DOI: 10.5061/dryad.7m41jd8
title: Data from: Rainy springs linked to poor nestling growth in a declining avian aerial insectivore (Tachycineta bicolor)

description: As species shift their ranges and phenology to cope with climate change,
 many are left without a ready supply of their preferred food source during
 critical life stages. Food shortages are often assumed to be driven by
 reduced total food abundance, but here we propose that climate change may
 cause short-term food shortages for foraging specialists without affecting
 overall food availability. We frame this hypothesis around the special
 case of birds that forage on flying insects for whom effects mediated by
 their shared food resource have been proposed to cause avian aerial
 insectivores’ decline worldwide. Flying insects are inactive during cold,
 wet, or windy conditions, effectively reducing food availability to zero
 even if insect abundance remains otherwise unchanged. Using long-term
 monitoring data from a declining population of tree swallows (Tachycineta
 bicolor), we show that nestlings’ body mass declined substantially from
 1977 to 2017. In 2017, nestlings had lower body mass if it rained during
 the preceding three days, though females increased provisioning rates,
 potentially in an attempt to compensate. Adult body mass, particularly
 that of the males, has also declined over the long-term study. Mean
 rainfall during the nestling period has increased 9.3±0.3 mm/decade,
 potentially explaining declining nestling body mass and population
 declines. Therefore, we suggest that reduced food availability, distinct
 from food abundance, may be an important and previously overlooked
 consequence of climate change, which could be affecting populations of
 species that specialize on foraging on flying insects.
description: Long term nestling body
 size data10-16 day old tree
 swallow nestlings body size measurements from 1977-2017. Column names are
 as follows: nestlingID = Unique ring Canadian Wildlife Service number
 identifying individual nestlings, nestID=Unique code for each nest, year=
 year, age=number of days since hatching (e.g., on the hatch date, age=0)
 in days, hatchdate=date most of the nestlings hatched (tree swallows
 typically hatch synchronously) (Julian date), hatchsize=number of hatched
 nestlings, fledgedate=date most of the nestlings fledged or the nest
 failed (Julian date), fledgesize =number of nestlings that fledged,
 mass=nestling body mas (g), tarsus=nestling tarsus length (mm), ninprim=
 nestling wing chord (mm), year2= decades since 1977 (the first year
 nestlings were measured)Long term adult body
 size dataAdult body size records
 from 1983-2017. Column headings are as follows: band=unique ring Canadian
 Wildlife Service number identifying individual birds, year=year , sex=male
 (M) or female (F), age=males are listed as AHY (after hatch year) when
 caught as adults initially. Females may be aged by plumage as SY (second
 year, a one-year-old bird) or ASY (after second year, and 2+ years old).
 Birds caught subsequently are listed based on their age as first capture
 (e.g. A3Y (after third year), 4Y (four years old), mass=adult’s body mass
 (g), tarsus=adult’s tarsus length (mm), wingChord=adult’s wing chord (mm),
 nestID=nest box identifier, not unique, laydate=date the first egg was
 laid (Julian date), incdate=date the last egg was laid, when incubation
 begins (julian date), hatchdate=date most of the nestlings hatched (tree
 swallows typically hatch synchronously) (Julian date), fledgedate=date
 most of the nestlings fledged or the nest failed (Julian date),
 dateMeas2=date mass, tarsus, and wing chord measurements were taken
 (Julian date), year2=years since 1975, when adults were first captured,
 diff=days between when eggs were first laid and when the bird was measured
 (dateMeas2-laydate), Period=Was the nest in the incubation stage or the
 nestling stage?Nestling growth data
 2017Detailed nestling growth
 records with weather conditions in 2017. Nestlings were measured on day 2,
 4, 6, 8, 10 and 12. Column headings are as follows: NestlingID=unique ring
 Canadian Wildlife Service number identifying individual nestlings,
 NestID=unique code for each nest, HatchSize=number of hatched nestlings,
 HatchDate=date most of the nestlings hatched (tree swallows typically
 hatch synchronously) (Julian date), FledgeDate=date the nest fledged
 (Julian date), FledgeSuccess=0 if this nestling did not fledge, 1 if it
 did, whyFail=If the nest failed, lists the cause, either “NESTLINGS DIED”
 if nestlings were found dead in the nest, or “PREDATION” if no nestlings
 were found, Renest=lists whether nest was a renest or not. All nests used
 in this analysis were the first nest of the pair, Mass=nestling body mass
 (g), Tarsus=nestling tarsus length (mm), Wingchord=nestling wing chord
 (mm), Age=number of days since hatching (e.g., on the hatch date, age=0),
 MaxTemp3day=mean value of the maximum daily temperatures during the
 preceding three days (°C), MeanTemp3day=mean value of the mean daily
 temperatures during the preceding three days (°C), MeanWindspeed3day=Mean
 value of the mean windspeed (5:30am-8pm) during the preceding three days
 (m/s), TotalRainFall3day=total rainfall during the preceding three days
 (mm), ThermoReg=thermoregulatory strategy employed by nestlings of this
 age (poikilothermic (0-6 days old), intermediate (7-8 days old), or
 endothermic (9+ days old))Provisioning rate data
 20172017 provisioning rates
 for tree swallows with weather data. Column headings as follows:
 boxID=nest box ID (not unique), ffv=female provisioning rate (feeding
 visits/hr), mfv=male provisioning rate (feeding visits/hr),
 NestlingsAlive=The number of nestlings in the nest on the date
 provisioning rate was measured, Date=Date provisioning rate was measured
 (YYYY-mm-dd), meanwindspeed=mean windspeed from 5:30am-8pm on the day we
 measured provisioning rate (m/s), MaxTemp=maximum daily temperature on the
 day we measured provisioning rate (°C), TotalRain_3day=total rainfall in
 the three days preceding when we measured provisioning rate (mm),
 TotalRain_3day2= “Rain” if it had rained more than 3mm in the preceding
 days, otherwise “None”Long term nestling body
 size analysisR code for the long term
 nestling body size analysisLong term adult body
 size analysisR code for the long term
 adult body size analysisNestling growth analysis
 2017R
 code for the nestling growth analysis in 2017Provisioning rate
 analysis 2017R code for the
 provisioning rate analysis in 2017