Rare rejection and incomplete responses to experimental eggs in a colonial bird

The two little egret breeding colonies were located on the farmlands of two tehsils, Rustam and Shahbaz Garhi, which are part of the Mardan district in Khyber Pakhtunkhwa Province, Pakistan. Both tehsils are located in the rural section of the Mardan district and are separated by a distance of 10 km. The tehsils are primarily occupied by farmers, and the area can be described as a picturesque mosaic of agricultural farmland and scattered meadows (Sadam et al. 2022). An excellent irrigation system permits the growth of sunflowers, fruits, nuts, vegetables, and several types of cereal grains. The study area is an agricultural area. Here, irrigation is well-established, and most people are either directly or indirectly engaged in farming or trading farm products. The study area lies north of the Buner District and Malakand protected area, northeast of Sawabi and Buner Districts, south of Nowshera District, and west of Charsadda District and the Malakand protected area. Little egret nests are simple, comprising dead branches mixed with the leaves of local trees. Little egrets lay clutches of 3–5 eggs (most often 3–4), which are oval in shape and blue-green in color (Uzun et al. 2008). The little egret colonies in both tehsils were approximately 290 m from the main towns. In total, 100 little egret nests were monitored in 2021, and 41 nests were monitored in 2022.This study focused on the egg recognition of little egrets (Egretta garzetta) and the influence of clutch size, nest stage, and parental presence on egg recognition behavior. A total of 141 nests were examined, and the results showed that egg recognition by little egrets was limited overall, with egg rejection observed only for introduced quail eggs (12.2%, n = 54), whereas waterhen (0%, n = 66) and conspecific (0%, n = 21) eggs were universally accepted. Importantly, no eggs were rejected in clutches of two or three eggs. However, rejection rates slightly increased in larger clutches, reaching 8.1% in clutches with four eggs (n = 37) and 25% in clutches with five eggs (n = 4). Moreover, nest stage and the presence of parents did not exert a significant influence on egg rejection behavior. Larger clutches with higher rejection rates may reflect a strategy to avoid nest confusion in denser colonies. However, a portion of foreign eggs may have been construed as debris instead of eggs. Our results suggest that egg recognition in this colonial bird may serve as a widespread nest identification or nest sanitation mechanism rather than as a specialized defense against brood parasitism.