2005 NYCA Harbor Herons Monitoring Program

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2005 Mid-season Summary

 

by Chris Nagy

 

Wetland wildlife has had a rough time for the last century.  By the 1980’s (15 years ago), the wetland habitat in the lower 48 states has decreased to less than 53% of its original area.  In addition, intense pesticide and fertilizer use has reduced the quality of this remaining habitat and affected the abundances of many species.  This includes, of course, wetland wading birds such as herons and egrets.  However, for approximately the last twenty years, New York Harbor has contained a number of wading bird nesting colonies.  This is largely due to the Clean Water Act of 1972 and the preservation of these small islands as non-developed areas.

While the birds nest on the islands because of the woody vegetation and relative isolation from human disturbance, they forage in the salt marshes and freshwater swamps in the greater metropolitan area.  Therefore, the foraging grounds must be preserved along with the nesting sites if we wish to have these species in our area.

This is NYC Audubon’s third year monitoring the wading bird colonies in New York City waters, and it is our most ambitious and exciting season yet.  The objectives of the Monitoring Program have been to document the daily activity patterns of the birds at each colony and to attempt to determine the important foraging grounds used by birds of each colony.  By linking individual colonies with the respective foraging grounds, we can provide important information that will allow us to better protect the wading birds of New York City.

To this end, we spend four days each week collecting data at four different wading bird colonies: Hoffman Island, east of Staten Island; Canarsie Pol, in Jamaica Bay; Brothers Islands in the East River; and Goose Island, near Pelham Bay Park.

Observations of every bird (of the target species) that enters or leaves each colony are recorded, along with the direction of flight.  These data have been collected for the last three years almost entirely by dedicated Audubon volunteers, and have built up an important database of information.

However, until 2005, every monitoring session could only be done from the shore of the mainland.  Hence, only roughly half of the island was observed, and we did not know how much bird traffic was occurring on the far side of the islands.  It was thought that the far sides would be less used than the shore sides, but this assumption needed to be tested.

This year, we have been conducting monitoring session from boats, allowing us to get to the far sides of each colony and record bird movements from these directions.  At this point, it looks like there is somewhat less movement to and from these sides, but certainly they are being used.  We’ve counted well over 400 birds in our first month and a half.

In addition, we’re taking a few trips in the Fuji blimp, to hopefully spot egrets and herons as they “commute” to get more direct data pertaining to their selection of foraging grounds.

We’ve looked at some of the data, and can present a few of our results.  The following is a graph showing percentages of the total flights in each direction at Hoffman Island ( up to 6/29/05; BCNH = black-crowned night heron; GREG = great egret; SNEG = snowy egret; GLIB = glossy ibis):

It looks like the majority of the flights have been towards the west and southwest.  However, these data have not been corrected for the amount of time spent observing each side.  We will likely weight each direction by the amount of time that octant of the compass was observed.  At Hoffman, this will likely not change our results very much (there is a pretty clear tendency towards west and southwest), but at other colonies, such as Brothers, weighting may illuminate some unexpected patterns.

Here is the same type of graph for Goose Island (up to 6/29/05; YCNH = yellow-crowned night heron):

We hope to use these data to narrow down the list of likely foraging grounds that are used by birds of each colony.  It would be very useful to know which marshes birds from a particular colony use.  Changes in the dynamics at a colony could be due to factors present at the foraging grounds.

 

As we approach the end of July, activity at the colonies will be winding down as the young birds find their wings, and the birds leave the colonies to spend all of their time at the foraging sites.  Therefore, in August we are planning on having a number of field trips to the foraging grounds to monitor birds there.

 

If you are interested, our weekly updates are on this website <a>here</a>.  More data will be made available as it comes in.  As well, please contact me if you are interested in volunteering.  You do not need to be a bird watching expert to volunteer.