White River Rookery Survey

On April 26, 2014 I accompanied Karl Werner, Rob Rutledge, and Mike Clay to survey the White River Heron Rookery in NW Johnson County. The rookery is on CILTI property (Central Indiana Land Trust Incorporated) on the west side of the river and is not open to the public. The goal is to census the Heron Rookery every five years. The census should have taken place last year, but high water prevented the count.

Heron Rookery - Map

Heron Rookery - Satellite

The day was perfect for the census. We surveyed the rookery in mid-afternoon under clear skies which was good since the temperature reached 80 degrees Fahrenheit.  That is important since some of the Great Blues fly off the nest uncovering the eggs.  But the warmer temps should have kept them warm for the short time they were exposed.

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One of the active nests we observed through the limbs.

We worked quickly going in a north-south pattern marking the counted trees so we wouldn’t tally them again. We probably weren’t in the main part of the rookery for more than 45 minutes.

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It was very easy to get disoriented if you didn’t try to stick to a constant back and forth walk.

Listed below are the results of this and previous years survey:

Year            Total Nests        Active Nests        Number of Trees
1985                   142
1987                   225
1990                   334
1993                    562
1998                    505
2003              314                    300                        ?
2008 (4/18)    146                    138                        51
2014 (4/27)     89                     85                          36

So why the increase and then decline in the number of nests over the years? I turned to the internet to see what others have speculated on the declines of rookeries. Some of the reasons I found were disturbances in food source, water pollution, eagles in the area taking eggs, a nearby loud noise, or simple an overpopulation of the area.

One of the things I thought about was the growth of the city of Greenwood which lies to the east.  Below is the population growth of Greenwood.

1980     19,327     62.8%

1990     26,265     35.9%

2000     36,037     37.2%

2010     49,791     38.2%

I have only lived in the area a short time, so I don’t know if the city’s expansion effected the herons or their food supply.  But last year I was out observing the rookery from the east side of the river.  The owner of the only house in the area stopped by to talk.  He said the house had been his grandfather’s so he had been coming to the area for years.  He remembered as a child the herons flying all day long to somewhere “east” and then returning.  Presumably with food.  Over the years he had watched the number decline with greater decreases over the last 5-10 years.  He speculated the expansion of gravel pits in the area might have something to do with it.  In the couple of hours I spent there I only saw four herons flying east and then back. So I can’t think that the city’s growth couldn’t have impacted the rookery in some manner.

As for other reasons listed, yes there are Bald Eagles that live on that stretch of the river. The large gravel pits have loud, noisy machinery.  Maybe the composition of the White River has changed.

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A view of the White River looking north of the rookery. Notice all the debris from the recent flooding.

My theory, which I have no proof or facts to back up, is there got to be too many herons for the local food source.  There would have to be over 1000 herons if there were 562 nests, plus the young.  There would have had to been a large supply of food to support that many herons. So hopefully many of the herons moved on to other locations with a better food source.

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A couple more nests. I’m not for sure but these might have been abandoned.

But like most things I have encountered in life, it is probably a combination of several things.

It would good to hear from others about the rise or decline of other heron rookeries.

Thanks to John Castrale for providing the data on past surveys.

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