The research team, led by observers who monitored the wetland over three consecutive breeding seasons from 2020 to 2022, applied a statistical technique known as binary logistic regression to answer a deceptively simple question: what combination of water depth and vegetation type best predicts where spoonbills will be found? The method, widely used in habitat modeling for presence and absence data, transforms the dependent variable into a logit and applies maximum likelihood estimation, producing coefficients that can be translated directly into probabilities of occurrence across a landscape.

The results were striking. The model achieved an area under the receiver operating characteristic curve of 0.993 ± 0.008, a value approaching the theoretical maximum of 1.0 for a perfect fit. In practical terms, the ROC curve, which graphs the trade-off between false positives and false negatives, showed that the model could almost perfectly discriminate between locations where spoonbills were present and those where they were absent. The overall classification accuracy reached 98.1 percent at a probability cut-off value of 0.64, with 22 of 22 absence points correctly classified and 30 of 31 presence points identified correctly.

Gandoman Wetland sits at an average elevation of 2220 meters above sea level in the Aqbolaq watershed, on the eastern flank of the Kalar highlands, and lies downstream of the Choghakhor International Wetland, a site designated under the Ramsar Convention. Water flowing out of Choghakhor feeds into Gandoman, linking the two systems ecologically. This connectivity matters: the study suggests Gandoman functions as a corridor habitat for spoonbills and many other birds, which occupy the wetland during the breeding season and depart as winter approaches.

Fieldwork was intensive and systematic. From late April to mid-July, once a week for three years, observers recorded feeding, foraging, and nesting locations using GPS, monitored the birds with a Swarovski 20×60 monocular telescope, Steiner 8×30 binoculars, and a Canon 50× spotting scope, and measured water depth at both nest sites and foraging grounds. Wherever evidence of spoonbill activity was found, the location was logged as a presence point; areas monitored for three years without any spoonbill observation were marked as non-presence points, a conservative approach reflecting the fact that absence data cannot be verified with the same certainty as presence.

The regression coefficients revealed a clear pattern with direct management implications. Water depth emerged as a significant predictor, with a coefficient of -0.168 and a statistically significant p-value of 0.016, meaning that as depth increased, the probability of spoonbill presence for feeding decreased. The birds fed almost exclusively in water shallower than 40 centimeters, consistent with previous findings that the species can forage only in water no deeper than this threshold. Their long legs, necks, and bills allow them to exploit deeper water than smaller waders, but only up to a point.

Vegetation preferences differed sharply between activities. For foraging, the analysis pointed to areas dominated by Carex-Juncus associations, sedges and rushes that typically grow in sparse stands with open water between them. For nesting, the birds favored denser combinations of Cladium-Cyperus and Blysmus-Phragmites species, tall reeds and sedges that provide concealment. The Exp(B) values from the model quantified these associations, indicating that Blysmus-Phragmites, Cladium-Cyperus, and Juncus communities increased the odds of presence for feeding, while Carex-Juncus and Phragmites-Cyperus-Cladium combinations were associated with nesting sites.

The behavioral logic behind this split is straightforward but elegant. Nests built among dense reeds gain camouflage and physical protection, shielding eggs and chicks from predators that threaten the species on land or in shallow water. Foraging, by contrast, requires visibility and access: high, dense vegetation can limit a waterbird’s ability to detect prey and move through the wetland, so spoonbills selected areas with sparse vegetation where their sweeping bill-stroke could work efficiently. This balance between predation risk and foraging access is a recurring theme in waterbird ecology, and the study quantifies it precisely for one species at one site.

The findings arrive against a sobering global backdrop. Wetlands cover less than 2 percent of Earth’s continental surface and are being lost at roughly three times the rate of natural forests, driven by climate change, urbanization, drainage, wastewater discharge, and land-use conversion. Because waterbirds sit near the top of aquatic food chains and depend on wetlands for feeding, sheltering, and breeding, they serve as sensitive indicators of ecosystem condition. The Eurasian Spoonbill itself, listed as Least Concern globally by the IUCN Red List, is regarded as a flagship, umbrella, and indicator species, meaning its protection confers benefits on a broader community of wetland organisms.

The study also documents a local success story. Restoration measures in recent years, including the construction of an earthen dam at the eastern exit of the wetland, have increased water depth in the northern and central portions and expanded the extent of reed growth. The authors suggest these changes should support a growing spoonbill breeding population in the coming years, although agricultural development and the wetland’s proximity to a nearby city remain potential threats. The site has already been designated a prohibited hunting area by Iran’s Environmental Protection Organization, and the researchers argue that continued monitoring could justify its recognition as an Important Bird Area.

Perhaps the most broadly applicable conclusion is that no single wetland can meet all the requirements of a diverse waterbird community. Different species need different water depths, vegetation structures, and levels of isolation from human disturbance. From a landscape perspective, surrounding wetlands influence both the number of waterfowl species a site can support and their reproductive performance. The authors therefore advocate developing and maintaining multiple complementary wetlands within an ecosystem, a strategy that the Gandoman-Choghakhor pair, linked by water and by the movements of the birds themselves, already exemplifies. For a species that arrives each March, nests among the reeds, and feeds in the shallows before departing in autumn, the future of such interconnected wetland mosaics may determine whether the spoonbill’s spatula bill continues to stir Iranian waters each spring.

Subject of Research: Habitat preference modeling for nesting and foraging Eurasian Spoonbills in the Gandoman Wetland, Iran

Article Title: Habitat preference for nesting and foraging of Eurasian Spoonbill ( Platalea leucorodia ) in breeding season

Article References: Habitat preference for nesting and foraging of Eurasian Spoonbill ( Platalea leucorodia ) in breeding season. (n.d.). https://doi.org/10.3897/saddi.30.161299

Image Credits: AI Generated

DOI: 10.3897/saddi.30.161299

Keywords: Eurasian Spoonbill, Platalea leucorodia, Gandoman Wetland, habitat suitability modeling, binary logistic regression, water depth, wetland vegetation, breeding season, waterbird conservation, Iran, ROC curve, wetland management