June 3, 2015 at 4:16 pm
[caption id="attachment_1263" align="alignleft" width="300"]
This is a typical "fly-by" view of a great blue heron colony. How many nests do you see? (Click image to enlarge)[/caption]
On May 1st, IFW biologists and warden pilots began surveys for great blue heron colonies across the state. These surveys are conducted using warden service airplanes which are flown at low level in order so observers can find colonies and count nests. Once a colony is located, several passes are often required to count the number of active and inactive heron nests at each site. The nests are made of sticks and can be in live or dead trees and occur in uplands, wetlands, and on islands. When nests are in a dense stand of snags (dead trees), their gray color blends in well and can be difficult to count. When colonies are large (in Maine, the largest colony is ~120 pairs), biologists must estimate the number of nests, for there is no way to fly over slow enough to count each one individually. Further, when herons are incubating eggs, their gray bodies are difficult to see against the gray background of the nest.
Despite these challenges, aerial survey is a preferred method for surveying colonies across the state because it is a quick and efficient way to cover such a large area. Over 90% of Maine is forested and therefore considered potential nesting habitat for herons. Instead of attempting to survey every inch of the state, I worked with Mark Otto, a statistician with the U.S. Fish and Wildlife Service, to design a survey specifically for great blue herons. The survey samples two types of randomly selected plots, each 100 km2 in size. The “Area” plots are searched for new colonies and usually take an hour to cover methodically. The “List” plots contain known colonies, and only those known colonies need to be checked for nesting activity. It is the comparison of the results from the Area plots and the List plots that produces a highly accurate estimate for the entire state. The plan is to repeat these surveys at future intervals (e.g. every 5 years) to obtain a population trend.
Since the listing of great blue herons as a Species of Special Concern in 2007, IFW has been working to determine if a decline observed in the coastal nesting population is also happening statewide. Between the mid-1980s and 2009, the number of nesting pairs on coastal islands in Maine dropped 66% from over 1200 to 430 pairs. A statewide comprehensive survey had never been done. In 2009, I started a citizen science program called the Heron Observation Network which enlisted volunteers to monitor known colonies across the state. Their annual monitoring efforts have contributed greatly to our knowledge of the statewide population and this information fed directly into this year’s aerial survey.
To date, 32 hours of surveys have been conducted in southern and central Maine, and four new nesting sites have been discovered. Between now and the end of June, roughly 38 additional survey hours will be needed to complete the survey.
[caption id="attachment_1267" align="aligncenter" width="600"]
Here's the same colony shown above. All visible nests are marked with a red circle. We estimated 19 total nests when we flew over it, so there are 2 hidden from this view. (Click image to enlarge.)[/caption]
To report a great blue heron colony or get involved with the Heron Observation Network, please contact Danielle D’Auria at (207) 941-4478, or danielle.dauria@maine.gov.
This is a typical "fly-by" view of a great blue heron colony. How many nests do you see? (Click image to enlarge)[/caption]
On May 1st, IFW biologists and warden pilots began surveys for great blue heron colonies across the state. These surveys are conducted using warden service airplanes which are flown at low level in order so observers can find colonies and count nests. Once a colony is located, several passes are often required to count the number of active and inactive heron nests at each site. The nests are made of sticks and can be in live or dead trees and occur in uplands, wetlands, and on islands. When nests are in a dense stand of snags (dead trees), their gray color blends in well and can be difficult to count. When colonies are large (in Maine, the largest colony is ~120 pairs), biologists must estimate the number of nests, for there is no way to fly over slow enough to count each one individually. Further, when herons are incubating eggs, their gray bodies are difficult to see against the gray background of the nest.
Despite these challenges, aerial survey is a preferred method for surveying colonies across the state because it is a quick and efficient way to cover such a large area. Over 90% of Maine is forested and therefore considered potential nesting habitat for herons. Instead of attempting to survey every inch of the state, I worked with Mark Otto, a statistician with the U.S. Fish and Wildlife Service, to design a survey specifically for great blue herons. The survey samples two types of randomly selected plots, each 100 km2 in size. The “Area” plots are searched for new colonies and usually take an hour to cover methodically. The “List” plots contain known colonies, and only those known colonies need to be checked for nesting activity. It is the comparison of the results from the Area plots and the List plots that produces a highly accurate estimate for the entire state. The plan is to repeat these surveys at future intervals (e.g. every 5 years) to obtain a population trend.
Since the listing of great blue herons as a Species of Special Concern in 2007, IFW has been working to determine if a decline observed in the coastal nesting population is also happening statewide. Between the mid-1980s and 2009, the number of nesting pairs on coastal islands in Maine dropped 66% from over 1200 to 430 pairs. A statewide comprehensive survey had never been done. In 2009, I started a citizen science program called the Heron Observation Network which enlisted volunteers to monitor known colonies across the state. Their annual monitoring efforts have contributed greatly to our knowledge of the statewide population and this information fed directly into this year’s aerial survey.
To date, 32 hours of surveys have been conducted in southern and central Maine, and four new nesting sites have been discovered. Between now and the end of June, roughly 38 additional survey hours will be needed to complete the survey.
[caption id="attachment_1267" align="aligncenter" width="600"] Here's the same colony shown above. All visible nests are marked with a red circle. We estimated 19 total nests when we flew over it, so there are 2 hidden from this view. (Click image to enlarge.)[/caption]
To report a great blue heron colony or get involved with the Heron Observation Network, please contact Danielle D’Auria at (207) 941-4478, or danielle.dauria@maine.gov.Categories