DOI: 10.5061/dryad.jsxksn05x
title: Evidence that stress-induced changes in surface temperature serve a thermoregulatory function

description: Changes in body temperature following exposure to stressors have been
 documented for nearly two millennia, however, the functional value of this
 phenomenon is poorly understood. We tested two competing hypotheses to
 explain stress-induced changes in temperature, with respect to surface
 tissues. Under the first hypothesis, changes in surface temperature are a
 consequence of vasoconstriction that occurs to attenuate blood-loss in the
 event of injury and serves no functional purpose per se; defined as the
 Haemoprotective Hypothesis. Under the second hypothesis, changes in
 surface temperature reduce thermoregulatory burdens experienced during
 activation of a stress response, and thus hold a direct functional value;
 here, the Thermoprotective Hypothesis. To understand whether
 stress-induced changes in surface temperature have functional
 consequences, we tested predictions of the Haemoprotective and
 Thermoprotective hypotheses by exposing Black-capped Chickadees (n=20) to
 rotating stressors across an ecologically relevant ambient temperature
 gradient, while non-invasively monitoring surface temperature (eye region
 temperature) using infrared thermography. Our results show that
 individuals exposed to rotating stressors reduce surface temperature and
 dry heat loss at low ambient temperature and increase surface temperature
 and dry heat loss at high ambient temperature, when compared to controls.
 These results support the Thermoprotective Hypothesis and suggest that
 changes in surface temperature following stress exposure have functional
 consequences and are consistent with an adaptation. Such findings
 emphasize the importance of the thermal environment in shaping
 physiological responses to stressors in vertebrates, and in doing so,
 raise questions about their suitability within the context of a changing
 climate.
description: <strong>## Readme</strong> This
 note contains necessary descriptions for understanding and working with
 data used in the construction of Robertson et al, 2020 (Journal of
 Experimental Biology). Below,<br> we list each file name attached to
 this data repository, and descriptions of the data contained within each
 column of a data file if it is a .CSV. Information pertaining to our R
 code (which has been provided in this data repository) has not been
 provided within this readme note, because necessary descriptions for
 understanding our code are provided within the R code file
 itself. <strong>Data
 files:</strong> <strong>1) "All
 Combined Thermal Data.csv".</strong> This
 CSV contains all ambient temperature and surface temperature measurements
 drawn from flight enclosures and individual Black-capped Chickadees
 (respectively) across each day of experimentation. Columns found within
 this data file are as follows: Column 1: Row numbers
 (not used in our analyses, but are residual from previous raw data frames
 that were bound in the construction of this final, master data
 sheet). Column 2: Dates from which ambient temperature
 and surface temperatures found in a row were drawn. Dates are in YYYYMMDD
 format and are treated as factors in our analyses.<br> <br>
 Column 3: The time at which an ambient temperature and surface temperature
 measurement found in a row were drawn, as measured in seconds (integer),
 with second 0 equaling 12:00 AM of a given day. Time was measured in
 seconds as surface temperature measurements were captured at a frequency
 of one frame per second. Column 4: Flight enclosure ID
 (a factor). This column contains the identity of a flight enclosure that
 the individual from which a surface temperature measurements was captured,
 was maintained. This experiment used 20 Black-capped Chickadees that were
 maintained across 4 flight enclosures (labelled by their cardinal
 position, with respect to other flight enclosures). Note that some
 enclosure IDs as labelled with their ID name, followed by "_2";
 such IDs are found on rows that contain surface temperature measurements
 that were captured during a second filming session of that
 individual's enclosure in a given day. Specifically, we rotated our
 thermal imaging camera among flight enclosures each day. If an
 individual's surface temperature was captured during the second
 session of filming, it's respective flight enclosure was labelled,
 "FLIGHTID_2", where "FLIGHTID" is replaced with the
 true identity of the flight enclosure.       <br> <br> Column
 5: Flight enclosure ID abbreviated (a factor). This column contains the
 equivalent data to that described in column 4, however, second filming
 sessions are not labelled as distinct from first filming sessions. The
 enclosure identity column was used for all analyses described in our
 study.<br> <br> Column 6: Maximum surface temperature of the
 eye region of a thermally imaged Black-capped Chickadee, in degrees
 Celsius (a continuous, numeric variable).<br> <br> Column 7:
 Quality of the thermal image from which surface temperature measurements
 contained in column 6 were drawn. Thermal images of individual that were
 captured during movement, and were thus blurry, were labelled "Poor
 Eye", whereas those captured during moments with no movement, and
 were thus in focus, were labelled "Good". Rows containing
 surface temperature measurements that had quality values of "Poor
 Eye" were excluded from our analyses.<br> <br> Column 8:
 Ambient temperature (a continuous, numeric variable) experienced during
 the time at which a surface temperature measurement contained in a given
 row was measured. Ambient temperature values were collected every 5
 minutes, and were assumed to remain constant from the time of collection
 to the second before the next temperature measurement was drawn.<br>
 <br> Column 9: Experimental treatment (a factor). Rows containing
 surface temperature measurements that were captured from individuals
 experiencing control treatments are labelled "Rest", while those
 captured from individuals experiencing stress exposed treatments are
 labelled "Stress".<br> <br> Column 10: Bird identity
 (a factor). The individual from which a surface temperature measurement in
 a given row was collected is identified by it's unique coloured
 leg-band combination here. <strong>2)
 "Full_Thermal_Data_With_Sexes.csv".</strong>
 This CSV contains identical data to that found within "All
 Combined Thermal Data.csv", however, additional factorial data
 pertaining to individuals from which surface temperature measurements were
 bound is also found within. Columns found within this data file are as
 follows: Columns 1 through 10: All data is as described
 for "All Combined Thermal Data.csv". Column
 11: Location of capture (a factor). The region that a given individual,
 from which a surface temperature measurement contained in a given row was
 captured, was collected from. All Black-capped Chickadees were captured
 across 6 different regions, and the regional name of each location of
 capture are found within this column. Column 12:
 Category of an individual's capture location (a factor). This column
 was not used in our analysis, but categorizes that capture locations found
 in column 11 as either "Urban" or "Rural".<br>
 <br> Column 13: Sex of an individual from which a surface
 temperature measurement in a given row was drawn (a factor); either
 "Male" or "Female".
 <strong>3)
 "Condition_Data.csv".</strong> This CSV
 contains relevant measurements of individuals used for analysing change in
 condition experienced by a Black-capped Chickadee across control and
 stress exposure treatments. Columns found within this data file are as
 follows:<br>         <br> Column 1: Row number (unused in our
 analysis, and residual from master data frame construction).
 Column 2: Individual identity of a given bird (factor), as
 defined by a unique coloured leg-band combination. Note that Chickadees
 were measured before and after each experimental treatment (stress
 exposure and control), and as such, four rows should be found for each
 individual.<br> <br> Column 3: Flight enclosure identity
 (factor). The flight enclosure from which an individual (whose data is
 represented in a given row) was maintained during experimentation.  
  <br> <br> Columns 4-6: Equivalent to columns 11-13 in
 "Full_Thermal_Data_With_Sexes.csv".<br> <br> Column
 7: Right wing chord measurement of a given individual defined within
 column 2 of the data row. Measured in mm.<br> <br> Column 8:
 Back of head to tip of bill measurement of a given individual defined
 within column 2 of the data row. Measured in mm.<br> <br>
 Column 9: Right tarsus measurement of a given individual defined within
 column 2 of the data row. Measured in mm.<br> <br> Column 10:
 Mass measurement of a given individual defined within column 2 of the data
 row. Measured in g.<br> <br> Column 11: Time-point at which
 measurements within a given row were collected (a factor), with respect to
 the beginning or end of a treatment (e.g. "Start" or
 "End"), and with respect to the treatment type (whereby control
 treatments are labelled as "Rest", and stress exposure
 treatments as labelled as "Stress").
 <strong>4) "Digital Bird with
 RT.csv".</strong> Lastly, this CSV contains
 data used for analyses of feeding rate according to experimental treatment
 among our Black-capped Chickadees, and for analyses of whether feeding
 rate correlates with surface temperature in our Black-capped Chickadees.
 It contains surface temperature measurements of Chickadees across dates,
 times, and experimental treatments, and contains an enumerated presence
 and absence column for use in feeding rate analyses. Columns within this
 data file are as follows: Columns 1-2: Equivalent to
 columns 2-3 in "All Combined Thermal Data.csv".<br>
 <br> Column 3: Equivalent to column 4 in "All Combined Thermal
 Data.csv".    <br> <br> Column 4: Time at which a surface
 temperature measurement contained within a given row was collected, as
 written in HHMMSS format, rather than absolute seconds format. This column
 is not used in our analyses, and is contained for simple visualization
 purposes.<br> <br> Columns 5-7: Equivalent to columns 6-8 in
 "All Combined Thermal Data.csv".<br> <br> Column 8:
 Equivalent to column 5 in "All Combined Thermal Data.csv".  
  <br> <br> Column 9: Equivalent to column 9 in "All
 Combined Thermal Data.csv".    <br> <br> Column 10: A
 duplication of column 1, but with a truncated column name for simplicity.
 Date from which a surface temperature measurement in a given row was
 captured.<br> <br> Column 11: Equivalent to column 5 in
 "All Combined Thermal Data.csv".<br> <br> Column
 12-16: Columns describing the presence (1) or absence (0) of a given
 individual (defined by the column name), at a given second of an
 experimental day, as defined by columns 1 and 2 of a given row. This
 experiment was conducted across 4 flight enclosures, with 5 individuals
 held within each flight enclosure; each column therefore pertains to the
 presence of absence of one specific individual in the flight enclosure
 identified in columns 3 and 11 for a given row. Note that the identities
 of individuals defined in each column, with respect to their unique
 coloured-leg band combinations, are identified within the attached r code.
 Importantly, not all rows containing a presence value (1) also have a
 corresponding surface temperature value, because the eye region of birds
 that were feeding could not always be viewed.<br> <br> Column
 17: A column defining the global presence (1) or absence (0) of any
 feeding birds (as identified in digital video), at any given time.