Great Blue Heron (GBHE) and Great Egret (GREG) Rookery Monitoring - Cibolo Nature ...
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Photo by: Avia Enviro
Skyhawk drone 4.18.19
Great Blue Heron (GBHE) and Great
Egret (GREG) Rookery Monitoring
2019
Donna Taylor and J.W. Pieper
08/05/2019
This document summarizes the data obtained during the 2019 monitoring season of the Great Blue
Herons and Great Egrets located at the Cibolo Preserve in Boerne, Texas.
CIBOLO PRESERVE
GREAT BLUE HERON (GBHE) and GREAT EGRET (GREG)
ROOKERY MONITORING
2019
Rookery monitors: Candace Andrews, Susan Bogle, Coco Brennan, Kenneth Butler, Lisa
Center, Kaye Cosby, Brenda Fest, Gary Fest, Jim Funk, Linda Gindler, Louise Haney, Sarah Hilburn,
Tom and Patsy Inglet, Terry Lashley, Janet Ledbetter-Ferrill, Wendi Leonard, Pamela Louis, Melissa
Marks, Robin May, Paul Mebane, Lars Nielsen, J.W. Pieper, John Prentice, Darla Reid, Wilt Shaw, Pete
and Melissa Shepherd, Jennifer Sorenson, Ron Tietz, Donna Taylor and Darlene Varga.
Rookery Monitored Weekly:
February 5 through July 16, 2019
The “Roadside” tree was the only active rookery this year (Figures 4 & 5). Nest building activity
was not observed in other sites previously known to have had activity.
Fourteen identified nest sites had Great Blue Heron, Ardea herodias and/or Great Egret, Ardea
alba association. Of the fourteen nests A, B, K, N, O, S, T, U and V where previously monitored
while nests W, X Y, Z and aa were added as new nest sites this year (Table 2).
Only seven nests A, B, S, T, U, V and Z were occupied consistently throughout the season and
were observed to have incubated young. Although identified as nests and had adult association,
nests K, N, O, W, X, Y and aa did not produce young.
Eight nestlings and/or fledglings were observed during one monitoring period on May 14, 2019.
Although eight nestlings were observed during this one monitoring event, adding the raw data
high counts per nest for the entire season yields a total of 11 nestlings. A (1) + B (1) + S (2) +
T (1) + U (2) + V (2) + Z (2) =11. All 11 were never observed at the same time. As mentioned
in previous reports there is the possibility that the high counts may inadvertently count an adult
as a fledge or the fledges were visiting another nest. Once the leaves appear, it is sometimes
very difficult to distinguish the differences between an older fledgling and an adult. When the
fledges start moving around it is also difficult to know if they remain in the nest of origin or
“visit” other nests.
As has historically happened, Nest A, the predominant and highest nest in the tree, was the first
occupied with a single adult heron on February 5, 2019. Nest B was first occupied on April 9th
by a heron, with a nestling observed on May 14th. The following week a single adult egret was
occupying the nest and continued to do so through June 6th. No egret young were observed in
nest B.
The team noted egrets standing in nests N and Z beginning on April 2, nest X on April 11 and
nest K on April 25, but nest Z was the only nest with a successful egret nesting pair and fledges.
January 14, 2019 has been set as the training date for the 2019 season.
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Fast Facts:
The earliest observation of adult herons in the Roadside tree occurred on February 5, 2019.
All new nests for 2019 season were named per the same alphabetical nomenclature adopted in 2012.
All letters of the English alphabet have now been identified in the Roadside Rookery Master Nest
Matrix. Because all single letters have been used, we are now using lower case double letter aa.
(Table 2).
The seven nests that successfully produced young were A, B, S, T, U, V (all herons) and Z (egrets).
The greatest number of birds in the tree occurred during week 18, when 15 herons and 4 egrets
(adults and young) were counted (Figure 3).
The last recorded observation of fledglings occurred on July 16, when a single heron fledge was
associated with nest S. Since anecdotal monitoring on the Cibolo Preserve confirmed no further
herons or egrets were at the tree on subsequent dates, July 16 marked the end of the 2019 monitoring
season.
Summary statistics and data comparisons to past years are provided in Tables and Figures on this and
following pages.
Active Nests Fledglings Date of first chick observation
Year GBHE GREG GBHE GREG GBHE GREG
2019 9 5 9 2 April 18 May 16
2018 6 0 5 0 April 5 none
2017 8 0 11 0 March 28 none
2016 8 0 11 0 March 29 none
2015 5 4? 8-10 1 April 28 none
2014 9 1 11 2 March 18 May 20
2013 6 0 4 0 April 16 none
2012 4 0 1(2?) 0 May 22 none
Table 1. Summary statistics for Roadside Rookery
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Roadside Rookery tree = single letters and lowercase double letters
Fern Bank tree = capital double letters at page bottom right. Nest absent Official Name
2012 2013 2014 2015 2016 2017 2018 2019 2020 2021
A A A A A A A A
B B B B B B B B
C C C
D D
E E
F F F F
G G G G G
H H
I I I I
J J J J J
K K K
L L
M M M M
N N N N
O O O O O O O
P P P
Q Q
R R R
S S S S S
T T T
U U U U
V V V
W W
X X
Y Y
Z Z
aa* AA
BB
CC
DD
EE
*lowercase
double =
0 5 9 14 13 8 6 14 0 0 0 roadside tree
Table 2. Roadside Rookery Master Nest Matrix shows the nests built and identified each year
since inception of study at this tree. Once a nest site is identified the name remains with that site
even if a nest is not built there in subsequent years. See nest “C” as example. Nest established
in 2013 was not present in 2014 but appeared again in 2015.
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Cibolo Preserve
Total reproduction results by year
45
39
40
35
30 27
25 24
25
20 18
14
15
10 11 11 11
8 9
10 7
5 5
5 2 2 2 2 2
0 0 1 0 0 0
0
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
Great Blue Herons Great Egrets
Figure 1. Total reproduction results from survey inception are shown.
Total Fledges compared to total number of nests
45
40
35
30
25
20
15
10
5
0
2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
Great Blue Herons Great Egrets Total No. Nests
Figure 2. A comparison of total fledges to the total number of nests in the tree. Notice our
highest number of successful fledges occurred with relatively few nests in 2005, 2008, 2010 and
2011. Our lowest production in 2012 had the highest number of nests.
-5--6-
Figure 3. Total number of birds specific to the Roadside Rookery. Weeks 16-20 are generally considered the “busy”
time in the rookery when nestlings become apparent and eventually venture out onto the branches and are referred to as
fledglings. As they leave the nests, the numbers decline progressively until the breeding season comes to a close.Figure 4. Location of the Roadside Rookery and the associated vantage sites to view the
rookery.
-7-Figure 5. Master nest guide for 2019 season.
-8-Figure 6. Photo by Ken Butler. March 11, 2019. Prior to
leaf-out, heron delivering stick for nest building.
Figure 7. Photo by Wilt Shaw. April 10, 2019. Herons and
Egrets co-habituating in the rookery tree.
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