Artificial devices are increasingly used in conservation measures to mitigate the disappearance of natural habitats. However, few studies have demonstrated their benefits for the target species, and they may pose a risk of creating ecological traps. This occurs when lower individual fitness is found in artificial habitats that are more attractive than their natural equivalents. In this study, we tested the ecological trap hypothesis on a dense population of European rollers Coracias garrulus breeding in both natural cavities and nest-boxes. Our initial prediction was that the more stressful microclimatic conditions of nest-boxes would lead to reduced fitness of European rollers, thus creating an ecological trap. The results showed that nest-boxes were preferred over natural cavities. Despite significantly more extreme microclimatic conditions in nest-boxes, we found similar breeding parameters between artificial and natural nest types. Our results also suggest that European rollers selected the nest-boxes which best buffered the temperature, thus avoiding potential ecological traps. Overall our results led to the conclusion that nest-boxes do not create ecological traps for European rollers in this study area. However, other species may be more sensitive to microclimatic variations or less able to avoid the least favourable nest-boxes. These findings could help to inform the placement of nest-boxes in order to reduce extreme temperatures and variation in humidity rates. Future studies could compare nest types for other fitness parameters, such as juvenile body condition or survival. We also recommend the ecological trap hypothesis as a useful framework to evaluate the outcomes of artificial devices used for conservation.

See paper (open access)

Meaning of each column:

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alldata_microclimate_15days.csv

Name of the column	Description
Daily microclimate variables
MaxTint	Maximal temperature in the nest (°C)
MinTint	Minimal temperature in the nest (°C)
MoyTint	Mean temperature in the nest (°C)
DiffTint	Difference between maximal and minimal temperature in the nest (°C)
Dtmoyabs	Mean over a day of the absolute delta between interior and exterior temperature (°C)
Dtmaxabs	Absolute value of the daily maximum delta between interior and exterior temperature (°C)
Maxhum	Maximum humidity level in the nest (%RH)
Minhum	Minimum humidity level in the nest (%RH)
Moyhum	Mean humidity level in the nest (%RH)
DiffHum	Difference between maximal and minimal humidity level in the nest (%RH)
Name	Name of the nest-box or cavity
Type	Nest type : either nest-box or cavity
occupation	Occupation of the nest by rollers during the breeding season : 1 for roller nests, 0 otherwise
OccR	Real occupation of the nest during monitoring (roller or starling) : 1 for occupied nests sensor measurements, 0 for empty nests during sensor measurements
Developmental stage	Number of days between the day of measurement and the first egg-laying date (0 for nests not occupied by rollers)
First egg-laying date	Day of the laying of the first egg (for roller nests only) (Julian calendar date)
CH	Cavity height (m)
CBH	Circumference of the tree at breast height (1.30m) (cm) (natural cavities only)
CCH	Circumference of the tree at cavity height (cm) (natural cavities only)
Orientation	Entrance orientation of the nest (degrees)
Ori	Simplified orientation of the nest (either N, E, S or W with N: 316°-45°; E: 46°-135°; S: 136°-225°; W: 226°-315°)
EH	Entrance height (cavity) (mm) (natural cavities only)
EW	Entrance width (cavity) (mm) (natural cavities only)
CL	Cavity length (cm) (vertical) : minimum distance from the bottom of entrance hole to the bottom of the chamber (natural cavities only)
CD	Cavity depth (cm) (horizontal) : minimum distance from the entrance hole to the back wall of the cavity (natural cavities only)
Date	Day of the measurement (Julian calendar date)

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reproduction_data_2016-2019.csv

Name of the column	Description
Name	Name of the nest-box or cavity
Type	Nest type : either nest-box or cavity
year	Year of monitoring of the nest
eggs	Size of the clutch (complete clutches only)
chicks	Number of hatched eggs in complete clutches
fledglings	Number of fledglings
success	1 if at least 1 fledgling, 0 otherwise
n_failed_eggs	Number of eggs that did not produce a fledgling

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average_microclimate_&_characteristics_NB_CAV.csv

Name of the column	Description
Mean microclimate variables over 15 consecutive days
MAXTint	Maximal temperature in the nest (°C)
MINTint	Minimal temperature in the nest (°C)
MOYTint	Mean temperature in the nest (°C)
DIFFTint	Difference between maximal and minimal temperature in the nest (°C)
DTMOYabs	Mean over a day of the absolute delta between interior and exterior temperature (°C)
DTMAXabs	Absolute value of the daily maximum delta between interior and exterior temperature (°C)
MAXHum	Maximum humidity level in the nest (%RH)
MINHum	Minimum humidity level in the nest (%RH)
MOYHum	Mean humidity level in the nest (%RH)
DIFFHum	Difference between maximal and minimal humidity level in the nest (%RH)
Name	Name of the nest-box or cavity
Type	Nest type : either nest-box or cavity
occupation	Occupation of the nest by rollers during the breeding season : 1 for roller nests, 0 otherwise
OccR	Real occupation of the nest during monitoring (roller or starling) : 1 for occupied nests sensor measurements, 0 for empty nests during sensor measurements
CH	Cavity height (m)
CBH	Circumference of the tree at breast height (1.30m) (cm) (natural cavities only)
CCH	Circumference of the tree at cavity height (cm) (natural cavities only)
Orientation	Entrance orientation of the nest (degrees)
Ori	Simplified orientation of the nest (either N, E, S or W with N: 316°-45°; E: 46°-135°; S: 136°-225°; W: 226°-315°)
EH	Entrance height (cavity) (mm) (natural cavities only)
EW	Entrance width (cavity) (mm) (natural cavities only)
CL	Cavity length (cm) (vertical) : minimum distance from the bottom of entrance hole to the bottom of the chamber (natural cavities only)
CD	Cavity depth (cm) (horizontal) : minimum distance from the entrance hole to the back wall of the cavity (natural cavities only)