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Post date: Oct 13, 2017 3:04:31 PM
Hello, internet! With no fieldwork to do, it's hard to come up with the kinds of photos and stories that motivate good blog entries, but the subterranean work of analysis and writing continues apace.
I recently started a new position at the University of Rhode Island working with tracking data from sea ducks, so I'm only a part-time pelican hobbyist now. Fortunately, there are several new and continuing research projects focusing on pelicans in the Gulf and South Atlantic Bight, so I'm confident that the pelicans won't be neglected in my absence. In the meantime, I'm figuring out some exciting new modeling approaches for the sea duck data, which I'll talk about as soon as I can pull together some results.
I'm mostly poking my head up to highlight three recent papers that have come out of our pelican research (making five total, which is exactly half of what I'm expecting to publish... oof). The cast, in order of appearance:
- Influence of density-dependent competition on foraging and migratory behavior of a subtropical colonial seabird (Ecology and Evolution). Chapter 3 of my dissertation. You may have seen this paper in graphic novel form at this year's World Seabird Twitter Conference. It's also the reason that a photo of Philip Ashmole was hanging over my desk for several years (I may or may not have had conversations with the photo while writing the article). Ashmole originated the idea that seabirds compete for resources around colony sites, resulting in localized prey depletion, and that this process helps limit seabird breeding populations and total population numbers. Anyway, the main take-home message here is that the number of pelicans at a breeding colony influences not only how far individuals travel to feed themselves and their nestlings (showing that localized prey depletion likely exists), but also whether and how far they migrate during non-breeding. Birds from larger colonies travel farther to forage, and migrate farther as well. In fact, the size of the breeding colony is one of the strongest predictors of movement and migration, and individuals that are smaller (and thus less dominant) are the most strongly affected by colony size.
The relationship of colony size to the proportion of migrants at a colony (a) and distance migrated (b)
- Diet composition and provisioning rates of nestlings determine reproductive success in a subtropical seabird (Marine Ecology Progress Series). This is Chapter 5 of my dissertation, and it's a big one, summarizing all the work we did collecting and drying fish. You may have heard this story before (during the World Seabird Twitter Conference, for example!), but the short version is that for pelicans it's not prey quality, but quantity, that matters. The frequency and mass of meals fed to chicks determined nestling survival fledging success, whereas energy content of the meals didn't make much of a difference. Some of the poorest-quality foods-- small forage fish like juvenile Gulf menhaden-- were associated with high fledging rates because they could be delivered frequently and in large amounts. We affectionately nicknamed this pattern the "whale-ican theory." Whales, which capture large volumes of prey at a time, also tend to choose less energy-rich prey than other marine mammals that pursue and capture single prey items. In both their foraging strategies and indifference toward prey energy content, pelicans seem to be the whales of the seabird world. Just wait... it'll catch on.
Rather than selecting Gulf mehaden, pelicans foraged on menhaden in relation to their availability. Dark pies are adult and juvenile menhaden; light pies are other prey; and the solid yellow area is the core range of Gulf menhaden.
- A bridge between oceans: Overland migration of marine birds in a wind energy corridor (Journal of Avian Biology). [Abstract only-- let me know if you want the full text!] This paper has been a long time coming. It developed from some conversations at past Waterbird Society meetings, in which several of us working in the Gulf of Mexico described similar patterns of marine-associated waterbirds migrating over land, from the Atlantic to Pacific ocean basins, across Mexico's narrowest point at the Tehuantepec Isthmus. Our work is descriptive and involves a small number of birds, but it's also important because this part of Mexico is undergoing rapid development for wind energy. Understanding what migrants are passing through the area, and when, is important to insuring that the effects of wind turbines are accounted for. Plus, it's a pretty cool new migratory route for species that are typically thought not to travel long distances over land! Since we put the paper together, David Newstead at Coastal Bend Bays and Estuaries Program has also documented Black Skimmers using the same route, so I'm sure this isn't the last we'll hear of this story.
Migration routes of reddish egrets (top), brown pelicans (middle), and red knots (bottom) across the Tehuantepec Isthmus, Mexico. Fall routes are orange; spring routes are green.
Other recent pelican-adventures have included serving on a panel helping to select a new waterbird colony site in Matagorda Bay, Texas, and presenting at the Waterbirds conference in beautiful Reykjavik, Iceland.
Gratuitous Reykjavik photos...
Next week I'll be traveling to Oilapalooza in Monterey, CA, to discuss the results of our tracking work after the Refugio oil spill. That manuscript should be the next to come out, so stay tuned!
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