Hawk migration count

White Memorial's hawk count   
     As autumn approaches, many bird species that breed in the northern United States and Canada begin their yearly journey south.  White Memorial is contributing to the Hawk Migration Association of North America's yearly hawk count.  Our hawk counting station is located near the observatory (a green, shed-sized building) on Sawmill Field.  Volunteers who are interested in taking part are encouraged.  Data sheets and raptor silhouette ID sheets are located hanging from a nail inside the cellar door on the side of the museum.  If you choose to be a part of our hawk count, please bring binoculars, watch from near the observatory, and return the sheets to the cellar when you are finished.  To see our data, check out our site data on hawkcount.org.
How hawks migrate
     When migrating, birds of prey rely on thermals, or columns of rising hot air.  They circle upwards, using the thermal for lift to save energy.  Once they reach their desired elevation, they leave the thermal and soar southward, gradually losing elevation until they reach another thermal.  Many raptors wait until the wind is coming from the north so that it pushes them south.  Ideal days for migration are sunny and clear, with wind blowing from the north or northeast.  On ideal days like that, spots where thermals form can get very busy, with many hawks circling upwards in the same thermal.  This occurrence is called a kettle of hawks.  Identifying and counting hawks in a kettle can be difficult, and it is recommended that individuals are only counted as they leave the kettle.
A kettle of hawks, mostly broad-wings, from HMANA.org
Why count hawks?
     Many hawk species have experienced a steep drop in population since the advent of the pesticide DDT in the 1940s.  DDT worked its way up the food chain through insectivorous birds and mammals, and fish when the chemical leached into streams.  Since all of their prey species were full of DDT, the toxin bioaccumulated in the bodies of raptors.  This caused them to lay eggs with shells so thin that the weight of the parent birds warming them would cause them to crumble before chicks could fully develop. Since DDT was banned in the 1970s, many species have made incredible comebacks, while others are still in trouble because of other factors like habitat loss.  By keeping track of the number of raptors that pass through during migration every year, HMANA will notice fluctuations in the populations and be able to respond if need be.

Notable sightings so far this year

  • Several crows attacked a Cooper's hawk as it tried to enter the thermal.  Rather than making a speedy getaway as hawks usually do, this one fought back, showing off its incredible accipiter agility, dodging and diving at the crows.
  • A pair of adult bald eagles kettled together 
  • A juvenile golden eagle entering the thermal shortly after a juvenile bald eagle made a mock attack at the bald eagle while passing it.

Small mammal trapping to determine tick burdens on Lyme disease reservoir species

     We have been setting nonlethal traps on sixteen plots throughout the property to catch small mammals.  Traps are set for three consecutive nights, and are checked early in the morning.  Each small mammal is weighed, measured, and tagged on the ear with a unique identification number that allows us to recognize individuals that have been caught more than once.  The main objective of our small mammal trapping project is to determine the tick burden the mammals are carrying. This late in the summer, we are most likely to encounter larvae, although we have found that some nymphs are still present.
Left: A tick larva (above my thumb) and nymph (above my thumb and slightly to the
right)  Right: A close-up of the larva (note: larvae have six legs while nymphs and
adults have eight)

     White-footed mice (Peromyscus leucopus) are the most common small mammals we catch, and they are also a major host species for black-legged or deer tick (Ixodes scapularis) larvae and a reservoir for Lyme disease (Borrelia burgdorfer).  In order to pass from one life stage to another, ticks require a blood meal, after which they drop off to molt and must find a new host.  Larvae often attach to small mammals or birds, and if a larva's host is carrying the bacterium B. burgdorfer, that larva will carry Lyme disease and spread it to future hosts.  For more information on the tick life cycle and how they spread Lyme, click here.
     When we catch a small mammal, we count and remove tick larvae and nymphs.  If we catch the same small mammal more than once in a three-day period, it allows us to see how quickly they are picking up new ticks  This can help us understand the abundance of ticks in each area.  Trapping will also give us a better understanding of small mammal subpopulations, demographics, and diversity throughout the property.
White-footed mouse (Peromyscus leucopus) being checked for ticks.
     Most of the ticks we find on small mammals are on the head, especially the ears.  It is estimated that ticks found on the head make up about 40% of the animal's entire body tick burden.  One unlucky individual had 31 tick larvae on one ear and 26 on the other, in addition to carrying a botfly larva.  This was an extreme case, and tick burdens vary from one site to the next.  
     One of the white-footed mice we've caught is a veteran of last summer's mouse over water experiment.  Last year he was caught, tagged, and kept for seven days in an enclosure over water until his ticks dropped off into the water and could be counted.  The mice in that experiment were well-fed and released near where they were originally caught.  This year, he was caught on three consecutive trapping days, and seems to have decided that having an easy meal is worth being handled.  
Trap-happy #46, calmly enduring being handled
     So far we have finished trapping at three of our sixteen sites.  Sadly, we had to say goodbye to #46 and leave him to forage for food like a real mouse.  The data we have gained from this project will be used along with the tick phenology data and earthworm data from the same plots to better understand the relationship between tick populations and survivorship and the presence or absence of invasive earthworms.    

Testing Bantam Lake for potentially harmful cyanobacteria

A cyanobacteria, phormidium (cluster of rods, center), and a zooplankton, Bosmina longirostris (bottom)
     With help from the Northeast Cyanobacteria Monitoring Program, we are reviewing the species composition of the "blue-green algae" in Bantam Lake and other water bodies on the property.  We frequently use the University of New Hampshire's Center for Freshwater Biology for identifying the so-called "Dirty Dozen" species of cyanobacteria, as well as phytoplankton and zooplankton.  Our observations are reported to the Cyanoscope iNaturalist.
     Cyanobacteria are naturally occurring photosynthetic organisms that live within the top ten feet of surface water.  While these organisms are usually harmless and nearly omnipresent, high concentrations of them known as blooms concentrate the toxins they releases.  When this happens, they can cause harm to fish, aquatic plants, and amphibians, as well as terrestrial animals who swim or drink water in which there's been a bloom.  Blooms can be caused by a shift in the nutrient levels in water, like an increase in nitrogen caused by fertilizer runoff.  Blooms usually occur in warm weather.
      The Dirty Dozen are the twelve most commonly observed species of cyanobacteria in New England.  We've sampled water from Beaver Pond, Bantam River, and Litchfield Town Beach, and will sample from several other locations on Bantam Lake.  So far, we've found nine of the twelve.  They are not present in large enough quantities to be harmful, and some, like phormidium, can be indicators of clean water when in normal quantities.  By sampling at Bantam Lake, we are hoping to better understand the community of cyanobacteria present in the lake.  Shifts in the species present could tell us more about water quality and hopefully warn us before a bloom occurs.