Short- and long-term consequences of individual and territory quality in a long-lived bird

Abstract

Site-quality is a major determinant of fitness but its effect can be confounded by individual quality, a relationship that has been little studied in large, long-lived vertebrates. The fitness effects of quality estimates depend on the assumption of co-variation between individual and territory quality and can be framed as five working hypotheses: no effect on fitness, exclusive effect of individual quality, exclusive effect of site quality, and independent or interactive effects of the two. We explored such a framework using a medium-sized raptor, the black kite Milvus migrans, as a model species. Individual and territory quality co-varied, but the strength of the relationship varied across different estimates of individual quality (age, body size, or mass residuals). Short-term production of fledglings was related to the independent effects of both individual and territory quality. However, longer-term production of recruits was related solely to territory quality. The disappearance of individual quality effects over the long-term may be caused by antagonistic selective pressures acting during different stages of the life cycle. Our results contribute to a growing appreciation of the long-term fitness-benefits of advantages experienced in early life and highlight the importance of a long-term perspective in studies assessing the effects of individual and territory quality. In our case study, prioritizing sites for conservation on the basis of territory quality may be a feasible pathway to maintain the viability of the population. However, scenarios where such a method could be inefficient have been previously reported, suggesting caution in its application. More studies are needed to understand the generality of the efficiency of priority-setting approaches based on site quality.

Effects of rearing conditions on natal dispersal processes in a long‐lived predator bird

“…In addition, this relationship underscores the fact that the prospects of being reared in good conditions are not homogeneous, and that high‐quality territories and parents produce nestlings with better body condition. This pattern is explainable by the fact that the best territories usually have more abundant and readily accessible food—the early development of chicks depends heavily on food provisioning by both parents (Rödel et al., 2009; Sergio et al., 2009)—and high‐quality individuals tend to occupy high‐quality territories (Ferrer & Bisson, 2003). …”

“…In territorial raptors, one of the most critical stages occurs when the parents expel their fledglings from their natal territory and young birds enter into a new transient nomadic phase—the dispersal period—which in Bonelli’s eagles implies long‐distance movements to dispersal areas and no territorial behavior (Cadahía et al., 2010; Real & Mañosa, 2001). Given that in our case, both territory quality and chick body condition are correlated, an explanation for our results might be that individuals with better body condition are better equipped to cope with short periods of food scarcity (Green & Cockburn, 2001; Hsu et al., 2017); alternatively, the greater concentrations of trophic resources near better territories may allow juveniles to improve hunting skills before leaving their natal territory (Sergio et al., 2009). However, the spatial and behavioral ecology of floaters (i.e., birds that have already dispersed from their natal territories) is still poorly understood, and thus, it is hard to assess how the variety of factors that come into play on nonbreeding grounds shape their survival (Barbraud et al., 2003; Bonte et al., 2012; Grande et al., 2009; Penteriani, Delgado, & Campioni, 2015).…”

“…However, our results reveal that the conditions under which chicks are reared could be relevant too as chicks reared under poor conditions will have less chances to survive until recruitment and thus to contribute to future generations. In this sense, it is worthwhile locating and targeting conservation efforts on the territories with the highest productivity rates (Sergio et al., 2009). In addition, it is vital to improve habitat and prey availability (Ferrer et al., 2014; Real, Bosch, Tinro, & Hernández‐Matías, 2016) and/or to reduce disturbances caused by human outdoor activities and/or the construction of new infrastructures in those territories where chicks are reared under poor conditions (Bosch, Real, Tintó, Zozaya, & Castell, 2010).…”

“…In addition, an understanding of the impact of rearing conditions may be highly useful in management and conservation, yet the potential consequences for future survival of offspring reared under poor environmental conditions are usually ignored. Conditions during early life vary owing to differences in parental and environmental quality (Sergio et al., 2009; Van De Pol, Bruinzeel, Heg, Van Der Jeugd, & Verhulst, 2006), and a large body of evidence exists to show that favorable rearing conditions are beneficial for individuals, particularly in short‐term effects such as increased juvenile survival (Rémy et al., 2011; Rödel et al., 2009). In this sense, Green and Cockburn (2001) and Sergio et al.…”

“…In this sense, Green and Cockburn (2001) and Sergio et al. (2009) suggest that the probability of surviving to independence is closely related to a nestling’s own quality or body condition. In fact, the onset of dispersal is generally associated with high mortality rates due to predation, stress, energy depletion, and the lack of familiarity with novel environments (Hardouin et al., 2012).…”