Territory-level temperature influences breeding phenology and reproductive output in three forest passerine birds

Temperature plays an important role in determining the breeding phenology
of birds in temperate climates, with higher spring temperatures associated
with earlier breeding. However, the effect of localised territory-scale
temperature variations is poorly understood, with relationships between
temperature and breeding phenology mostly studied using coarse-grained
climatic indices. Here, we interpolate spring temperatures recorded at 150
m2 grid intersections encompassing 417 ha of forest to examine the
influence of territory-scale temperature, and its interaction with mean
annual temperature, on territory selection, breeding phenology, clutch
size and fledging success for three co-occurring single-brooded passerine
birds using data from 672 nests over four years. All species exhibited
significant trends in reproductive traits associated with territory-scale
temperature. Pied flycatchers Ficedula hypoleuca settled in cooler
territories first, where they raised more fledglings. Blue tits Cyanistes
caeruleus laid larger clutches in warmer territories in warm years and
always laid earlier at warmer territories irrespective of annual
temperature variation. Contrastingly, pied flycatcher and wood warbler
Phylloscopus sibilatrix breeding phenology was earlier at warmer
territories in cool years and cooler territories in warm years, with wood
warbler clutch size responding similarly to this interaction. Greater
previous breeding experience and increased higher rates of historical
territory occupancy (territory quality) also predicted earlier breeding
phenology and higher fledging success for pied flycatchers. We suggest
that the migratory pied flycatcher and wood warbler are best synchronised
with their prey availability in cooler years at a local population level.
However resident blue tits match local phenology across all years, which
is potentially advantageous under warmer predicted climate change
scenarios. We conclude that temperature at the territory scale can be an
important driver of settlement and breeding phenology and influence
reproductive traits.