionally, the reproductive success of local plovers is poor, especially on ocean beaches where human activity, native predators of eggs and chicks, and introduced plants compromise productivity. By contrast, plovers breeding on gravel bars of the lower Eel River have high reproductive success, probably owing to low human activity and the cryptic nature of substrates that hides nests and chicks from predators. For details, see Colwell et al. 2005.
Snowy Plover nest on sandy substrates of the Eel River Wildlife Area
On gravel bars of the Eel River, Snowy Plover nests are quiet cryptic
Humboldt Bay is the most northerly wintering site for significant numbers of the Long-billed Curlew, the largest North American shorebird. My students and I have shown that several hundred curlews are present from mid-June into April; some individuals over-summer locally as well. Across Humboldt Bay, curlews are patchily distributed in areas near their roosts and where substrates support their prey. During summer and fall, some curlews defend territories in intertidal habitats where they feed on polychaetes, decapods, bivalves and fishes. With the onset of winter rains, however, individual residency on these territories diminishes and a portion of the local population shifts to feeding in pastures on worms and other invertebrates. For details, see Mathis et al. 2006, Leeman et al. 2001, Leeman and Colwell 2005.
I maintain a longstanding interest in avian breeding ecology. Egg-laying is an important facet of reproductive biology that varies among and within species. Recently, I published a review article that showed that the minimum laying interval between consecutive eggs in shorebird clutches was either 1 or 2 days, although these minimum intervals certainly lengthen during periods of inclement weather. Interspecific differences correlated better with a species' breeding latitude (i.e. species breeding at northerly latitudes typically lay at daily intervals compared with temperate or tropical taxa). Additionally, species such as sandpipers that nest in vegetated habitats that conceal the eggs and adult tend to lay at daily intervals compared with plovers, which nest in the open. This suggests that risk of clutch loss (to predation, or other environmental causes) influences laying intervals. There was no relationship between egg (or clutch) mass and laying interval. For details, see Colwell 2006.
Wetland habitats are among the most threatened worldwide, and waterbirds are especially reliant on wetland resources for survival and reproduction. My students and I have worked in managed wetlands of the northern San Joaquin Valley and the rice fields of the Sacramento Valley to understand how water levels can be manipulated to accommodate diverse assemblages of waterbirds. Additionally, I remain interested in the consequences of human degradation of wetland habitat quality via disturbance, aquaculture, and development. For details, see Connolly and Colwell 2005, Taft et al. 2002.