Success at a wonderful heronry
In 2018 LIPU-UK helped with the funding of the purchase of Canneto Boverio, in a partnership between Buchvif and LIPU; this wonderful nature reserve, small but important, was described as “A Jewel of an Oasis”. Here Professor Bogliani describes its successful development.
A new Herony in Lomellina (North-Western Italy)
A new herony has recently established itself in the Canneto Boverio natural area near Nicorvo (Pavia Province)
By Giuseppe Bogliani (translation by Alessandro Pirzio-Biroli)
In mid-June 2022 volunteers from Burchvif discovered a new herony. The herony is composed of an aggregation of Ardeidae (Heron family) nests and other colony-nesting species. It is located in the Canneto Boverio biotope, purchased years before thanks to the generous donation of Maria Grazia Boverio, as well as contributions from LIPU including an important donation from LIPU-UK. The natural area has been managed with care ever since its purchase.
The discovery of a new herony is an extraordinary event, even for this geographical area (Lomellina). Importantly, it delivers immense satisfaction to many passionate individuals and their efforts. They have volunteered a significant portion of their spare time to survey, manage and maintain the natural area since it was created in the past decades.
Findings at Canneto Boverio
Based on observations from 2022, the herony at Canetto Boverio is composed of 25 nests of Cattle Egret (Bubulcus ibis), 9 nests of Purple Heron (Ardea purpurea) , 4 nests of Little Egret (Egretta garzetta), 7 nests of Night Heron (Nycticorax nycticorax) , 3 nests of Squacco Heron (Ardeola ralloides) and 2 nests of Pygmy Cormorant (Phalacrocorax pygmeus). These were ascertained through in-site observations at the site and remote observation conducted through a drone. Five of these species are included in Attachment I of “Direttiva Uccelli”, which is Direttiva 2009/147/CE of the EU Parliament of 30th November 2009 concerning the conservation of wild birds. Specifically, the attachment states that “ … special conservation habitat measures [are required] to guarantee the reproduction and survival of these [five] species in their distribution”. Therefore, it can be argued that the Canneto Boverio natural area now has the required attributes to be transformed into a “Special Protection Zone” (ZPS, Zona di Protezione Speciale), especially since the nesting of such a number of important species becomes a regular occurrence in “Special Protection Zones”.
It is also worth noting that another species listed in Attachment I nests regularly in Canneto Boverio: Little Bittern (Ixobrychus minutus). The Little Bittern has nested in the natural area over many years, and the Bittern (Botaurus stellaris) is thought to also nest here. Canneto Boverio is extraordinary given that seven species that are listed in Attachment I nest here. Furthermore, additional species that are listed in Attachment I and nest in Canneto Boverio include: Kingfisher, (Alcedo atthis), Red-backed Shrike, (Lanius collurio), Marsh Harrier (Circus aeruginosus). This would bring the total number of species listed in Attachment I that nest in Canneto Boverio to ten, a noteworthy achievement. It should also be noted that several species that are particular to marshes and wetland areas nest in Canneto Boverio, among them Reed Warbler (Acrocephalus scirpaceus) and Marsh Warbler (Acrocephalus palustris) .
How did a new herony establish itself in a geographical area that already hosts many Ardeidae colonies?
Researchers from the University of Pavia have demonstrated that in the 1970s the Lomellina geographical region and wider rice cultivation area of the western portion of the Po Valley (i.e. provinces of Pavia, Novara, Vercelli, Turin and Milan) hosted the biggest populations of colony-nesting herons in Europe. These are species of heron that nest in groups of tens, hundreds or thousands of pairs in the same place with nests often crammed on the same trees. Studies at the time showed that this geographical area hosted tens of heronies. New conservation legislation from Piedmont and Lombardy in the 1980s resulted in almost all of these heronies being protected as reserves, natural monuments or within regional parks.
The species present in these heronies during this time were (in order of abundance): Night Heron, Little Egret, Grey Heron (Ardea cinerea) , Purple Heron and Squacco Heron. In the decades following the 1970s, the populations of these species increased and two new species added themselves to the heronies: Great White Egret (Egretta alba) and Cattle Egret. This increase and addition of new species were due to the conservation legislation protecting nest sites and the introduction of new hunting laws (until 1977 it was acceptable to hunt herons). Other non-Ardeidae species of colony-nesting waterbirds have nested (and still nest) within heronies: Spoonbill (Platalea leucorodia), Glossy Ibis (Plegadis falcinellus) , Cormorant (Phalacrocorax carbo) and most recently African Sacred Ibis (Threskiornis aethiopicus) . The African Sacred Ibis is a non-native species that escaped from captivity in the 1990s, naturalised and is now increasing in relevant numbers. Finally, in the same geographic area but nesting outside the heronies themselves can be found Bittern and Little Bittern. Unfortunately, these two species are becoming more rare.
The abundance of colony-nesting Ardeidae can therefore be explained by the widespread rice-fields which acted as surrogates for wetland areas and could function as highly suitable habitat for foraging by herons. However, from the 1990s onwards the situation changed. New rice cultivation methods became the norm. These involved periods of dry rice fields alternating with water submersion. During the dry periods, all aquatic organisms and amphibians that were characteristic of wet rice fields disappeared. Fields were also drained especially dry due to the terrain being rendered perfectly level through laser level measurements.
After a few days as a dry field, the fields would be re-submerged and remain very life-poor, although this became perfect habitat for mosquitoes which no longer had any predators or competitors. Heron populations felt the negative effects of these dry rice fields, and the numbers of two of the most abundant species at the time tumbled. Night Herons endured an immediate demographic collapse, whilst the collapse of the Little Egret was blunted (although only in the initial stages) by the species’ ability to look to rivers to forage for food. Despite the new rice cultivation methods, the Cattle Egret population instead increased. This is because the species is not particularly associated with wetlands and regularly visits fields and grasslands. There it obtains food by following agricultural vehicles that cut down vegetation or till the soil.
Night Herons perched.
Cattle Egret nests with Pygmy Cormorant in flight.
Purple Heron nest on the right and a Pygmy Cormorant.
All images above, © G Bogliani, June 2022
If one imagines that heronies hosted hundreds or thousands of nests many years ago, we recently find heronies tend to be composed of less numerous nests and overall are more scattered across Lomellina. Consequently, breeding pairs find themselves closer to new foraging areas that they have adopted as habitat, largely substituting rice fields. These include small wetlands, networks of ditches and rivers. This means that even the smallest of wetlands or marshes is ever the more vital for Ardeidae conservation, as well as the large wetland areas that are already protected. Canneto Boverio is a shining example of the former.
Graphic: Trends in nesting populations of Lombardy over the past 50 years from 1972 to 2021 of Grey Heron, Night Heron, Little Egret and Cattle Egret. From Fasola M, Cardarelli E, Pellitteri-Rosa D. 2021.
Le colonie di Ardeidi nidificanti in Lombardia 2021. Relazione conclusiva, Affidamento incarico all’Università degli studi di Pavia, Decreto n. 5717 del 19/04/2021, Identificativo Atto n. 2005, FEC 3/2021. This document, in Italian, can be read here.
The following definitions may assist the reader to understand the geographical contexts described in this article:
- “Lomellina”: a geographical and historical (albeit non-administrative) area in the Po Valley of northern Italy, located in south-western Lombardy between the Sesia, Po and Ticino rivers.
- “Po Valley”: a huge geographical and historical (albeit non-administrative) region that is a major feature of northern Italy
- “Province”: an administrative area (e.g. Pavia, Novara) that forms part of an Italian administrative region (e.g. Lombardy or Piedmont)