In wetland ecosystems, birds play a crucial role in nutrient cycling through various activities such as excrement deposition, sediment disturbance during foraging, and utilization of mud and vegetation for nesting. Particularly noteworthy are species exhibiting colonial breeding or high sociability, as they can significantly influence waterbody communities and act as ecosystem engineers in these habitats. Flamingos (Phoenicopteridae) possess all these characteristics, making them potential ecosystem engineers. In this study, we aim to test the hypothesis that Chilean Flamingos (Phoenicopterus chilensis) exert such effects on an important non-breeding wetland. Moreover, we seek to elucidate the underlying reasons for these effects and their relationship with flock size and foraging behavior. To accomplish this, we conducted a year-long study on the flock of Chilean Flamingos at Lagoa do Peixe National Park in southern Brazil. We collected environmental and behavioral data, including nitrogen, phosphorus, and dissolved oxygen levels, water turbidity, salinity, and temperature, from areas both with and without flamingos. Our findings suggest a significant role of Chilean Flamingos in maintaining the nutrient cycle within wetland ecosystems. This is attributed not only to the high levels of guano deposition, but also to the bioturbation caused by their foraging behaviors. Furthermore, we observed a significant correlation between flock size, the mean duration of foraging behaviors, and the magnitude of these effects. This study points the likely effects of flamingos to wetlands ecosystems, emphasizing the intricate interplay between these birds and their habitats and highlights the importance of conserving both the species and their ecosystems.

Between October 2021 and September 2022, a series of monthly field procedures and data collection endeavors were carried out in the Barra and central regions of Lagoa do Peixe National Park, covering an approximate area of 1500 ha. The Chilean flamingo flocks were located using an active search strategy during each field excursion, in collaboration with park personnel. Upon locating a flock, behavioral observations were conducted utilizing the Focal Animal method. The method involved deliberately selecting an individual for continuous observation over a period of five minutes. To mitigate sampling bias, we endeavored to select foraging animals that were at a considerable distance from previously sampled individuals whenever feasible. Detailed notes were made regarding each behavior exhibited by the focal individual, including the duration of each behavior, with particular emphasis on foraging behaviors. Behaviors were also classified into two types: events and states. Events are brief, often instantaneous behaviors that occur momentarily, while states are behaviors that last for a significant duration and often involve more conspicuous or continuous movements.

Observations were facilitated using binoculars, supplemented using a professional photographic camera when feasible. Adherence to a pre-established habituation period of 30 minutes before the commencement of observations, along with maintaining a minimum distance of 200 m from the observed flock, served to mitigate potential observer biases that could otherwise influence data collection. To mitigate single observer bias, a subset of behavioral videos was analyzed using the software BORIS; we then compared the measurements between field observations and video analysis, to assess the reliability of the data. In addition, the total number of Chilean flamingos within the observed flock was recorded during the study.

Following behavioral observation of each foraging Chilean flamingo flock within a 500-meter radius, we proceeded to collect samples of 100 mL of water from the lagoon (called F₀ samples). The samples were taken directly at the points where the foraging flamingos were previously observed, and the 500-meter radius ensured that we did not pseudo-replicate the same areas twice, avoiding any sampling bias in further statistical analysis. This sampling process strictly adhered to recommended methodologies for collection and preservation outlined by the South America Flamingo Census. Concurrently, a control sample (C₀) was obtained from a location at least 2 km distant from the original sampling site, in a suitable foraging area of these animals but devoid of any flamingo presence. Subsequently, on the same day, both the initial sampling point and its corresponding control point were revisited and resampled after an interval of three hours, following the departure of flamingos from the initial area (called F₃₊ and C₃₊, respectively). This methodology ensured the acquisition of paired samples, at two distinct points in time and space, with both temporal and spatial controls, helping us determine whether changes in the lagoon were related to the presence of flamingos or caused by external factors. Sampling sites where flamingos remained in the initial area after the three-hour period, or control points where flamingos were present after the same duration, were excluded from the analysis. The primary objective of this sampling regimen is to enable comparative analysis and measurement of nutrient levels, verifying whether flamingos indeed have effects on the areas, and if these effects persist over time.

Each water sample underwent analysis to determine the concentrations of dissolved oxygen (O₂), total nitrogen (NO₃^- and NO₂^-), and phosphorus (PO₄). Analysis was conducted employing a photocolorimetry technique, wherein specific reagents were introduced into the solution, forming chromogenic reactions with the target molecules. This results in characteristic color changes directly proportional to the concentration of the respective molecules. The intensity of coloration was subsequently compared against a known quantity standard curve, facilitating the precise quantification of the targeted molecules within the water samples obtained from the lagoon, in mg/L. A similar process was utilized to measured water turbidity, where the water sample was homogenized and image analysis was employed to determine the level of turbidity in the sample, expressed in NTU (Nephelometric turbidity units), based on a known standard curve. To ensure the integrity of results, analyses were promptly executed following sample collection, within the shortest possible time frame. In addition to nutrient analysis, on-site measurements of salinity (expressed in parts per thousand) and water temperature (in degrees Celsius) were conducted utilizing a calibrated multiparameter meter by Akso.