Effects of forest edge on nestling provisioning and nest vigilance of the globally endangered Giant Nuthatch (Sitta magna)

Forest fragmentation can have multiple effects on forest birds including nestling provisioning and parental behavior. Giant Nuthatch (Sitta magna) is globally endangered and inhabits border forests of Myanmar, China and Thailand that are highly threatened by habitat fragmentation. We conducted a comparison of nest provisioning and nest behavior of Giant Nuthatch in terms of provisioning rates, amount of prey delivered, and nest vigilance between forest interior and forest edge nests in northern Thailand. We collected data on (a) nest provisioning rates, (b) amount of prey delivered, and (c) adult nest vigilance at 10 nests during the 2023 breeding season. Generalized linear mixed models were used to examine variables influencing provisioning and parental behavior. Provisioning rates were ~42% higher at interior vs edge nests and the relative amount of prey delivered was ~61% higher at interior nests. There was no clear trend for vigilance between edge and interior nests. Although we consider the observed patterns to be preliminary due to our small sample size, we observed edge effects that may negatively impact parental foraging effort and provisioning of the Giant Nuthatch. While vigilance patterns were not clear, we hypothesize that vigilance rates are correlated with nest predation rates. Edge effects may negatively affect food delivery to Giant Nuthatch nestlings. Similar effects may occur in other forest-dependent insectivorous birds. Larger studies with direct measures of prey availability and predator abundances are needed to clarify mechanisms and inform conservation strategies.