7.1667

11.4333

46.2667

44.1833

1972-01-01

2018-12-31

Species

Ardea cinerea

Species

Ardea purpurea

Species

Ardeola ralloides

Species

Egretta garzetta

Species

Nycticorax nycticorax

Species

Bubulcus ibis

Species

Phalacrocorax carbo

Species

Threskiornis aethiopicus

Species

Ardea alba

Species

Microcarbo pygmeus

Species

Plegadis falcinellus

Species

Platalea leucorodia

DOI

Info and download page on the LifeWatch Italy Data Portal

All the active colonies were located each year throughout the monitored area, taking advantage of the repeated occupation of traditional colony sites, and of the easily spotted groups of birds breeding in patches of seminatural vegetation within cultivated landscapes. We defined as a “colony” the whole of the breeding birds, their nests and the biotope where they are placed. In most cases, the nests in a colony were tightly clumped and clearly segregated from neighboring clumps. Groups of nests distant at least 1 km were classified as distinct colonies, while groups of nests at distance less than 1 km - so that breeding birds could interact visually or vocally - were classified as a single colony.

The nests counts were performed by expert ornithologists, during repeated visits to each colony throughout the breeding season. The counts aimed to estimate the total number of nests that were spotted at the peak of colony occupation by each species, that spanned from March for early breeders such as Ardea cinerea to June for late ones such as Ardeola ralloides. Four standardized techniques were used to estimate the total number of nests, each suited to differing habitats, colony size, and heron species. 1) Ground count of all the nests was the preferred technique, performed for easily accessible colonies, and for small (< 100 nests) and monospecific colonies. 2) Post-nesting ground count was performed for some large multi-species colonies when ground counts would produce excessive disturbance to the breeders and when foliage cover prevented precise counts during breeding. In these cases, the number of nests was estimated in four successive steps. The proportion of each species within the colony was estimated for a sample of nests observed during at least two visits during the breeding season. The total number of nests was counted during the subsequent autumn as soon as the nests become eventually visible just after the leaves have fallen. The number of nests of each species was calculated by applying the proportions recorded during breeding to the total autumn count. Eventually, this number of nests was corrected by a conversion factors (1.12 for Ardea cinerea, and 1.06 for the other species) that account for the average number of nests that disappear between the breeding period and autumn count of the step. These conversion factors had been calculated in the early years of the census as average ratio between total counts performed at the same colony during breeding and again during the subsequent autumn. 3) Aerial count of nests on low-altitude photos taken from ultralight aircrafts were used throughout the entire monitoring period for colonies in reed beds. Since 2015, nest numbers were increasingly estimated on photos taken from unmanned aerial vehicles (UAV drones) at elevations from 15 to 30 m above the nests, integrated by ground checks where possible. Surveys by drones are time-efficient and minimize disturbance to breeding birds. 4) Estimates based on the number of visible nests, and on foraging flights observed from the colony edge, were adopted in a few cases of small (< 100 nests) and completely inaccessible heronries where other techniques were inapplicable. When a precise number of nests could not be estimated, we assessed whether a species bred or not in a given colony and year (presence/absence only). The same census technique was normally adopted year after year for the same colony, and some colonies were censused by the same collaborator throughout the entire monitoring period. Training sessions were held with the collaborators, in order to assure the comparability of the results.

The dataset includes the estimated number of nests for each colony throughout the monitored area, and for each year and breeding species. We deem that all the existing colonies of the 12 waterbird species were monitored throughout the entire area, although a few cases of small groups of nests and of solitary nests of Ardea cinerea and of Nycticorax nycticorax may have been overlooked.

The dataset includes the estimated number of nests for each colony throughout the monitored area, and for each year and breeding species. We deem that all the existing colonies of the 12 waterbird species were monitored throughout the entire area, although a few cases of small groups of nests and of solitary nests of Ardea cinerea and of Nycticorax nycticorax may have been overlooked.

The nests counts were performed by expert ornithologists, during repeated visits to each colony throughout the breeding season. Four standardized techniques were used to estimate the total number of nests, each suited to differing habitats, colony size, and heron species: 1) ground count of all the nests; 2) post-nesting ground count; 3) aerial count of nests on low-altitude photos taken from ultralight aircrafts; 4) estimates based on the number of visible nests, and on foraging flights observed from the colony edge. When a precise number of nests could not be estimated, we assessed whether a species bred or not in a given colony and year (presence/absence only). The same census technique was normally adopted year after year for the same colony, and some colonies have been censused by the same collaborator throughout the entire monitoring period.