Habitat quality affects stress responses and survival in a bird wintering under extremely low ambient temperatures

Abstract

Animals normally respond to stressful environmental stimuli by releasing glucocorticoid hormones. We investigated whether baseline corticosterone (CORT), handling-induced corticosterone concentration(s), and body condition indices of members of willow tit (Poecile montanus) groups differed while wintering in old growth forests and managed young forests in mild weather conditions and during cold spells. Willow tits spend the winter season in non-kin groups in which dominant individuals typically claim their priority to access resources, while subordinate individuals may experience greater levels of stress and higher mortality, especially during cold spells. We captured birds to measure baseline CORT and levels of handling-induced CORT secretion after 20 min of capture. Willow tits in the young forests had higher baseline CORT and a smaller increase in CORT in response to capture than individuals in the old forests. Baseline CORT was higher in females and juvenile birds compared to adult males, whereas handling-induced CORT secretion did not differ between birds of different ages. During cold spells, baseline CORT of willow tits increased and handling-induced CORT secretion decreased, especially in birds in young forests. Willow tits' survival was higher in the old forests, with dominant individuals surviving better than subordinates. Our results show that changes in CORT secretion reflect responses to habitat quality and climate harshness, indicating young managed coniferous forests as a suboptimal habitat for the willow tit.

Attacks of songbirds in mixed‐species flocks by Eurasian Sparrowhawks: strategies of predators and potential prey

“…Attacks on members of mixed‐species flocks of birds by Eurasian Sparrowhawks (hereafter, sparrowhawks) were observed in 60‐ to 110‐year‐old coniferous forests dominated by Scots pine ( Pinus sylvestris ), with admixture of Norway spruce ( Picea abies ) and silver birch ( Betula pendula ). Observations were made primarily during field studies of wintering parids (Krams 1996, 1998a,b, 2000a,b, Krams et al 2001, 2013c, Krama et al 2008, 2015, Cīrule et al 2017).…”

“…For each attack by a sparrowhawk, we estimated the foraging height of the bird being attacked, tree height, and canopy height where the attacked bird was either captured or escaped. Foraging heights are normally expressed as proportions of canopy height and divided into four categories (Ekman 1986, Krams 1996, Cīrule et al 2017). In many cases, however, we were unable to determine the location in the canopy where predators killed their prey or where prey escaped.…”

How generalist are these forest specialists? What Sweden’s avian indicators indicate

“…Territory size varies according to habitat, but generally ranges from 5 to 15 ha (Gosler et al ., 2019). Some studies have concluded that this species prefers old forests (Solonen & Jokimaki, 2011; Cirule et al ., 2017; Gosler et al ., 2019), whereas other studies have failed to find such a preference (Virkkala et al ., 1994). Additional studies have found that willow tit prefer structurally complex forests (Eggers & Low, 2014) with standing decaying deciduous trees (Vatka et al ., 2014), especially in damp habitats (Lewis et al ., 2007).…”

Forest Resources Management and Sustainability: The Specific Case of European Union Countries

“…This is observed when managed forests are compared with unmanaged areas [49]. This is true for flora and fauna, where human interventions impact biodiversity resilience [50].…”