The interacting effects of forestry and climate change on the demography of a group-living bird population

Abstract

Anthropogenic degradation of natural habitats is a global driver of wildlife population declines. Local population responses to such environmental perturbations are generally well understood, but in socially structured populations, interactions between environmental and social factors may influence population responses. Thus, understanding how habitat degradation affects the dynamics of these populations requires simultaneous consideration of social and environmental mechanisms underlying demographic responses. Here we investigated the effect of habitat degradation through commercial forestry on spatiotemporal dynamics of a group-living bird, the Siberian jay, Perisoreus infaustus, in boreal forests of northern Sweden. We assessed the interacting effects of forestry, climate and population density on stage-specific, seasonal life-history rates and population dynamics, using long-term, individual-based demographic data from 70 territories in natural and managed forests. Stage-specific survival and reproductive rates, and consequently population growth, were lower in managed forests than in natural forests. Population growth was most sensitive to breeder survival and was more sensitive to early dispersing juveniles than those delaying dispersal. Forestry decreased population growth in managed forests by reducing reproductive success and breeder survival. Increased snow depth improved winter survival, and warmer spring temperatures enhanced reproductive success, particularly in natural forests. Population growth was stable in natural forests but it was declining in managed forests, and this difference accelerated under forecasted climate scenarios. Thus, climatic change could exacerbate the rate of forestry-induced population decline through reduced snow cover in our study species, and in other species with similar life-history characteristics and habitat requirements.

Hot droughts compromise interannual survival across all group sizes in a cooperatively breeding bird

“…Together these processes likely contribute to the overall trend for population decline in below‐average rainfall years in this species (Wiley, 2017). Negative effects of adverse climate conditions on the interannual survival of breeding adults are particularly concerning because interannual survival rates of breeding adults (compared to non‐breeding adult helpers) have the greatest impact on population growth rates in this species (Wiley, 2017), and hence the probability of population persistence through time (Layton‐Matthews et al ., 2018).…”

“…We expected negative effects of high temperatures, and positive effects of high rainfall and larger group sizes, on (1) ∆M b in juveniles and in breeding adults, (2) survival of juvenile birds from nutritional independence at 90 days of age to recruitment into the adult population at 1 year of age and (3) survival of breeding adults from one breeding season to the next. Analyses do not include subordinate adults because subordinate adults (both sexes) often disperse (Ridley et al ., 2008; Raihani et al ., 2010) and dispersal is easily confounded with mortality (Layton‐Matthews, Ozgul, and Griesser, 2018). We further predicted that larger group sizes would buffer against climatic effects due to load‐lightening allowing individuals to invest more in self‐directed behaviours during periods of harsh weather.…”

Remotely sensed forest understory density and nest predator occurrence interact to predict suitable breeding habitat and the occurrence of a resident boreal bird species

“…Open forests, in contrast, are associated with a warmer microclimate. This leads to earlier snowmelt with an increased access to food in spring and reduced incubation costs, with a subsequently higher breeding success (Layton‐Matthews, Ozgul, & Griesser, ). Our results suggest that forest understory density within ca.…”

Forest management affects seasonal source-sink dynamics in a territorial, group-living bird

“…Following Layton-Matthews et al (2018), we parameterised two periodic, stage-structured, population matrices (K summer , K winter ), which describe demographic processes from summer to winter and from winter to summer, for natural and managed forest (Caswell and Trevisan 1994;Caswell 2001). The winter matrix (right, K winter ) projected the population from the two summer stages (sn and sb) onto four winter stages (rj, dj, wn and wb).…”

“…This increases adult predation risk by visually hunting hawks and owls, and also nest predation risk by other corvids (Griesser et al 2006(Griesser et al , 2007(Griesser et al , 2017. Consequently, forestry management increases mortality and reproductive failure in Siberian jays (Griesser et al 2007;Layton-Matthews et al 2018). By modelling the dynamics of a Siberian jay metapopulation (70 territories), located in natural and managed forest, we quantified the effects of forestry on seasonal metapopulation dynamics and metapopulation stability.…”