Category Archives: Birds

Double-crested Cormorant Population not at Biological Carrying Capacity

Double-crested Cormorant Population not at Biological Carrying Capacity

Labeling Double-crested Cormorant Population as Overabundant is “Inappropriate”

Scientists Linda Wire and Francesca Cuthburt, of the University of Double-crested cormorantMinnesota’s department of Fisheries, Wildlife and Conservation biology, find that describing the population of Double-crested Cormorants as overabundant is “inappropriate” given historical evidence that this fish-eating bird has  previously been very abundant.

Biological Carrying Capacity vs. Wildlife Acceptance Cpacity

Ecologists often describe the biological carrying capacity as the population limit that a particular ecosystem can support.  Wire and Cuthburt instead discuss the “wildlife acceptance capacity” as the population number desired or tolerated by human society.  They stress that society should aim to maintain bird Double-crested cormorant wings stretchedpopulations at historic levels, and not set population goals based on how they are perceived to help us reach our fisheries goals. Perhaps we need to take a step back and evaluate the contribution of the double-crested cormorant’s activities versus our own activities that impact the fisheries. The cormorants were abundant long before the demise of fish populations.  This is evident upon inspection of the historical records that Wires and Cuthburt have included in their study.   At the very least, we should not claim that this bird is overabundant if there is no evidence that it is at its true carrying capacity.

Human Activities and the Double-crested Cormorant Population

Cormorants have had a reputation as a competitor of humans for fish as far back as 1634.  Wire and Cuthburt cite that there are only a few locations double-crested cormorant swimmingwhere a decline of natural resources have been directly linked to double-crested cormorant populations and that the perceived overabundance is due to the double-crested cormorant populations rebounding closer to their historic levels after recent declines.  The double-crested cormorant population dropped due to the use of DDT from the 1940s to 1970s, combined with population control by humans (legal and illegal methods) and habitat change.    While it may be perceived that the cormorant population has increased, the perceived increase is really a population rebound after a decline due to human activities.  The population along the Atlantic Coast and in the interior of the United States and Canada has rebounded from 32,000 breeding pairs (early 1970s) to more than 226,000 breeding pairs (late 1990s).

 

Future Population Goals

The core issue here is that we need to decide if we should keep our bird populations at historic levels (keep common birds common) or try to reduce population sizes if they compete with us for the same food source.   At the very least, we should not misrepresent their population size to the public as “overabundant” if the historic population size was equal or greater than the current population size.  We need to be honest about the difference between the biological carrying capacity and the “wildlife acceptance capacity”, which is the number that certain human populations think should exist.  That number may have little to do with scientific evidence about how a particular population size affects the rest of the ecosystem.

Find the full study on historic Double-crested Cormorant population sizes here.

 

My New Friend – The Carolina Wren

My New Friend – The Carolina Wren

Thryothorus ludovicianus
Thryothorus ludovicianus

Recording Backyard Bird Songs

A picnic on the lawn with my 2 and 4 year-old  today was filled with sounds of backyard birds chirping, squawking, and calling, but there was one call in particular that gave me an idea.  “Hey kids, do you want to try to record that bird sound?”  I later discovered it was the song of the Carolina Wren.

In a few moments, the kids and I were lying on the picnic blanket plugging in a microphone and headphones into my laptop.  After, the initial disciplining to get the kids to stop tugging back and forth at the microphone and headphones, our recording adventure began….but wait….no bird calls anymore.

I was saddened to think that in the few minutes I had left to go inside, that the bird left too…but then I heard it again.  After playing with the audio device settings on the laptop, and trying to entertain the kids away from the microphone, I successfully recorded our first bird call.

Bird Behavior: Response to Hearing Their Song

The kids and I played it over and over again.  I told them they were biologists and ornithologists today – they were thrilled.  Then, the most amazing thing happened.  This little bird kept flying back and forth over our picnic blanket, sometimes coming within feet of us.  It flew from a tree branch to our shed, from our neighbors shed, to our rooftop, from another branch to our nearby lawn chair…stopping every now and then to repeat it’s song back to us.  Every time we played the song back to the little bird, it flew over us again, daring to fly closer and closer to us with each pass.  We were communicating somehow.

Species Identification: Carolina Wren Song

Later on that evening, thumbing through my favorite field guides, I discovered that my new friend was the Carolina Wren, a native bird to Connecticut, Rhode Island, and Southern Massachusetts that is expanding its range northwards.  Many sources claim that it is a shy bird that is more often heard than seen.  It’s true that I first heard the wren, but once I started playing back its tune, it was anything but shy – truly amazing.

Try at Home: Attracting Songbirds – The Carolina Wren Song

Try playing this bird call in your own backyard to see if any Carolina Wrens come to visit you.  I played it again the next day for my husband and without fail 2-3 Carolina Wrens came to visit us.  They flew back and forth always passing near to us and stopped to perch on nearby branches to sing us their song.  If this works for you, please leave a comment below to let us know.

Great Blue Heron

This Great Blue Heron was filmed and photographed on an après work canoe paddle at Jacob’s Pond in Norwell, MA. The Great Blue Heron has great size and stature at 4’ tall. I highly recommend this pond for anyone looking to see wildlife by canoe or kayak.

Despite the heron being so large, it easily takes off from the water and doesn’t seem to care that it’s 6’ wide wingspan is pushing though tree branches. They wait motionless on their stick-like legs in the water or slowly stalk their prey before they ambush them. They swallow their prey whole, rather that be fish, frogs, or even rodents. You may find that they show up at your backyard koi pond so beware..

There is no sexual dimorphism, meaning that the males and females look the same. Their backs and wings are a bluish-grey. Their neck is brownish-cream and has a scruffy appearance. Their face is white. They’ve got two black stripes above their eyes, and the middle of their crown is white.

This bird can be found around freshwater or brackish water habitats all over New England and into Atlantic Canada. The Great White Heron in Florida was thought to be a separate species, but it is now accepted that they are the same species with different coloration.

I hope that all of you can also add the Great Blue Heron to your own species list. Please visit myspecieslist.com and click on Blue Heron to add your own sightings to our range maps or tell us about them in our comment section. Check our other pages on species from around New England and Atlantic Canada.