Data and R-code from: Migration, habitat and hunting style do not affect the malar stripe of different falcon species

Published Mar 04, 2025 on Dryad. https://doi.org/10.5061/dryad.cc2fqz6gg

Data files

Mar 04, 2025 version files 2.56 MB

dat_total.csv

2.56 MB
README.md

5.64 KB

Abstract

The solar glare hypothesis suggests that malar stripe of a falcon decreases the sun’s glare in the eye, possibly increasing their hunting success. The amount of sunlight an individual experiences could be affected by its migratory strategy, hunting strategy, or main habitat. However, it is not known if these environmental variables impact the size and intensity of the malar stripe. Therefore, this study aimed to analyse differences in size and intensity of malar stripes between individuals of twelve falcon species with different migratory strategies, habitats, and hunting styles distributed worldwide. The malar stripes of twelve falcon species were measured and scored using more than 6000 photos from citizen science repositories. The measurements of the malar stripes were first reduced with a principal component analysis (PCA) and then analysed using a linear mixed model that included migratory strategy, habitat, and hunting style as fixed factors and several posture variables as random factors. The relationships between the measurements of the malar stripe and solar radiation of the individual’s location were also analysed using linear mixed models. Overall, we found no differences in malar stripe size and intensity between species with differing migratory strategies, habitat and hunting styles. The relationships between various characteristics of the malar stripe and solar radiation did depend on the species and the habitat the individual occupied. Therefore, migratory strategy, habitat, and hunting style do not markedly influence the size and intensity of malar stripes across falcon species, suggesting that other mechanisms, such as thermoregulation or camouflage, also play a role.

https://doi.org/10.5061/dryad.cc2fqz6gg

Description of the data and file structure

Files and variables

File: dat_total.csv

Description: Measurements and scores for different aspects of the malar stripe for 12 falcon species.

Variables

ID: unique identifier for each photo
Library: online citizen science repositories
Eye_width_1: First measurement of eye width on the picture (in centimeters, cm hereafter)
Eye_width_2: Second measurement of eye width on the picture (cm)
Eye_width_3: Third measurement of eye width on the picture (cm)
Eye_heigth_1: First measurement of eye height on the picture (cm)
Eye_heigth_2: Second measurement of eye height on the picture (cm)
Eye_heigth_3: Third measurement of eye height on the picture (cm)
Width_template: Score of malar stripe width based on the scoring template
Width_measure_1: First measurement of malar stripe width on the picture (cm)
Width_measure_2: Second measurement of malar stripe width on the picture (cm)
Width_measure_3: Third measurement of malar stripe width on the picture (cm)
Contiguity: Score of malar stripe contiguity based on the scoring template
Prominence: Score of malar stripe prominence based on the scoring template
Length_template: Score of malar stripe length based on the scoring template
Length_measure_1: First measurement of malar stripe length on the picture (cm)
Length_measure_2: Second measurement of malar stripe length on the picture (cm)
Length_measure_3: Third measurement of malar stripe length on the picture (cm)
Head_vertical: Vertical position of the head based on the scoring template
Head_horizontal: Horizontal position of the head based on the scoring template
Head_rotation: Rotation of the head based on the scoring template
Compression: Compression of the head based on the scoring template
nr_individuals_on_photo: Number of individuals on the picture
Data_analyse: Date and time when the picture was analyzed
Common_name: Common name of the falcon species
Scientific_name: Scientific name of the falcon species
Date: Date at which the picture was taken
Country: Country in which the picture was taken
Latitude: Coordinates at which the picture was taken
Longitude: Coordinates at which the picture was taken
State: State or region in which the picture was taken
Solar: Average direct normal irradiation (kWh/m2) based on the Global Solar Atlas
Eye_width_average: Average of eye width based on three measurements (cm)
Eye_heigth_average: Average of eye height based on three measurements (cm)
Width_average: Average of malar stripe width based on three measurements (cm)
Length_average: Average of malar stripe length based on three measurements (cm)
Width_Relative_to_eye: Width of malar stripe relative to the eye width
Length_Relative_to_eye: Length of malar stripe relative to the eye length
Elongation_template: Elongation of the malar stripe based on the scoring template
Elongation_Relative_to_eye: Elongation of the malar stripe relative to the eye length
Species: Common name of falcon species
Migratory_strategy: Categorical variable with levels migratory, partially migratory and sedentary
Habitat: Categorical variable with levels grassland, shrubland, woodland, and forest
Surface: Surface of the malar stripe based on the scoring template
Surface_Measured: Surface of the malar stripe based on measurements of width and length (cm²)
Hunting_style: Categorical variable with levels aerial, generalist and insessorial

Code/software

R-script to analyze the analyze the differences in size and intensity of malar stripes between individuals of twelve falcon species with different migratory strategies, habitats, and hunting styles distributed worldwide. We used the latest versions of package tidyverse, lme4, car and lsmeans.

Input = the csv-file that belongs to this Dryad-entry

Workflow

Create subsets of the data for each of the sedentary subspecies (will be analyzed later on)
Determine data distribution of each variable of the malar stripe
1. For all 12 species together
2. For the four sedentary species (bat falcon, brown falcon, New Zealand falcon, Red-necked falcon)
3. For each sedentary species separately
Run linear mixed models for each variable of the malar stripe with migratory strategy, habitat and hunting style as fixed factors
1. For all 12 species together
2. For the four sedentary species (bat falcon, brown falcon, New Zealand falcon, Red-necked falcon)
3. For each sedentary species separately
Run linear mixed models for each variable of the malar stripe with solar radiation as fixed factor (only for sedentary species)
1. For the four sedentary species (bat falcon, brown falcon, New Zealand falcon, Red-necked falcon)
2. For each sedentary species separately

Access information

Other publicly accessible locations of the data:

AVONET-database: https://onlinelibrary.wiley.com/doi/full/10.1111/ele.13898

Data was derived from the following sources:

iNaturalist (https://www.inaturalist.org/, open source data)
Macaulay Library (https://search.macaulaylibrary.org/, open source data)

For this study, we compared the malar stripes of 12 falcon species with differing migratory strategies (migratory, partially migratory, and sedentary), habitats (grassland, woodland, shrubland and forest), and hunting styles (aerial, insessorial and generalist). We used two online citizen science repositories, iNaturalist (iNaturalist, n.d.) and the Macaulay Library (Macaulay Library, n.d.), to get access to photos of the 12 different falcon species.

Table 1. The 12 falcon species included in this study with their migratory strategy, habitat, and hunting style.

Scientific name	English name	Migratory strategy	Habitat*	Hunting style
Falco amurensis	Amur Falcon	Migratory	Grassland	Insessorial
Falco columbarius	Merlin	Migratory	Woodland	Aerial
Falco naumanni	Lesser Kestrel	Migratory	Grassland	Generalist
Falco subbuteo	Eurasian Hobby	Migratory	Woodland	Aerial
Falco cenchroides	Australian Kestrel	Partially Migratory	Woodland	Generalist
Falco biarmicus	Lanner Falcon	Partially Migratory	Shrubland	Aerial
Falco sparverius	American Kestrel	Partially Migratory	Grassland	Insessorial
Falco tinnunculus	Eurasian Kestrel	Partially Migratory	Shrubland	Aerial
Falco berigora	Brown Falcon	Sedentary	Woodland	Aerial
Falco chicquera	Red-necked Falcon	Sedentary	Woodland	Aerial
Falco novaeseelandiae	New Zealand Falcon	Sedentary	Forest	Aerial
Falco rufigularis	Bat Falcon	Sedentary	Forest	Aerial

For each species, we analysed 500 photos that were equally distributed over its distribution range. Per individual, we measured and calculated six measurements of the malar stripe: the width of the malar stripe, which is the thickness of the stripe; the contiguity with the hood, which is the connection of the malar stripe to the dark plumage on the hood; the prominence, which is the intensity of the malar stripe; the length of the malar stripe which is the maximum distance from the dorsal to the ventral end of the stripe; the elongation, which is calculated by dividing the length by the width; and the surface, which is calculated by multiplying the width by the length.

The width and length were measured using an on-screen measuring tool (Aequo), and these two measures were used to calculate the elongation and surface of the malar stripe. The contiguity and prominence were scored using a scoring template. We also scored the width and length of the malar stripe and used these scores to calculate a scored elongation and surface. Because the position of the birds varied a lot throughout the photos, the measurements were done relative to the width and height of the bird’s eye. We performed each measurement three times and used the average of these measurements in the analysis. Also, the bird's posture was scored using a scoring template.

Finally, we obtained the average direct normal irradiation (kWh/m²) using a Global Solar Atlas for each region a photo was taken in. The Handbook of Energy, "Section 10 - Solar" (2013) stated that “Direct Normal Irradiation (DNI) is the amount of solar radiation received per unit area by a surface that is always held perpendicular (or normal) to the rays that come in a straight line from the direction of the sun at its current position in the sky.” Hence, we used direct normal irradiation as a proxy for the amount of sunlight an individual experiences throughout the year.