Recognition and utilization of egg maculation signals by twosympatric host species

Study area. This study was conducted in the Liuzhi area (26°13ʹN, 105°42ʹE), Guizhou, southwest China, from March to August during 2018–2022 and 2024.Field experiments. First, the recognition and rejection abilities of the south rock bunting and yellow-throated bunting to plain white budgerigar eggs with no markings were first examined. The method involved placing one budgerigar egg directly into a nest with a full clutch (Fig. 2a, c). After the experiment began, we checked the nests every 2–3 days and ended the experiment on the sixth day (Moksnes et al. 1991). Secondly, to test whether the two host species can use their own spot versus linear markings to identify parasitic eggs, we swapped one egg between the two species and then recorded the parent birds’ rejection of the foreign eggs (Fig. 2b, d). During the nest-checking process, if the experimental eggs were found to have disappeared from the nest or if the host birds had abandoned the nest by the end of the experiment, this was recorded as a rejection; if the foreign eggs were still in the nest and the nest was active on the sixth day, this was recorded as acceptance. Additionally, some nests were monitored with video recordings (JWD DV-58G, JWD Inc) to obtain the methods of rejection by the host.Egg-colour measure. From April to August 2024, we used an optical fiber spectrometer (AvaSpec-ULS2048×64-UA; http://avantes.cn/SensLine/56.html) to measure the reflectance spectra of the background color (300–700 nm) of 15 budgerigar eggs, 15 south rock bunting eggs, and 15 yellow-throated bunting eggs, as well as the reflectance spectra of the maculation (spots or streaks) of the two hosts’ eggs (Supporting information). Each host egg was collected from a separate nest. For the background color measurement, we took two measurements in three regions: the blunt end, the middle, and the sharp end of the egg (only the blunt and sharp end regions of the budgerigar eggs were measured). For the measurement of the maculation on the host eggs, we selected three areas with larger maculation at the blunt end of the egg and measured each area once (for a total of three measurements).Permits. The experiments comply with the current laws of China.Experimental procedures were in accordance with the Animal Research Ethics Committee of Hainan Provincial Education Centre for Ecology and Environment, Hainan Normal University (no.HNECEE-2012-004) and Experimental Animal Ethics Committee of Guizhou Normal University (no. 2021001).