Potential Effects of Passenger Pigeon Flocks on the Structure and Composition of Presettlement Forests of Eastern North America

Abstract

We considered the possible effects Passenger Pigeon ( Ectopistes migratorius) flocks may have had on the disturbance regime and species composition of presettlement forests in eastern North America. We suggest that the activities of roosting and nesting Passenger Pigeons caused widespread, frequent disturbances in presettlement eastern forests through tree limb and stem breakage and nutrient deposition from pigeon excrement. We suspect that the deposition of fine fuels resulting from such disturbances may have influenced fire intensity and frequency in presettlement forests. Further, we propose that consumption of vast quantities of acorns by pigeons during the spring breeding season may partially explain the dominance of white oak ( Quercus alba) throughout much of the presettlement north-central hardwoods region. Consequently, the pigeon's extinction may have facilitated the increase and expansion of northern red oak ( Quercus rubra) during the twentieth century. Although it is difficult to accurately quantify how physical and chemical disturbances and mast consumption by Passenger Pigeon flocks affected forest ecology, we suspect they shaped landscape structure and species composition in eastern forests prior to the twentieth century. We believe their impact should be accounted for in estimates of the range of natural variability of conditions in eastern hardwood forests.Efectos Potenciales de Parvadas de Palomas Migratorias sobre la Estructura y Composición de Bosques en Norte América Oriental antes de la Colonización Resumen: Consideramos los posibles efectos que pudieron haber tenido parvadas de Palomas Migratorias( Ectopistes migratorius) sobre el régimen de perturbación y la composición de especies de bosques en Norte América oriental antes de la colonización. Sugerimos que las actividades de perchado y anidación de las palomas causaron perturbaciones frecuentes y extensas en los bosques orientales antes de la colonización por medio de la ruptura de ramas y tallos deárboles y la deposición de nutrientes del excremento de las palomas. Sospechamos que la deposición de combustibles resultantes de tales perturbaciones pudo haber influido en la intensidad y frecuencia de incendios forestales. Más aún, proponemos que el consumo de grandes cantidades de bellotas por las palomas en la primavera puede parcialmente explicar la dominancia de roble blanco ( Quercus alba) en muchos de los bosques nor-orientales. En consecuencia, la extinción de la paloma pudo haber facilitado el incremento y expansión del roble rojo ( Quercus rubra) durante el siglo veinte. Aunque es difícil cuantificar con precisión como las perturbaciones físicas y químicas y el consumo masivo por parvadas de palomas migratorias afectaron a la ecología forestal, sospechamos que modelaron la estructura del paisaje y la composición de especies en los bosques orientales antes del siglo veinte. Creemos que su impacto debería ser considerado cuando se hacen estimaciones del rango de variabilidad natural de las condiciones en bosques orientales de maderas...

Experimental Investigation of the Dietary Ecology of the Extinct Passenger Pigeon, Ectopistes migratorius

“…In agreement with previous hypotheses, we find that passenger pigeons were primarily seed predators (Janzen, 1971;Ellsworth and McComb, 2003) although they may also have contributed to seed dispersal (Webb, 1986;Aizen and Patterson, 1990). We also identify physical limitations of passenger pigeon gape that would have affected their ability to consume and disperse the largest seeds of eastern North American tree species.…”

“…After noting an overlap in white oak dominance in regions of spring-time pigeon occurrence, Ellsworth and McComb (2003) hypothesized that the autumn germination of white oaks allowed them to escape spring time predation by pigeons, further allowing white oaks to dominate over red oaks in northern areas commonly occupied by passenger pigeons during spring months. These authors interpreted a shift in dominance from white to red oak after the passenger pigeon's extinction as further evidence in support of their hypothesis.…”

“…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.…”

“…Arguably the most significant interactions were between the pigeons and their primary prey-masting and seed bearing trees (Webb, 1986;Ellsworth and McComb, 2003). 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).…”

Drastic population fluctuations explain the rapid extinction of the passenger pigeon

“…In one of many illustrative descriptions, John James Audubon recounted a mile-wide flock of migrating passenger pigeons that passed overhead, blocking the sun for 3 consecutive days (9). The vast numbers of passenger pigeons have led ecologists to suggest that this bird was a keystone species in North American ecosystems (10,11). This pigeon is believed to have influenced forest composition by consuming and dispersing acorns, beechnuts, and other mast crops on which it fed (10, 11), disrupted local communities, out-competed other mast-eating species, damaged trees by the weight of large flocks leading to breaking of large limbs of trees, and killed surface vegetation with thick layers of excrement (8,11).…”