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Population Trend of Colonially Nesting Heron Species in Greece

May 2024
Birds 5(2):217-239

DOI:10.3390/birds5020015

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Authors:

Savas Kazantzidis

Forest Research Institute

Theodoros Naziridis

Evangelia Katrana

Thermaikos gulf Protected Areas Management Authority

Bukas Nikolaos

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Heron colonies are dynamic components of wetlands. Therefore, their systematic monitoring is important for the management of both birds and wetlands. During the period 1988–2018, we counted breeding pairs of seven colonial breeding heron species at 65 colonies across 37 wetlands in Greece. We considered as annual variables of a population: (a) years since 1988, (b) Natura 2000 network inclusion, (c) protected area management authority overseeing, (d) wetland type (new or restored), and (e) new colonies (established after 2003). The Cattle Egret Bubulcus ibis and the Squacco Heron Ardeola ralloides had a positive breeding population trend. The Black-crowned Night Heron Nycticorax nycticorax, Little Egret Egretta garzetta, and Grey Heron Ardea cinerea had a negative trend, while the Purple Heron Ardea purpurea population was stable. The Great White Egret Ardea alba bred sporadically at only a few sites which precluded the evaluation of its population trend. The informative population variables differed among species, even of those at the same colony, which suggests trends are also affected by conditions at wintering grounds. The study highlights the need for the systematic monitoring of heron colonies and the protection of foraging/breeding areas in order to reverse the observed negative population trends.

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Citation: Kazantzidis, S.; Naziridis, T.;

Katrana, E.; Bukas, N.; Kazantzidis,

G.; Christidis, A.; Astaras, C.

Population Trend of Colonially

Nesting Heron Species in Greece.

Birds 2024,5, 217–239. https://

doi.org/10.3390/birds5020015

Academic Editor: Wenjuan Wang

Received: 15 March 2024

Revised: 9 May 2024

Accepted: 13 May 2024

Published: 15 May 2024

Licensee MDPI, Basel, Switzerland.

This article is an open access article

distributed under the terms and

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Attribution (CC BY) license (https://

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4.0/).

Article

Population Trend of Colonially Nesting Heron Species in Greece

Savas Kazantzidis 1, *, Theodoros Naziridis 2, Evangelia Katrana 2, Nikolaos Bukas 3, Georgios Kazantzidis 4,

Aristidis Christidis 5and Christos Astaras 1

1Forest Research Institute, Hellenic Agricultural Organization—DIMITRA, 57006 Vassilika, Greece;

christos.astaras@elgo.gr

2Management Unit of Protected Areas of Central Macedonia, Natural Environment and Climate Change

Agency, 57200 Lagadas, Greece; th.naziridis@necca.gov.gr (T.N.); e.katrana@necca.gov.gr (E.K.)

3Plegadis Co., R. Feraiou 6A, 45444 Ioannina, Greece; bionickbukas@hotmail.com

4Bordeaux Population Health Research Center, University of Bordeaux, 146 rue Leo Saignat CS61292,

33076 Bordeaux CEDEX, France; george_kazantzidis@outlook.com

5Fisheries Research Institute, Hellenic Agricultural Organization—DIMITRA, 64007 N. Peramos, Greece;

christar@inale.gr

*Correspondence: savkaz@elgo.gr

Simple Summary: We studied the nesting population trends of the colonially nesting heron species in

Greece from 1988 to 2018, aiming to identify drivers of these trends and thus inform colony/wetland

conservation measures. Two species (Cattle Egret and Squacco Heron) had a positive trend, while

three species (Black-crowned Night Heron, Little Egret and Grey Heron) had a negative trend. The

Purple Heron presented a stable trend. Our results suggest that: (a) The Natura 2000 network and

the operation of the protected areas Management Authorities have positively affected heron species

nesting population trend or range expansion, (b) national wetland restoration efforts have facilitated

the expansion of most heron species’ breeding range via the establishment of new colonies, and

likely to have a declining nesting population trend. The drivers behind the observed population

trends differed among species, even among those sharing the same breeding sites. This suggests

that the nesting population trends could be due to ecological changes at both the breeding and

at the wintering sites. Our results emphasize the importance of continuing wetland restoration

efforts, developing heron-friendly farming practices, and adopting a systematic nationwide survey

of colonies.

Abstract: Heron colonies are dynamic components of wetlands. Therefore, their systematic monitor-

ing is important for the management of both birds and wetlands. During the period 1988–2018, we

counted breeding pairs of seven colonial breeding heron species at 65 colonies across 37 wetlands

in Greece. We considered as annual variables of a population: (a) years since 1988, (b) Natura 2000

network inclusion, (c) protected area management authority overseeing, (d) wetland type (new or

restored), and (e) new colonies (established after 2003). The Cattle Egret Bubulcus ibis and the Squacco

Heron Ardeola ralloides had a positive breeding population trend. The Black-crowned Night Heron

Nycticorax nycticorax, Little Egret Egretta garzetta, and Grey Heron Ardea cinerea had a negative trend,

while the Purple Heron Ardea purpurea population was stable. The Great White Egret Ardea alba

bred sporadically at only a few sites which precluded the evaluation of its population trend. The

informative population variables differed among species, even of those at the same colony, which

suggests trends are also affected by conditions at wintering grounds. The study highlights the need

for the systematic monitoring of heron colonies and the protection of foraging/breeding areas in

order to reverse the observed negative population trends.

Keywords: Ardeidae; egrets; heron colonies; TRIM; wetlands; conservation

Birds 2024,5, 217–239. https://doi.org/10.3390/birds5020015 https://www.mdpi.com/journal/birds

Birds 2024,5218

1. Introduction

Nesting bird colonies are dynamic as they may change location, size, and nesting

species composition over the years. Recording and identifying potential causes of such

changes can assist in developing corrective management actions where and when neces-

sary [

]. The importance of the long-term monitoring of heron colonies for the successful

management of breeding species and their wetland habitats is recognized, which is why

many western European countries have adopted such monitoring schemes. In the UK,

for instance, monitoring—especially for the Grey Heron—has been carried out since 1928,

while in France, Spain, and Italy heron populations are systematically monitored since the

1960s or the 1970s [3–8].

All nine species of the family Ardeidae nesting in Europe breed in Greece [

]; Bittern

Botaurus stellaris, Little Bittern Ixobrychus minutus, Little Egret Egretta garzetta, the Black-

crowned Night Heron Nycticorax nycticorax, Squacco Heron Ardeola ralloides, Cattle Egret

Bubulcus ibis, Purple Heron Ardea purpurea, Grey Heron Ardea cinerea, and Great White

Egret Ardea alba), of which all but the two bittern species nest colonially. Two species are

threatened according to the Red Data Book of the threatened Animals of Greece (Purple

Heron—endangered; Great White Egret—vulnerable; [

]). The monitoring of the largest

heron colonies commenced in Greece in the 1980s [

], while nation-wide heron colony

surveys were carried out four times (2003, 2009, 2014, and 2018). Based on the mean

number of breeding pairs in the last four surveys and the European population estimates

according to IUCN Red Data list (Table A1), Greek wetlands are home to approximately

3% of the Little Egret, 2.4% of Squacco Heron, and 1.8% of Black-crowned Night Heron

European populations, indicating the international importance of Greek wetlands for heron

conservation [4,11,12].

While there are >1400 wetlands (including river deltas and their estuaries; freshwater

lakes—natural or artiﬁcial; and coastal marshes) in Greece, covering approximately 2%

of the land area, three quarters of them are small, accounting for 1% of the total wetland

area [

]. Ten of the larger ones are included in the Ramsar list of wetlands due to their inter-

national importance for bird conservation [

]. Almost all larger wetlands have one or more

heron colonies. The number of colonies and overall nest number of colonially nesting heron

species have more than doubled from 1985 to 2009 (1985: 21 colonies with 25

00–3000 ne

sts;

2003: 33 colonies and 5589 nests; 2009: 44 colonies with 6097 ne

sts) [10,11,15]

. Increases in

the number of colonies and nesting pairs were also concurrently recorded in other colonially

nesting wetland birds such as the Spoonbill Platalea leucorodia [

], Glossy ibis Plegadis

falcinellus [

], Great Cormorant Phalacrocorax carbo [

], and the Great White Pelecanus

onocrotalus and Dalmatian Pelecanus crispus pelicans [

]. The increase was probably related

to better protection following the establishment in 2003 of protected area Management

Authorities for national parks, which included most large wetlands containing the vast

majority of heron colonies [11,15].

Despite their importance for water birds, wetlands in Greece face many threats. In the

1980s and 1990s water pollution and drainage were among the main threats to wetlands.

These threats persist, even though 80% of wetlands are within protected areas (Natura

200

0 ne

twork, national parks) [

]. However, during the 21st century, some previously

drained wetlands have been restored and peoples’ attitude towards wetlands started

to change as a result of public awareness campaigns. At the same time, new threats

emerged for the heron colonies, primarily due to changes in human activities around

wetlands such as agricultural intensiﬁcation (e.g., rice cultivation) and disturbance (e.g.,

recreational activities).

The aim of the present study was to examine the available data on colonially nesting

heron species in Greece for 31 years (1988–2018) in order to estimate the population trend

of individual species, which may differ from the increasing trend observed in the overall

number of colonies and nests. Moreover, we discuss possible drivers of the observed trends,

which is a necessary ﬁrst step for designing and implementing targeted conservation

measures where and when needed.

Birds 2024,5219

2. Materials and Methods

2.1. Study Areas

The study includes data from all wetlands and wetland complexes with known heron

colonies in mainland Greece and the islands (Figure 1, Table 1). Fifty-one (79%) of these

colonies were within Natura 2000 sites and six (9%) were in new/restored wetlands. Six

colonies were situated in suburban parks (e.g., Kerkyra) or trees at the edge of a town (e.g.,

Kastoria, Aridaia), and therefore can be considered urban colonies (Table 1). There were

seven known heron colonies were not included in the analysis due to lack of data (Taka

Lake, Hotousa, Oxia island, Prasso islet, and three colonies at the Prespa Lakes, located in

northwestern Greece at the tri-state conjunction with Albania and Northern Macedonia).

Birds 2024, 5, FOR PEER REVIEW 3

2. Materials and Methods

2.1. Study Areas

The study includes data from all wetlands and wetland complexes with known heron

colonies in mainland Greece and the islands (Figure 1, Table 1). Fifty-one (79%) of these

colonies were within Natura 2000 sites and six (9%) were in new/restored wetlands. Six

colonies were situated in suburban parks (e.g., Kerkyra) or trees at the edge of a town

(e.g., Kastoria, Aridaia), and therefore can be considered urban colonies (Table 1). There

were seven known heron colonies were not included in the analysis due to lack of data

(Taka Lake, Hotousa, Oxia island, Prasso islet, and three colonies at the Prespa Lakes, lo-

cated in northwestern Greece at the tri-state conjunction with Albania and Northern Mac-

edonia).

Figure 1. Distribution of wetlands with heron colonies in Greece in 2018 (large dots = colonies

with >501 nests; medium dots = colonies with 101–500 nests; small dots = colonies with <100 nests).

Numbers refer to Table 1wetland names.

Birds 2024,5220

Table 1. List of wetlands with heron colonies included in this study, along with information on

nesting species (AC: Ardea cinerea; EG: Egretta garzetta; NN: N. nycticorax; AR: Ardeola ralloides; BI:

Bubulcus ibis; AP: Ardea purpurea; AA: Ardea alba), protection status, and type of wetland (U: urban; N:

new wetland).

a/a Wetland Name a/a Colony Name Species Nesting Protected Area

1Evros River 1 Dikaia AC, EG, NN Yes

2 N. Vissa AC, EG, NN Yes

2 Evros Delta 3 Evros Delta AP Yes

3 Ismarida Lake 4 Ismarida Lake AP Yes

4 Porto Lagos Lagoon 5 Porto Lagos AC, EG, AR, BI Yes

5Nestos River estuary 6 Keramoti AC, EG, NN Yes

7 Thassopoula (Island) EG Yes

6Kerkini Lake (artiﬁcial) 8 Kerkini AC, EG, NN, AR, AP,

BI, AA Yes

9 Limnochori AC, NN Yes

7Strymon River 10 Kouvouklio AC No

11 Strymon River EG, AA No

8Volvi–Koronia Lakes

(partially, Koronia Lake, restored)

12 Big plane tree AC Yes

13 Small plane tree AC Yes

14 Apollonia forest main AC Yes

15 Apollonia forest east EG Yes

16 Koronia west EG, NN, AR, AP, AA Yes

17 Koronia east AC Yes

Axios–Aliakmon–Gallikos Deltas

(partially, N. Agathoupolis Marsh,

restored, N)

18 Axios Delta main

AC, EG, NN, AR, BI, AA

Yes

19 Axios danio AP Yes

20 Gallikos River old EG, AR Yes

21 Gallikos Riner new AC Yes

22 N. Agathoupolis AP Yes

10 Sani marsh (restored, N) 23 Sani AC, EG, NN, AP Yes

11 Aliakmon River 24 Kouloura AC, EG No

12 Almopaios River 25 Aridaia (U) AC Yes

26 Krania Almopias AC Yes

13 Petron Lake 27 Petron AC, EG, NN, AR, AP Yes

14 Chimaditida Lake 28 Chimaditida AP Yes

15 Kastoria Lake 29 Kastoria Lake (U) AC, EG, NN Yes

30 Kastoria town (U) NN Yes

16 Grevenitis River 31 Grevenitis AC No

17 Poliﬁtou Lake (partially artiﬁcial)

32 Rimnio AC No

33 Velvendos AC, EG No

34 Velvendos cormo AC No

35 Ilarion Dam EG No

18 Elassona River 36 Elassona AC Yes

19 Tyrnavos Lake-pond (artiﬁcial) 37 Mati Tyrnavos AC No

Birds 2024,5221

Table 1. Cont.

a/a Wetland Name a/a Colony Name Species Nesting Protected Area

20 Neochoritis River 38 Neochoritis AC, EG Yes

21 Trikala Marsh (artiﬁcial, N) 39 Trikala EG, NN, AR No

22 Karla Lake (restored, N)

40 Glafki AC, EG, NN, AR Yes

41 Galini (U) AC Yes

42 Platycampos (U) AC Yes

43 Karla Lake EG, NN, AR, AP, AA Yes

44 Kanalia AC, NN Yes

23 Spercheios Delta 45 Spercheios EG, NN Yes

24 Pamvotis Lake 46 Ioannina AC Yes

25 Kalamas River estuary

47 Sagiada AC, EG, NN, AR Yes

48 Thesprotia AC, AR Yes

49 Prassoudi islet (Island) EG, AR, BI Yes

26 Kerkyra Marsh (Corfu Island) 50 Kerkyra (Corfu), (U) AC No

51 Caparelli EG No

27 Acheron River estuary 52 Acheron AC, EG, NN, AR, AP Yes

28 Kalodiki Lake 53 Kalodiki AC, EG, NN, AR Yes

29 Amvrakikos wetland

54 Rodia marsh EG, NN, AR, AP Yes

55 Psathotopi AP Yes

56 Korakonisia (Island) EG, BI Yes

57 Gaidouronisi (Island) EG Yes

30 Amvrakia Lake 58 Amvrakia EG, NN, AR, AP, BI Yes

31 Limnopoula Lake 59 Limnopoula AC Yes

32 Smokovo River 60 Smokovo AC No

33 Messolonghi–Acheloos Delta 61 Messolonghi EG, NN, AR, AP Yes

34 Prokopos Marsh 62 Prokopos AP Yes

35 Stymfalia Lake 63 Stymfalia AP Yes

36 Evrotas River estuary 64 Evrotas AC, EG, AR Yes

37 Gadouras Dam Lake (N) 65 Rhodos (Island) EG No

Management actions within the Natura 2000 sites commenced only after the establish-

ment of the ﬁrst protected area Management Authorities in 2003. Ten of those Management

Authorities had existing heron colonies within their jurisdictions. In effect, heron colony

conservation commenced from that point on.

Using mostly European Union funds, several efforts to restore degraded or drained

wetland have taken place [

]. The ﬁrst and largest restored wetland was Karla Lake

(c. 3800 ha) in Thessaly, central Greece, in 2000, followed by many smaller wetlands [

–

]

(Table 1; Figure 1). In addition, at least 54 reservoirs were built in Greece from 2003 to

2012 [

], either for irrigation purposes or to restore previously drained wetlands. In

some of these new or restored wetlands, heron and/or Great Cormorant colonies were

established (e.g., at the restored Sani and N. Agathoupolis marshes and Koronia Lake in

northern Greece, and the new pond built in Trikala, central Greece; Table 1).

The species considered in this study are all the colonially nesting heron species breed-

ing in Greece; Little Egret, Black-crowned Night Heron, Squacco Heron, Cattle Egret, Purple

Heron, Grey Heron, and Great White Egret. Five species were not included either because

Birds 2024,5222

they are not colonial breeders (Bittern and Little Bittern) or because they are only sporad-

ically reported and not known to breed in Greece (Western Reef Heron Egretta gularis in

2008 [

]; Black Heron Egretta ardesiaca in 2012 [

], Green-backed Heron Butorides striatus

in 2019—see F. Samaritakis, pers. comm.). We did not include other species often breeding

within heron colonies in this study, such as the Spoonbill Platalea leucorodia, Glossy Ibis

Plegadis falcinellus, Pygmy Cormorant Microcarbo pygmaeus, Great Cormorant Phalacrocorax

carbo, and Crested Grebes Podiceps cristatus.

The data used for this study are from (a) four national surveys of heron colonies,

nesting species and their populations (number of nests) conducted in 2003, 2009, 2014,

and 2018; (b) surveys at most (but not all) colonies in 1988, 1989, 1990, and 2015; and

Delta, Kerkini Lake, Axios Delta, Koronia—Volvi Lakes, and Kalamas Delta; Table 1).

2.2. Inventory of Colonies

All possible areas that can host a heron colony were visited during the four national

colony surveys, utilizing information collected from local birdwatchers [

]. During the

ﬁeld visit, the coordinates, nest tree species and predominant tree species, number of breed-

ing pairs per species, and possible anthropogenic threats were recorded for each colony.

2.3. Nest Count

The number of each species’ nests was recorded during the peak of the chick rearing

period (late May–early June, [

]). At four colonies (at Axios Delta and the Kerkini and

Koronia Lakes), a second visit was carried out (until mid-June) speciﬁcally for counting

Squacco Heron nests, as the species starts nesting later compared to other heron species.

Nests were counted from a distance either from the ground or from boat, outside the colony,

using binoculars and/or telescopes. In the case of three colonies (one colony at Amvrakikos

and two colonies at the Volvi and Koronia Lakes), which were either inaccessible on foot

or by boat or the nests were located within thick foliage or reedbed and not visible, we

estimated the number of nests by tallying the departing birds of each species for the feeding

grounds for one hour after dawn, assuming that two birds corresponded to one nest [

The nests of Grey Heron colonies were counted in April, as this species starts breeding

as early as February. Given the nesting trees typically used by this species, a May–June

count of nests would have been problematic due to thick foliage. For this reason, in some

colonies, we counted the nests by entering the colony in the morning (6–9 a.m.) either on

foot (Axios Delta) or by boat (Kerkini, Kastoria Lakes) and using binoculars.

2.4. Trend Analysis

To estimate the nest population trend of a species across the study period while

taking into consideration the years with no survey data, we used the Trends and Indices

for Monitoring Data (TRIM) software vers. 2.1.1 [

], which was developed speciﬁcally

for analyzing data from incomplete wildlife surveys using log linear Poisson regression

models [

]. TRIM is widely used in estimating breeding bird population trends [

]. In

addition to the mandatory “Time” variable, which refers to the years elapsed since the ﬁrst

survey year (1988), we considered four additional colony parameters which could explain

the observed changes in a species’ nests in monitored colonies:

(a) “Natura 2000”, which indicates if the colony was situated within the Natura 2

000 ne

twork

of protected areas.

(b)

“Management Authority”, which indicates if the colony was situated within the

jurisdiction of a protected area management authority (as of 2003, the year these

authorities were established in Greece).

(c)

“New/restored wetland”, which indicates if the colony was in a wetland that was

either established (new) or restored after 2003.

(d) “New colony”, which indicates if the heron colony was a colony established after 2003.

Birds 2024,5223

Data from all 1988–2018 surveys were combined. Colonies with three or less counts

were excluded from the analysis. Missing counts (i.e., imputed values) ranged from 12%

for the Cattle Egret to 53% for the Grey Heron. The Akaike Information Criterion (AIC)

was used for model selection [

]. In order to have an optimal set of informative variables

while managing for model complexity, we ﬁrst ran univariate models of each parameter

against the baseline model (i.e., model that includes as covariates only time—i.e., elapsed

years since 1988—and site). Only informative variables (i.e., with univariate models having

<AIC than the baseline model) were included in multivariate combinations. Population

trends (i.e., slopes) were computed along with associated conﬁdence intervals (CI) at the

5% signiﬁcance level and interpreted using the following classiﬁcation [28].

(a)

Strong increase: more than 5%/year (lower CI limit > 0.05).

(b)

Moderate increase: less than 5%/year (lower CI limit > 0.0).

(c)

Stable: no signiﬁcant increase or decline (−0.05 < lower < 0.0 < upper < 0.05).

(d)

Moderate decrease: less than −5%/year (upper CI limit < 0.0).

(e)

Strong decrease: more than −5%/year (upper CI limit < 0.05).

(f)

Uncertain, any other case.

3. Results

In total, 65 heron colonies in 37 wetlands were surveyed at least once during the study

period (Figure 1; Table 1). Of the four national surveys (2003, 2009, 2014, 2018), the highest

number of active colonies was in 2009 (n = 44), when the highest number of heron nests

(all species) was also recorded (6097). In 2014, the total nests were 5903 in 43 colonies,

while 5589 nests in 33 colonies and 4853 nests in 32 colonies were recorded in 2003 and

2018, respectively.

Herons often formed mixed colonies. However, Grey and Purple Herons, Little Egrets,

and, rarely, Black-crowned Night Herons formed mono-speciﬁc colonies as well. Of the

34 (52%) monospeciﬁc colonies, most (n = 19) were Grey Heron colonies. The rest were

colonies of Purple Herons (n = 8), Little Egrets (n = 6), and Black-crowned Night Herons

(n = 1) (Table 1).

The nest population trend of the study species differed (Table 2). The Cattle Egret

and the Squacco Heron were the species with an increasing trend (strong and moder-

ate, respectively), while three species showed a decreasing trend (Black-crowned Night

Hero

n—stron

g decrease, Grey Heron and Little Egret—moderate decrease). The Purple

Heron population appeared to be stable. The Great White Egret nested sporadically, with

small number of nests and at a few sites only, so its population trend could not be evaluated

(Table 2).

Table 2. Herons’ nesting population trend (regression model taking into consideration the coefﬁcient

“Time”) and their colonies’ characteristics in Greece during the study period, 1988–2018.

Species

Nesting Population

Trend—Slope β(se) and

p-Value

Mean Number of

Nests/Colony ±SD

(Min.–Max.)

Number of

Colonies

(Wetlands)

Colonies in

Protected Areas

Little Egret Moderate decrease

−0.014 (0.001) p< 0.001 226.6 ±125.2

(1–902) 33 (25) 27

Black-crowned Night Heron Strong decrease

−0.099 (0.008) p< 0.001 285.8 ±297.4

(2–980) 22 (17) 21

Squacco Heron Moderate increase

0.01 (0.014) p< 0.001 78.4 ±118.4

(1–501) 17 (17) 16

Cattle Egret Strong increase

0.159 (0.016) p< 0.001 26.1 ±38.5

(1–113) 6 (6) 6

Birds 2024,5224

Table 2. Cont.

Species

Nesting Population

Trend—Slope β(se) and

p-Value

Mean Number of

Nests/Colony ±SD

(Min.–Max.)

Number of

Colonies

(Wetlands)

Colonies in

Protected Areas

Purple Heron Stable

−0.003 (0.005) p= 0.49 8.0 ±5.5

(1–25) 17 (14) 14

Grey Heron Moderate decrease

0.058 (0.005) p< 0.01 95.9 ±87.0

(1–320) 39 (26) 30

Great White Egret Not evaluated 4.7 ±10.4(1–39) 5 (5) 4

The species with the largest average number of nests per colony were the Black-

crowned Night Heron (285.8

297.4) and the Little Egret (226.6

125.2). Conversely, the

Purple Heron had on average the lowest number of nests per colony (8.0 ±5.5; Table 2).

3.1. Little Egret (Egretta garzetta)

In 2018, the Little Egret was the most numerous heron species in terms of total nests

(2083) and the second most widespread in terms of number of colonies (n = 16). Most (91.2%)

of the nests were located in six colonies in northern and western Greece (Kerkini Lake,

Axios Delta, Porto Lagos, Keramoti, Prassoudi, and Rodia in the Amvrakikos wetland,

Figure 1; Table 1). The highest number of nests was recorded in 2009 (n = 2506) with

breeding taking place in 19 colonies. The moderate population decrease observed (Figure 2;

Table 2) was characterized by a concurrent decrease in the mean number of nests per

colony and an increase in the number of colonies (Figure 3). Fourteen new colonies were

established after 2003, of which most (n = 9) were within protected areas (six in areas

actively protected by the respective Management Authority). At least four of these new

colonies (including three of those actively protected) were later abandoned.

Birds 2024, 5, FOR PEER REVIEW 8

The species with the largest average number of nests per colony were the Black-

crowned Night Heron (285.8 ± 297.4) and the Lile Egret (226.6 ± 125.2). Conversely, the

Purple Heron had on average the lowest number of nests per colony (8.0 ± 5.5; Table 2).

3.1. Lile Egret (Egrea garzea)

In 2018, the Lile Egret was the most numerous heron species in terms of total nests

(2083) and the second most widespread in terms of number of colonies (n = 16). Most

(91.2%) of the nests were located in six colonies in northern and western Greece (Kerkini

Lake, Axios Delta, Porto Lagos, Keramoti, Prassoudi, and Rodia in the Amvrakikos wet-

land, Figure 1; Table 1). The highest number of nests was recorded in 2009 (n = 2506) with

breeding taking place in 19 colonies. The moderate population decrease observed (Figure

2; Table 2) was characterized by a concurrent decrease in the mean number of nests per

colony and an increase in the number of colonies (Figure 3). Fourteen new colonies were

established after 2003, of which most (n = 9) were within protected areas (six in areas ac-

tively protected by the respective Management Authority). At least four of these new col-

onies (including three of those actively protected) were later abandoned.

Figure 2. Nest population trend of the Lile Egret Egrea garzea in the 1988–2018 period in Greece

(moderate decrease). The red dots indicate the percentage of nests in a given year relative to the

1988 nest population, as estimated from the ﬁed model values of the best model (% of imputed

values: 48). Dashed line marks the estimated percent of nests in 1988.

Figure 3. Changes in the number of Lile Egret Egrea garzea colonies (F = 25.54, df = 6, R2adj = 0.778,

p = 0.002) and the mean number of nests per colony (F = 17.64, df = 6, R2adj = 0.704, p = 0.006) in the

1988–2018 period in Greece.

Figure 2. Nest population trend of the Little Egret Egretta garzetta in the 1988–2018 period in Greece

(moderate decrease). The red dots indicate the percentage of nests in a given year relative to the

88 n

est population, as estimated from the ﬁtted model values of the best model (% of imputed

values: 48). Dashed line marks the estimated percent of nests in 1988.

Birds 2024,5225