Stable isotope composition of feathers and foraging behavior parallel bill shape divergence of Island Scrub-Jays (Aphelocoma insularis) in pine and oak habitats
Data files
Aug 29, 2025 version files 381.73 KB
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foraging_data_all_clean.csv
325.06 KB
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ISSJ_Foraging.Rmd
36.26 KB
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ISSJ_IsotopeData_all.csv
8.14 KB
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README.md
12.28 KB
Abstract
Individual differences within populations have important ecological and evolutionary implications for understanding population-level responses to environmental variation. We found evidence of habitat-linked differences in stable isotopic composition of feathers and foraging behavior of Island Scrub-Jays (Aphelocoma insularis), endemic to Santa Cruz Island, California, USA, which parallel phenotypic divergence in jay bill shape between pine and oak habitats. We used stable isotopes of hydrogen (δD), carbon (δ13C), and nitrogen (δ15N) from feathers and direct observations of foraging behavior to infer habitat-specific diet variation among Island Scrub-Jays. Although hydrogen isotope composition of feathers did not differ between habitats as we expected, jays sampled in pine habitat were more enriched in 13C, whereas jays sampled in oak habitat were more enriched in 15N. Foraging observations indicated that diets largely overlapped in the 2 habitats, but jays in pine were more likely to consume arthropods. Jays in pine habitat also used relatively more probing, sallying, and pecking foraging maneuvers to capture prey. These findings suggest new avenues of research for understanding how habitat-linked, phenotypic divergence shapes behavior and diet of the omnivorous Island Scrub-Jay.
Dataset DOI: 10.5061/dryad.q83bk3jpb
Description of the data and file structure
Foraging data: Opportunistically collected foraging data between September to November 2009-2012 from Island Scrub-Jays on Santa Cruz Island. For focal observations, observers waited for 5 min for an individual to acclimate to their presence before observing foraging through binoculars and recording details into digital voice recorders. We recorded the following details: food item taken (insect, acorn, fruit, seed), whether the individual was successful at taking the food item (consuming, carrying away), and foraging maneuver.
Stable isotope data: Measured δD, δ15N, and δ13C in breast feathers collected from 50 adult (>1-year-old) Island Scrub-Jays between 2009 and 2011. Analyses were conducted at the Smithsonian Stable Isotope Mass Spectrometry Laboratory in Suitland, Maryland, in September 2011–April 2012.
Files and variables
File: ISSJ_Foraging.Rmd
Description: R code to run all analyses
File: foraging_data_all_clean.csv
Description: Opportunistically collected foraging data between September to November 2009-2012 from Island Scrub-Jays on Santa Cruz Island. For focal observations, observers waited for 5 min for an individual to acclimate to their presence before observing foraging through binoculars and recording details into digital voice recorders. We recorded the following details: food item taken (insect, acorn, fruit, seed), whether the individual was successful at taking the food item (consuming, carrying away), and foraging maneuver.
Variables
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color_ban_lr: The banding scheme is such that birds are banded with an aluminum band on their right leg with two color bands beneath the aluminum, one denoting the location on the island in which it was banded and the other denoting its cohort.
The left leg of each bird has been banded with a unique combination of three color bands. The only exception to this rule is at the Field Station, where the older birds were banded by Charlie Collins and have two bands on each leg.
In contrast to the adults, birds banded as nestlings prior to 2013 have an aluminum band on their left leg (or legs get mixed up during banding), with a color band on the same leg corresponding to the plot where they hatched. If the birds were recaptured then three color bands were added to their right leg. This banding scheme was designed to facilitate the identification of birds banded as nestlings and, in particular, to make every effort to pay special attention to and track down birds that have a color band indicating that they were banded on a different part of the island.
The band abbreviations are as follows:
A = aluminum P = purple
R = red K = pink
G = green B = black
O = orange U = blue
W = white
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sex: male = M, female= F, U= unknown
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plot: refers to the study plot the birds was sampled from.
o PZ- Portezuela
o FS- Field Station
o CPC- Coches Prietos
o CEN- Centinela (same as Buena Vista, “BV”, in Figure 1)
o Christy- pines west of Centinela
o SZ Off-Plot – anywhere not on one of the listed plots
o SZ IS - Isthmus (Navy site in Figure 1)
o Pelican- pines North of Field Station
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habitat: Plots (see above) are classified as “pine” or “oak”, based on prior studies (Langin et al. 2015; Cladwell et al. 2013). Pine = Christy, CEN, Pelican; Oak= CPC, FS, PZ, IS
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date: date the observation was made (month/day/year)
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year: year observation was made
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focal_observation: (yes, no) observation was collected for 30 minute focal.
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substraight: Substrate (ground, air [AERO], plant species or type)
Veg Codes Common name Latin name ADFA Chamise Adenostoma Fasciculatum ARCA Sagebrish Artemesia californica ARDO Mugwort Artemesia douglasiana ARSP Manzanita Arctostaphylos spp. BAPL Plummers Baccharis Baccharis plummerae BAPI Coyote brush Baccharis pilularis BASA Mulefat Baccharis salicifolia CEAR California lilac Ceanothus arboreus CEME Bigpod ceanothus Ceanothus megacarpus CETR Mountain mahogany Cercocarpus... CODI Summer holly Comarostaphylis diversifolia DEAD Dead veg DEHA Island bush poppy Dendromecon harfordii DEPI Dead Pine DEPID Dead Pine Down DEPIU Dead Pine Upright ERFA Buckwheat Eriogonum spp. FORB Forbes of grass Family Poaceae FOVU Fennel Foeniculum vulgare HADE Island Bristleweed Hazardia detonsa HEAR Toyon Heteromeles arbutifolia KECO Climbing penstemmon Keckiella cordifolia LAVE Wild pea Lathyrus vestitus LODE Island deerweed Lotus dendroideus LYFL Ironwood Lyonothamnus floribundus MALL Mallow spp. Family Malvaceae MARA Wild cucumber Marah spp. MIMU Monkeyflower Mimulus spp. NONE No species PIMU Bishop pine Pinus muricata POFR Cottonwood Populus freemontii PRIL Island Cherry Prunus ilicifolia QUAG Live oak Quercus agrifolia QULO Valley oak Quercus lobata QUMA MacDonald's oak Quercus macdonaldii QUPA Scrub oak Quercus pacifica RHCR Red berry Rhamnus crocea RHIN Lemonade berry Rhus integrifolia RHOV Sugar bush Rhus Ovata RITH SCI Gooseberry Ribes thacherianum SALA Arroyo willow Salix lasiolepis SAME Black sage Salvia mellifera SNAG Tree snag/ upright log TODI Poison oak Toxicodendron diversilobum UNKN Unknown plant VECA Canyon Sunflower Venegasia carpesioides COGI Giant coreopsois SOCL Island Nightshade Solanum clokeyi -
substraight_material: substrate material (for ground: soil, grass, moss, rock, leaf-litter, etc; for plants: leaves, flowers, bark, fruit; for air: not applicable)
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foraging_maneuver: Foraging maneuver (definitions from Remsen & Robinson 1990)
o Glean: to pick food items from a nearby substrate, including the ground, that can be reached without full extension of legs or neck; no acrobatic movements are involved.
o Reach: to extend completely the legs or neck upwards, outwards, or downwards to reach food.
o Hang: to use legs and toes to suspend the body below the feet to reach food that cannot be reached from any other perched position.
o Lunge: those maneuvers in which the food item is beyond the range of “reach,” but rapid leg movements rather than flight are used to approach and capture prey (e.g. on ground).
o Probe: to insert the bill into cracks or holes in firm substrate or directly into softer substrate such as moss or mud to capture hidden food.
o Peck: to drive the bill against the substrate to remove some of the exterior of the substrate.
o Flake: to brush aside loose substrate with sideways, sweeping motions of the bill.
o Pry: to insert the bill into a substrate and use it as a lever to lift up portions of substrate.
o Scratch: to dislodge section of substrate with foot movements.
o Sally: to fly from a perch to attack a food item (and then return to a perch)
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food: NA if no food was obtained, UNK if observer could not tell. Observers identified prey species through binoculars and only recorded prey items if they could actually see the prey item
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successful: (yes no) did the individual consume or carry away the food item
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comment_1: note of any observations on individuals thought to be floaters, observations made during unfavorable weather, and anything else that was thought to be noteworthy
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comment_2: note of any observations on individuals thought to be floaters, observations made during unfavorable weather, and anything else that was thought to be noteworthy
File: ISSJ_IsotopeData_all.csv
Description: Measured δD, δ15N, and δ13C in breast feathers collected from 50 adult (>1-year-old) Island Scrub-Jays between 2009 and 2011. Analyses were conducted at the Smithsonian Stable Isotope Mass Spectrometry Laboratory in Suitland, Maryland, in September 2011–April 2012.
Variables
- aluminum_band: Unique numerical code associated with the United States Geological Survey bird banding program.
- tissue_number: The acquisition number given to each unique tissue.
- date_banded: the data the individuals was banded and sampled
- Year: the year the individual was sampled
- age: Age at the banding record is denoted as : N (Nestling), HY (Hatch Year), SY (Second Year), or AHY/ASY (After Hatch Year/After Second Year).
- Sex: male = M, female= F, U= unknown
- Mates_band: The USGS aluminum band combination for the individua;s mate (if from a mated pair).
- dD: Relative abundance of deuterium (H2) in the sample
- d15N: Relative abundance of N15 in the sample
- d13C: Relative abundance of C13 in the sampl
- d34S: Relative abundance of S34 in the sample
- location: refers to the study plot the birds was sampled from.
- PZ- Portezuela
- FS- Field Station
- CPC- Coches Prietos
- CEN- Centinela (same as Buena Vista, “BV”, in Figure 1)
- Christy- pines west of Centinela
- SZ Off-Plot – anywhere not on one of the listed plots
- SZ IS - Isthmus (Navy site in Figure 1)
- Pelican- pines North of Field Station
- habitat: Plots (see above) are classified as “pine” or “oak”, based on prior studies (Langin et al. 2015; Cladwell et al. 2013). Pine = Christy, CEN, Pelican; Oak= CPC, FS, PZ, IS
- plot: (see location)
- longitude: the longitude where an individual was captured and sampled
- latitude: the latitude where an individual was captured and sampled
- percent_pine: The proportion of pine vegetation within 300-meters of an individual's sampling location.
- percent_oak: The proportion of oak vegetation within 300-meters of an individual's sampling location
- percent_other: The proportion of “other” (e.g. grasslands, bare ground, scrub) vegetation within 300-meters of an individual's sampling location
Code/software
R code to run all analyses included in the ISSJ_Foraging.Rmd
- Yeatts, Brooke; Cheek, Rebecca G.; Mouton, James C. et al. (2025). Stable Isotope Composition of Feathers and Foraging Behavior Parallel Bill Shape Divergence of Island Scrub-Jays (Aphelocoma insularis) in Pine and Oak Habitats. Western North American Naturalist. https://doi.org/10.3398/064.085.0214