El Niño early winter part 2 - Bird Impacts
by Gerry Smith
The non-winter of much of November-December 2015 was a double edged sword for much of the natural world. Survivorship for many birds may be enhanced, but lack of snow cover and warm temperatures have their down sides. Many insects were about that should not have been. Ticks remained active and were the bane of all critters coming in contact with them. Weather and climate make all aspects of the natural world more complicated and interactions complex. As noted in the previous article, the primary cause of this mild winter is a Godzilla El Niño in the Pacific Ocean. Whether this natural event has been intensified by climate change is a matter of conjecture. Whatever the cause, the effects on different species of birds vary greatly.
For species that are ground feeders, such as Dark-eyed Junco and Wild Turkey, lack of snow cover makes food readily available. Rodent hunting birds of prey, like Rough-legged Hawk and Short-eared Owl, do not have to plow snow to reach their prey. Even though dark colored small rodents blend well with wet, dark soil, sharp-eyed raptors can usually see them. Waterfowl benefit from availability of more habitats with available food. In severe winters, when they are concentrated in limited remaining open water, these species may run out of food and starve to death. Additionally, disease can spread rapidly thorough these concentrated waterfowl fleshpots. A flip side of this is that in mild winters young Bald eagles may have a harder time surviving if meals of weak or wounded waterfowl are not readily available. These inexperienced, and often quite incompetent hunters, never miss a chance for an easy meal. Many “half hardy” species, such as White-crowned Sparrow and Hermit Thrush, may be lulled into remaining north of their normal range by mild fall and early winter weather. These birds are unable to leave if severe weather develops, thus leading to them being sorted out of the gene pool.
While fluctuations in winter weather are “normal,” the degree and frequency of these variations greatly affects birds and their populations. We understand some impacts, while others are more subtle. Severe winters in the east, like those of the last two years, can hit North American continental wintering species hard. Freezes very far south in the winter of 2014-15 greatly reduced Tree Swallow populations, something that was very obvious this past summer. Impacts of mild winters are generally less obvious for many species but “short-stopping” in migration and changes in migration schedules can adversely impact species. Our birds evolved with a fluctuating but generally predictable weather and climate regime. Major changes in this regime may impact the ecology of a species in ways we cannot predict. While many people assume that mild seasons are better for most bird seasons than severe ones, we cannot always be sure. Stay tuned.