Mark Colwell


Dr. Mark Cowell
(707) 826-3723

Shorebird ecology, management of wetlands for shorebirds, refuge design. Courses include: Ornithology, Conservation Biology, Management of Shorebirds, Birds and Human Society.


My primary goal in teaching is to inspire students to learn more about the natural world, whether it be through a simple understanding of the biology of a bird or the complexity of ecological theory. I attempt to instill in students the importance of gaining factual knowledge, such that they will possess enhanced abilities to make wise decisions regarding conservation of earth's natural heritage. And, I expect students to be able to communicate their knowledge effectively, to me, other scientists, and the public.

To accomplish this, I have designed many of my courses with a healthy dose of field exercises to instill in students an appreciation for the natural world while expanding their ecological knowledge. These experiences often serve as direct links to material presented in lectures. My approach to teaching varies with the target audience (i.e., general education, junior-level wildlife majors, advanced undergraduates, and graduate students). For instance, in my summer GE course (Birds and Human Society), I motivate students to open their eyes to the natural world around them and to appreciate how the everyday life of birds relates to humans (via food, recreation, disease). In my junior-level classes (Principles of Wildlife Management), I instill an appreciation for theory, its relationship to empirical knowledge, and its application to real world circumstances, such as predator control in Alaska. And, in advanced courses (Shorebird Ecology and Conservation), I emphasize the primary literature and attempt to have students apply ecological knowledge to management and conservation scenarios that they have experienced in and around Humboldt Bay (conservation of Snowy Plovers, oyster-culture impacts on intertidal habitats). These various courses represent a "stepping stone" of expectations for students with varying backgrounds, interests, and professional aspirations. Regardless of the class, however, I expect students to master material such that they can communicate effectively their knowledge of a subject and make intelligent decisions regarding management and conservation of wildlife.

I love to teach, and I think I do so with enthusiasm. This may be the most important facet of my approach to share with students my appreciation for the wonder of the natural world, and its value to humans.


Post-Doctoral Research Associate, University of North Dakota 1987-1989
Ph.D. Biology, University of North Dakota 1987
B.A. Biology, Whitman College 1979

Courses Taught

Birds & Human Society
Shorebird Ecology, Conservation & Management
Conservation Biology
Principles of Wildlife Management
Wildlife Ecology & Management


For nearly 35 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 Cal Poly Humboldt 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 Humboldt, 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.Colwell et al. (2017). 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.

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.

Prospective Graduate Students

If you are a prospective graduate student and wish to inquire about graduate education working with me at Humboldt, here are a few things to consider before you contact me. First, have a good idea of what intrigues you in the field of ecology, and how these interests mesh with my research program. Although I have conducted much of my research with shorebirds, I am open to (and have advised) students working on other taxa (e.g., Common Raven, White-faced Ibis, waterfowl). My students have worked on topics ranging from habitat use, space use, population models, and survival analyses. Second, when you enquire about graduate research include a polished proposal of what you would like to study. Third, make sure you have addressed any academic and professional deficiencies. For example, take the GRE (and score well!), and make sure you have no academic deficiencies in the sciences (i.e., chemistry, genetics, calculus, etc.). Also, it is extremely helpful to have field experience before starting graduate school. Most students I have accepted have several years of experience prior to enrolling at Humboldt. Finally, be committed to continuing your education, and in doing so with diligence and devotion.

I expect students to become experts in the area of ecology related to their thesis topic such that I learn a little from them. Lastly, I have a strong reputation for supporting my graduate students, whether directly in fieldwork or by promptly turning around proposals/theses.

List of previous graduate students

Former Graduate Students

Name Thesis
Alexis Dejoannis
Teresa King



View 2004 - 1986 publications »

Presentations at Professional Meetings

I regularly present and co-author papers at regional and national meetings. For example, in 2006-07, I co-authored 9 papers with students at three CA meetings: 1) Western Section of The Wildlife Society, Monterey; 2) Pacific Seabird Group, Asilomar; and 3) Society of Wetland Scientists, Sacramento.