Did you know that you can learn a lot by what is on the ground at the base of a heron’s nest tree? A heron nest is only so big, so there’s no room for food remains and other forms of heron “trash”. Herons simply just pitch it all over the edge. Out of sight, out of mind, I guess. Light blue eggshells with some membranes in tact indicate a successful hatch; but you may also find remains of young herons that met their premature demise by falling to the ground. Adult feathers that were molted are often found. You might find out that crayfish is a favorite food of the family above. This disposal area for the herons nesting above can really be a treasure trove to a researcher trying to find out how dam removal affects the birds that use a river.
Erynn Call is a PhD student at the University of Maine in Orono. Her research is trying to answer a fairly complex question: How will the Penobscot River Restoration Project impact the river bird community? For those of you unfamiliar with the restoration project, it is aiming to restore 11 species of sea-run fish to the Penobscot River, while maintaining hydropower energy production. In order to accomplish this, the Penobscot River Restoration Trust has purchased and will remove the two lowermost dams on the Penobscot River, Veazie and Great Works, and has purchased and will decommission a third dam, Howland Dam, where a fish bypass will be constructed.
So what does a heron’s trash have to do with it? In Erynn’s words:
“Understanding the feeding and habitat relationships of various species is a key to unraveling ecosystem function and thus is critically important in discerning responses to human impacts…Many bird species rely on the river system and can be linked to the river food web as omnivores, insectivores, and of course, piscivores (fish eaters)…This study examines community dynamics of riverine birds and their interactions with dams and river habitat variation…The ultimate goal…is to quantify how bird assemblages respond to…dam removal and the subsequent restoration of spawning diadramous fishes.”
Among several objectives of the study, Erynn aims to evaluate the relative importance of marine-derived nutrients to riverine birds such as the great blue heron, bald eagle, osprey, and belted kingfisher. Bird samples (blood, feathers, bones) and bird prey items will be collected within inland and coastal areas in Maine with particular emphasis on the Penobscot River ranging from East Millinocket to Bucksport. Stable isotope analysis of the collected materials will reveal the diet and habitat of the animals at the time of their growth. Results will provide an important baseline to examine how the diets of great blue herons and other fish-eating birds shift in response to the restoration of sea-run fish to the Penobscot River.
For this reason, Heron Observation Network volunteers have been asked to visit the colonies they’ve adopted sometime this fall to collect any “heron trash” they can find beneath the nest trees. Unfortunately, most of Maine’s great blue heron colonies are located within wetlands where the nest trees are surrounded by open water, not allowing for materials to collect at the base of the tree. Thus materials will only be collected from colonies in uplands or from those that contain individual nest tress that are on somewhat dry ground. Samples will be placed in Ziploc bags labeled with the colony number and location and shipped to myself or Erynn Call for eventual analysis. I expect that as sea-run fish return to the river, their remains will also be seen in higher abundance beneath great blue heron nests. We’ll just have to wait and see.
In the meantime, check back here for updates on this aspect of Erynn’s research, or learn more about the Penobscot River Restoration Project.