![]() For avian consumers like passenger pigeons that must swallow their food whole, maximum gape size constrains dietary range ( Wheelwright, 1985). Due to their great abundance, passenger pigeons are commonly assumed to have consumed seed crops in their entirety, although this assumption neglects the morphological constraint of bill gape size. The adaptive response by trees to seed predation depends on the number and size of seeds eaten. The negative impacts of consumers on their prey (e.g., reduced fitness) can lead to an evolutionary arms race of defense and resistance, whereas positive effects (e.g., dispersal) may select for mutualisms ( Ehrlich and Raven, 1964 Howe and Smallwood, 1982 Hererra, 1985 Thompson, 1994) In the case of mast bearing trees, responses to negative impacts (the destruction of seeds) include predator satiation, asynchronous masting, alteration of germination timing, changes in seed size, and chemical defenses ( Janzen, 1971 Loehle, 1987 Vander Wall, 2001). These differing ecological roles have distinct evolutionary implications for the forest ecosystem both before and after the passenger pigeon's extinction. seed dispersers (mutualists that disperse seeds) is unknown. However, the degree to which passenger pigeons functioned as seed predators (consumers that destroy seeds) vs. Historic observations and analyses of crop/gut contents indicate that passenger pigeon's dietary range included most if not all species of seed-bearing trees ( Cottam and Knappen, 1939 Schorger, 1955 Greenberg, 2014). Arguably the most significant interactions were between the pigeons and their primary prey-masting and seed bearing trees ( Webb, 1986 Ellsworth and McComb, 2003). The ways in which passenger pigeons shaped whole ecosystems and/or individual species within forest communities depend on the nature of the bird's relationships with those species. Various hypotheses have been advanced for how these megaflocks shaped the distribution and abundance of tree species ( Webb, 1986 Ellsworth and McComb, 2003) however, most of these hypotheses lack convincing evidence and long-term eco-evolutionary forces imposed by passenger pigeons lack attention almost entirely. Our results highlight the range of ecological interactions that can be lost with species' extinction and the inherent challenge of understanding the consequences of those interactions.įor tens of thousands of years prior to their extinction in the early twentieth century, passenger pigeons ( Ectopistes migratorius) were the most abundant bird species in North America, moving nomadically, consuming mast, and fruit crops throughout eastern forests in megaflocks containing tens of millions to billions of individuals ( Greenberg, 2014 Murray et al., 2017). ![]() In addition, we conclude that the digestive process invariably destroyed consumed seeds but the potential for a nutrition/dispersal mutualism might still have existed via regurgitation and post-mortem release of crop contents. Our findings suggest that the passenger pigeon's dietary range, observed historically to be taxonomically broad, was constrained to certain seed sizes due to bill gape size. Using the band-tailed pigeon ( Patagioenas fasciata) and the rock dove ( Columba livia) as physical and ecological proxies, we evaluated passenger pigeon dietary range and potential to disperse seeds. Here, we strive to better understand what was probably one of the most significant of these interactions-that between passenger pigeons and seed bearing trees. The extinction of passenger pigeons in the early twentieth century undoubtedly influenced associated species and ecosystems as interactions stemming from the pigeons disappeared suddenly. 3VCA San Francisco Veterinary Specialists, San Francisco, CA, United Statesįor tens of thousands of years, passenger pigeons ( Ectopistes migratorius) were a dominant member of eastern North American forest communities, with megaflocks comprising up to several billion individuals.2Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, United States.1Revive & Restore, Sausalito, CA, United States.
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