DOI: 10.5061/dryad.dv41ns1vs
title: Data from: Phenological delay despite warming in wood frog (Rana sylvatica) reproductive timing: a 20-year study

description: Across all taxa, amphibians exhibit some of the strongest phenological
 shifts in response to climate change. As climates warm, amphibians and
 other animals are expected to breed earlier in response to temperature
 cues. However, if species use fixed cues such as daylight, their breeding
 timing might remain fixed, potentially creating disconnects between their
 life history and environmental conditions. Wood frogs (Rana sylvatica) are
 a cold-adapted species that reproduce in early spring, immediately after
 breeding ponds are free of ice. We used long-term surveys of wood frog
 oviposition timing in 64 breeding ponds over 20 years to show that,
 despite experiencing a warming of 0.29 °C per decade in annual
 temperature, wood frog breeding phenology has shifted later by 2.8 days
 since 2000 (1.4 days per decade; 4.8 days per °C). This counterintuitive
 pattern is likely the result of changes in the timing of snowpack
 accumulation and melting. Finally, we used relationships between climate
 and oviposition between 2000 and 2018 to hindcast oviposition dates from
 climate records to model longer-term trends since 1980. Our study
 indicates that species can respond to fine-grained seasonal climate
 heterogeneity within years that is not apparent or counterintuitive when
 related to annual trends across years.
description: Climate data: We extracted daily meteorological data, including
 maximum and minimum temperature, precipitation, and snowpack (quantified
 as snow water equivalent) from the DayMet database (v.3 (Thornton et al.
 2016)). The Daymet algorithm uses daily meteorological observations from
 ground stations to interpolate estimates at 1km square cells across North
 America between 1980 and 2018. We extracted estimates for the cell
 centered nearest the geographical center of our site (tile: 11754, N
 41.9198 W -72.1604). Oviposition data: These data
 include records of annual egg-mass surveys collected between 2000 and 2019
 for 64 wood frog breeding ponds at Yale Myers Forest, a 3,213 ha research
 forest in northeastern Connecticut, USA. During surveys, the entire pond
 was closely searched by observers. If eggs were found, the observers
 independently counted and then averaged the estimates (or, in cases of
 surveys by a single observer, egg masses were counted twice and
 averaged). Microhabitat data: We include microhabitat
 data for wood frog breeding ponds at our site including: latitude,
 elevation, aspect, and a suite of canopy metrics estimated from repeated
 hemispherical photos. Briefly, five hemispherical photographs were take
 along the shore at each cardinal point and at the center of each pond
 during leaf-off and leaf-on seasons. We used Gap Light Analyzer (Frazer
 1999) to estimate average leaf-on and leaf-off global site factor (GSF;
 the ratio of above-canopy radiation to under-canopy radiation (Anderson
 1964)) and a weighted GSF value integrated over the duration of wood frog
 larval and embryonic life cycle (Halverson et al. 2003). Additionally, we
 included the within-pond variance in GSF values, which captures important
 components of the canopy shape and structure above and surrounding the
 ponds. Point values for aspect and elevation were estimated from the USGS
 National Elevation Dataset (U.S Geological Survey 2002). In addition, we
 included site-wide daily average temperature, precipitation, and SWE
 between day-of-year 0 and 120 (Jan 1 ~ April 29) from the DayMet dataset.
 This range spans the earliest and latest observed oviposition dates
 (day-of-year 74 and day-of-year 113) with a margin.
 Code: R code to replicate the analysis is included with further
 instructions inline in the scripts.