![]() Here we use protein fingerprinting to assess the validity of the MED method. The MED method has been tested in Finnish and Scottish common goldeneye Bucephala clangula populations but the results have been contradicting. In conclusion, our novel approach based on machine learning provided important insights on how signallers broadcast their specific signature cues to enhance their recognisability.Įadie (1989) developed a method based on variation between females in egg length, width and weight to detect conspecific brood parasitism in the field: using these three egg measures, Euclidean distance between all pairs of eggs within a clutch is calculated, and if maximum Euclidean distance (MED) between any two eggs exceeds a threshold value the nest is considered parasitized. Thus, repetition of egg design within a clutch would reinforce signals and would help females to create an internal template for true recognition of their own eggs. ![]() Algorithm classification performance improved by each extra training egg added to the model. Most important variables for classification were those with the highest intraclutch correlation, demonstrating that individual recognition traits are repeatable. Therefore, egg phenotypes should be assessed in their full complexity, including colour, patterning, shape and size. Simplified models with fewer explanatory variables (10 or 15) showed lesser classification ability than full models, suggesting that birds may use multiple traits for egg recognition. This finding supports the hypothesis that eggs have visual identity signals in their phenotypes. The best model with all 27 explanatory variables assigned correctly 53.3% (CI = 42.6-63.7%) of eggs of the test-set, greatly exceeding the probability to classify the eggs by chance (1/92, 1.1%). Then, we used these variables in a supervised machine learning algorithm for multi-class egg classification, where each egg was classified to the best matched clutch out of 92 studied clutches. Using SpotEgg, we characterized the eggs in 27 variables of colour, spottiness, shape and size from calibrated digital images. We used 92 clutches (460 eggs) of the Eurasian coot Fulica atra to test whether eggs could be correctly classified into their corresponding clutches based only on their external appearance. Most studies have put their focus on individual abilities to carry out these behavioural tasks, while less attention has been paid to the egg and how its signals may evolve to enhance its identification. However, the mechanisms of egg recognition and discrimination are poorly understood. Our results confirm that Eadie's method is reliable enough to identify parasitized clutches in Common Goldeneyes.īrood parasitized and/or colonial birds use egg features as visual identity signals, which allow parents to recognize their own eggs and avoid paying fitness costs of misdirecting their care to others' offspring. Further analyses suggested that MED>3.0 can be used as a conservative and reliable criterion to identify parasitized clutches. The mean MED of naturally parasitized clutches (4.83) was higher than that of nonparasitized clutches (2.12). Test clutches that included three eggs from each of three different females (9 eggs in all) had a mean MED of 4.51. Test clutches of 3 eggs that included one egg from each of three different females had a higher MED (2.80) than 3-egg clutches that included eggs from one female only (2.05), proving that there is statistically significant variation in egg morphology between females. Euclidean distance between the two most dissimilar eggs (maximum Euclidean distance, MED) was used as the criterion to identify parasitized clutches. Using these measures, Euclidean distance for each pair of eggs within a clutch was calculated. Eadie's method is based on z-score standardized measures of length, width, and weight of eggs. We used data from three Common Goldeneye Bucephala clangula populations in Finland to study if the variation between females in egg morphology, as measured using a method developed by Eadie (1989), can be used to identify parasitized clutches.
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