10.5061/DRYAD.2BVQ83BRD
Courtois, Ève
0000-0003-4597-5605
Université de Sherbrooke
Bélisle, Marc
Université de Sherbrooke
Garant, Dany
Université de Sherbrooke
Pelletier, Fanie
Université de Sherbrooke
Nonideal nest box selection by tree swallows breeding in farmlands:
evidence for an ecological trap?
Dryad
dataset
2021
FOS: Biological sciences
Natural Sciences and Engineering Research Council
https://ror.org/01h531d29
Fonds de Recherche du Québec—Nature et technologies*
2022-11-04T00:00:00Z
2022-11-04T00:00:00Z
en
https://doi.org/10.22541/au.161832268.87346989/v1
609273 bytes
1
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Animals are expected to select a breeding habitat using cues that should
reflect, directly or not, the fitness outcome of the different habitat
options. However, human-induced environmental changes can alter the
relationships between habitat characteristics and their fitness
consequences, leading to maladaptive habitat choices. The most severe case
of such nonideal habitat selection is the ecological trap, which occurs
when individuals prefer to settle in poor-quality habitats while better
ones are available. Here we studied the adaptiveness of nest box selection
in a tree swallow (Tachycineta bicolor) population breeding over a 10-year
period in a network of 400 nest boxes distributed along a gradient of
agricultural intensification in southern Québec, Canada. We first
examined the effects of multiple environmental and social habitat
characteristics on nest box preference to identify potential settlement
cues. We then assessed the links between those cues and habitat quality as
defined by the reproductive performance of individuals that settled early
or late in nest boxes. We found that tree swallows preferred nesting in
open habitats with high cover of perennial forage crops, high spring
insect biomass, and high density of house sparrows (Passer domesticus),
their main competitors for nest sites. They also preferred nesting where
the density of breeders and their mean number of fledglings during the
previous year were high. However, we detected mismatches between
preference and habitat quality for several environmental variables. The
density of competitors and conspecific social information showed severe
mismatches, as their relationships to preference and breeding success went
in opposite direction under certain circumstances. Spring food
availability and agricultural landscape context, while related to
preferences, were not related to breeding success. Overall, our study
emphasizes the complexity of habitat selection behavior and provides
evidence that multiple mechanisms may potentially lead to an ecological
trap in farmlands.
Study area The study area included 40 farms distributed along a gradient
of agricultural intensification covering approximately 10,200 km2 in
southern Québec, Canada. Three land cover types dominated the study
system: low-intensity agricultural fields (i.e. hay, alfalfa (Medicago
sativa), clover (Trifolium spp.), and pastures, henceforth referred to as
“forage crops”), intensive agricultural fields (i.e., annual row crops
mainly composed of corn (Zea mays), soybean (Glycine max), and wheat
(Triticum spp.)) and forest. Each farm included 10 identical nest boxes
mostly arranged in a row along field margins and separated by at least 50
meters to limit intra and interspecific competition (see Ghilain and
Bélisle 2008 for further details on the study system). A Thermochron
iButton device was fixed on the outside of one nest box on each farm to
record hourly ambient temperature (model DS1922L; Embedded Data Systems,
Lawrenceburg, Kentucky, USA). A pluviometer collected precipitation data
(millimeters of rainfall) on each farm. We used the mean daily temperature
and mean daily rainfall between May 1 and May 15 to characterize spring
climate. Nest monitoring We monitored nest boxes every other day from
2009 to 2018 starting in the first week of May. We recorded the occurrence
of nest materials, the laying date (first egg), and the number of eggs,
hatchlings and fledglings. Monitoring ended when all nestlings had fledged
on a given farm, which occurred between June 15 and August 5 during the
study. Nest boxes were cleared of any nest material and/or dead nestlings
every year in October. Preference Preference for each nest box was
estimated for each year according to the occurrence of a laying event (at
least one egg laid) and settlement date (Julian date at which nesting
material was first observed). Because some early settlement dates were
left-censored given that some boxes already contained nest material at the
first visit (45% of all boxes), settlement dates were classified as either
“early” or “late” with respect to the annual median settlement date. The
category “early” included boxes with settlement dates preceding or equal
to the annual median, which comprised nearly all (91.3%) left-censored
dates. Overall, the average difference between the annual mean settlement
dates categorized as “early” and “late” was 10.4 ± 2.9 days (mean ± SD).
Nest boxes occupied by other species were excluded from analyses (N = 964
boxes between 2009 and 2018). Such exclusions were made possible, even in
the absence of a laying event, because the material and shape of nests are
very species specific. We are thus confident that the vast majority of
nests included in the study were initiated by tree swallows. The ordinal
preference variable featured three categories: 1: No laying event 2:
Laying event and late settlement 3: Laying event and early settlement
Habitat quality We used two proxies of reproductive success: (1) the
number of hatchlings produced in a nest box and (2) the proportion of
hatchlings that successfully fledged in a nestbox (i.e., fledging
success). Landscape context We characterized landscape habitat
composition by measuring the relative cover of forest, perennial forage
crops, as well as of water bodies and wetlands, within radii of
respectively 100 m, 5 km and 10 km. We assessed landscape habitat
composition up to the 500-m scale on a yearly basis in the field by
visually identifying cultures and marginal habitats and delineating them
using orthophotos (1:40,000). Characterization beyond the 500-m scale was
based on a mosaic of yearly georeferenced classified optical and radar
satellite images taken between 2011 and 2018 (pixel resolution 30 m ×
30 m; Agriculture and Agri-Food Canada (AAFC) 2018). Only the year 2018
was used to assess water cover at the above range of scales because it
showed better accuracy than the data of previous years (AAFC, 2020), and
because the cover of large water bodies, as those covered by the data we
used, did not vary significantly across years (e.g., median between-year
correlation of yearly water cover between 2011 and 2018 was 0.90 at the
10-km scale). Food availability Two passive insect traps were installed
on each farm around the first and second third of the nest box transect.
Traps consisted of ~4-L yellow buckets placed 1.5 m above ground. They
were filled with ~2 L of salty detergent solution to reduce surface
tension and slow the growth of bacteria and fungi. Two transparent
plexiglass screens were mounted perpendicularly to one another above each
bucket to intercept flying insects (see Bellavance et al. 2018 and Garrett
et al. 2021a for details). We collected the content of each trap on every
visit to a farm (i.e., every other day) and conserved arthropods in 70%
ethanol until processing. We sorted samples by removing arthropods
unlikely to be preyed upon by tree swallows (i.e., bumble bees (Bombus
spp.: Hymenoptera), June bugs (Phyllophaga spp.: Coleoptera), large
spiders (Araneae, > 0.5 cm body width), and caterpillars
(Lepidoptera); Bellavance et al. 2018). The rest of the sample was dried
at 50ºC for at least 48 hours before being weighed (Adam Equipment, model
AAA250L, ± 0.0001 g). The mean daily dry biomass of arthropods collected
between May 1 and May 15 was used as a proxy of yearly food availability
on a given farm at the time of nest site selection. Heterospecific
social information House sparrows (Passer domesticus) are tree swallow’s
main nest-site competitors in our system and they initiate breeding before
swallows return from their wintering grounds (Robillard, Garant and
Bélisle, 2013). We evaluated the use of heterospecific social information
through the number of nest boxes occupied by house sparrows on each farm
in the current year. Nest boxes and house sparrow nests were visited every
other day concurrently to tree swallow monitoring. Occupancy was
determined by the presence of at least one egg, and only first clutches
observed in each box were included since a nest box is rarely used by
another species once house sparrows have built a nest therein. Conspecific
social information We defined two sources of social information regarding
the future breeding success that an individual could expect to experience
on a given farm: the density of tree swallows that bred on a farm during
the previous year and the mean number of fledglings obtained by those
breeders.