International Journal of Molecular Zoology 2024, Vol.14, No.3, 141-153 http://animalscipublisher.com/index.php/ijmz 144 In seabirds like the Wandering Albatross (Diomedea exulans), plumage maturation is a prolonged process, with individuals taking many years to achieve their final adult plumage. This slow maturation is associated with the species' long lifespan and delayed reproductive maturity, demonstrating a different evolutionary adaptation compared to passerines and waders (Carravieri et al., 2017). 4 Delayed Plumage Maturation: Definitions and Theories 4.1 Definition of delayed plumage maturation Delayed plumage maturation (DPM) is a phenomenon observed in many bird species where juveniles, particularly males, retain subadult or non-breeding plumage for an extended period beyond their first year of life. Instead of acquiring the adult-like plumage that is often associated with reproductive maturity and social dominance, these juveniles display plumage that is typically duller and more cryptic. This retention of juvenile-like feathers can last for one or more years, depending on the species (Figure 1) (Ferreira et al., 2023). Figure 1 The evolutionary stable plumage advertisement strategy at age I (a) under different maximum survival rates (m, ranging from 0. I to 1.0) (Adopted from Lyu et al., 2015) Image caption: Figure 1 displays a heatmap analysis exploring the evolutionary stability of plumage strategies at different life stages, influenced by three variables: maximum survival rates (m), predation risk (E), and lifespan (L). The heatmap is divided into three panels corresponding to lifespans of L=2, L=3, and L=5, with each panel segmented by survival rates on the horizontal axis and predation risk on the vertical axis. The color gradient from dark blue to dark red indicates the stable value of the plumage advertisement strategy from 0 to 1. This color coding reveals the likelihood of individuals delaying maturation under varying survival rates and predation risks (deeper colors indicate earlier maturation, lighter colors suggest delayed maturation). Higher survival rates and predation risks generally favor the evolution of delayed maturation, especially in longer-lived species, demonstrating the complex interplay of these factors in evolutionary strategies (Adapted from Lyu et al., 2015) In the case of the White-bellied Shortwing (Brachypteryx leucophrys), DPM is characterized by the male juveniles maintaining a plumage similar to that of females or subadults. This cryptic plumage helps them avoid the aggression of adult males and reduces their visibility to predators. The delay in acquiring the adult plumage allows these juvenile males to survive and mature in a safer and less competitive environment (Allen et al., 2022). 4.2 Theories behind delayed plumage maturation Several theories have been proposed to explain the adaptive significance of delayed plumage maturation in birds. One prominent theory is the Crypsis Hypothesis, which suggests that retaining a juvenile-like, less conspicuous plumage helps young birds avoid predation and reduce aggression from adult conspecifics. By blending into their environment and resembling less competitive females, juvenile males can reduce the risk of aggressive encounters with dominant adult males (Ferreira et al., 2023). Another theory is the Female Mimicry Hypothesis, which posits that young males benefit from mimicking females. This mimicry can deceive adult males, allowing young males to access resources and breeding opportunities without being perceived as rivals. This strategy can help juvenile males gain experience and improve their chances of future reproductive success (Lyu et al., 2015). The Status Signaling Hypothesis suggests that delayed plumage maturation functions as an honest signal of the young male's subordinate status. This signaling reduces the likelihood of aggressive interactions with dominant
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