Disentangling the spatial and temporal causes of decline in a bird population

Abstract

The difficulties in understanding the underlying reasons of a population decline lie in the typical short duration of field studies, the often too small size already reached by a declining population or the multitude of environmental factors that may influence population trend. In this difficult context, useful demographic tools such as integrated population models (IPM) may help disentangling the main reasons for a population decline. To understand why a hoopoe Upupa epops population has declined, we followed a three step model analysis. We built an IPM structured with respect to habitat quality (approximated by the expected availability of mole crickets, the main prey in our population) and estimated the contributions of habitat‐specific demographic rates to population variation and decline. We quantified how much each demographic rate has decreased and investigated whether habitat quality influenced this decline. We tested how much weather conditions and research activities contributed to the decrease in the different demographic rates. The decline of the hoopoe population was mainly explained by a decrease in first‐year apparent survival and a reduced number of fledglings produced, particularly in habitats of high quality. Since a majority of pairs bred in habitats of the highest quality, the decrease in the production of locally recruited yearlings in high‐quality habitat was the main driver of the population decline despite a homogeneous drop of recruitment across habitats. Overall, the explanatory variables we tested only accounted for 19% of the decrease in the population growth rate. Among these variables, the effects of spring temperature (49% of the explained variance) contributed more to population decline than spring precipitation (36%) and research activities (maternal capture delay, 15%). This study shows the power of IPMs for identifying the vital rates involved in population declines and thus paves the way for targeted conservation and management actions.

Declines in Common and Migratory Breeding Landbird Species in South Korea Over the Past Two Decades

“…Eurasian Kestrels in Northern Europe have expanded their range and had greater breeding success as spring temperature have increased (Elmhagen et al, 2015;Huchler et al, 2020). Gray Starlings and Eurasian Hoopoe forage on the ground (Joo et al, 2016;Plard et al, 2020), and warmer temperatures and increased precipitation could lead to increased prey availability in agricultural landscapes (Arlettaz et al, 2010;Plard et al, 2020). In general, precipitation during the breeding season is decreasing in Korea (Figure 1C), so any positive effects of precipitation on the probability of colonization by Eurasian Hoopoes may not be widely observed across South Korea.…”

Within‐year and among‐year variation in impacts of targeted conservation management on juvenile survival in a threatened population

“…Effective conservation of threatened populations requires identification and mitigation of key demographic constraints that limit population growth rate ( λ ), and requires thorough evaluation of management intervention efficacy (Hammers et al., 2015; Plard et al., 2020; Sarno et al., 1999; Sibly & Hone, 2002). However, identifying the causes and timing of demographic constraints, and implementing and evaluating targeted interventions, can be challenging.…”

“…For example, threatened populations are commonly thought to be food‐limited (e.g. Amar et al., 2005; Plard et al., 2020), but even when interventions aim to remedy perceived seasonal variation in natural food supply, outcomes are often evaluated solely at the annual scale (e.g. Siriwardena et al., 2007).…”

Roads reduce breeding occupancy and productivity in barn owls

“…Breeding habitat is lost as vegetation is cleared for buildings, roads, and infrastructure (Reynolds et al 2019); degradation and fragmentation of remaining habitat alters the abundance of predators and prey, potentially leading to increased nest predation and decreased food for provisioning offspring as adults spend more time foraging (Chamberlain et al 2009, Shanahan et al 2014); and light, noise, and chemical pollution can advance lay dates, alter patterns of parental care, or contaminate eggs (Kight et al 2012, Dominoni et al 2013, Kekkonen 2017). Expanding road networks and associated urbanization, thus, not only result in lower survival for individuals but can also lead to reduced reproductive output (Kociolek and Clevenger 2009), which may be the primary factor influencing many avian population declines (Newton 2004, Plard et al 2020).…”