Data from: Good guardian, bad parent: tradeoffs between territory defense and parental care in Darwin’s finches

Katsis, Andrew 1 ; Common, Lauren1 ; Akçay, Çağlar 2 ; Kleindorfer, Sonia 1

Research facility: Konrad Lorenz Research Center for Behavior and Cognition

Published Sep 15, 2025; Updated Sep 22, 2025 on Dryad. https://doi.org/10.5061/dryad.np5hqc072

Data files

Sep 15, 2025 version files 1.94 MB

Sep 22, 2025 version files 99.24 MB

Abstract

Although defending a territory may benefit individuals by allowing them to retain important resources, the time and energy costs associated with territory defense may lead territory owners to neglect other reproductively important behaviors. In this study, we assessed the potential trade-off between territory defense and parental care in four Darwin’s finch species on Floreana Island, Galápagos. First, using song playback, we simulated territory intrusions to measure male aggressiveness across multiple stages of the breeding cycle (unpaired, paired, incubating, and chick feeding). We conducted 168 playback trials at 98 nests (37 small ground finch, 28 medium tree finch, 27 small tree finch, 6 cactus finch). To quantify parental care at each nest, we conducted one-hour observations to record the frequency of male food deliveries and the duration of female incubation and brooding. We conducted 113 parental care observations at 59 nests (24 small ground finch, 18 small tree finch, 15 medium tree finch, 2 cactus finch). By breeding stage, we conducted 76 observations at 53 nests during the incubation period (mean ± SE observations per nest = 1.43 ± 0.07, range 1–3) and 37 observations at 28 nests during the chick feeding period (1.32 ± 0.12 observations per nest, range 1–3).

Andrew C. Katsis^1,2*, Lauren K. Common^1,2, Çağlar Akçay³, Sonia Kleindorfer^1,2,4

Konrad Lorenz Research Center for Behavior and Cognition, University of Vienna, Grünau im Almtal, Austria
Department of Behavioral and Cognitive Biology, University of Vienna, Vienna, Austria
School of Life Sciences, Anglia Ruskin University, Cambridge, United Kingdom
College of Science and Engineering, Flinders University, Adelaide, South Australia, Australia

*Corresponding author: andrewckatsis@gmail.com

Description of the data and file structure

*Full details for this dataset are given in Katsis et al. (2025,Behavioral Ecology).

Files and variables

File: TerritoryDefense.csv

Description: This file contains the behavioral responses of male Darwin's finches to simulated territory intrusions. Playback trials were conducted in February and March 2024 on Floreana Island. Statistical methods are described in the associated paper by Katsis et al. (2025, Behavioral Ecology).

Variables

TrialID: Unique ID for a single playback trial (combination of nestID and date)
NestID: Unique ID for each nest; nests that are taken over receive a new nestID
NestID_Stage: Combination of nest ID and the breeding stage during which the trial took place
MaleID_Alu: Unique ID for each male nest owner. If banded, the male's aluminium band number is listed; otherwise, the nestID is substituted.
Site: Site at which the nest was located. Cerro Pajas and Asilo de la Paz are both sites in the humid highlands.
Date: Date on which the trial was conducted (YYYY-MM-DD)
Observer: Experimenter who conducted the playback trial (ACK = Andrew C. Katsis, SK = Sonia Kleindorfer)
Time: Time when the playback trial was conducted (24-hour time, Galápagos time)
Species: Species of male nest owner (SGF = small ground finch, CF = cactus finch, STF = small tree finch, MTF = medium tree finch)
PlaybackTrack: Unique ID for the playback track used for the trial
TrialNo: The nth trial conducted for this male (range 1-6), regardless of breeding stage or nestID
TrialNo_Nest: The nth trial conducted for this nest (range 1-6), regardless of breeding stage
BreedingStage: The breeding stage during which the trial was conducted (unpaired male, paired male, incubation, chick feeding)

Baseline_TimeWithin5m: Baseline period: Time (secs) spent within 5 m of the speaker
Baseline_TimeWithin1m: Baseline period: Time (secs) spent within 1 m of the speaker
Baseline_MinDistance: Baseline period: Minimum distance (m) from the speaker
Baseline_Flights: Baseline period: Number of flights
Baseline_Crosses: Baseline period: Number of crosses over the speaker
Baseline_Songs: Baseline period: Number of trill songs produced
Baseline_Whistles: Baseline period: Number of whistles produced
Baseline_Buzzes: Baseline period: Number of buzzes produced (tree finches only)

(Note: "na" in the above columns indicates that baseline behavioral data were not recorded prior to the playback trial.)

Min1_TimeWithin5m: Minute 1: Time (secs) spent within 5 m of the speaker
Min1_TimeWithin1m: Minute 1: Time (secs) spent within 1 m of the speaker
Min1_MinDistance: Minute 1: Minimum distance (m) from the speaker
Min1_Flights: Minute 1: Number of flights
Min1_Crosses: Minute 1: Number of crosses over the speaker
Min1_Songs: Minute 1: Number of trill songs produced
Min1_Whistles: Minute 1: Number of whistles produced
Min1_Buzzes: Minute 1: Number of buzzes produced (tree finches only)

Min2_TimeWithin5m: Minute 2: Time (secs) spent within 5 m of the speaker
Min2_TimeWithin1m: Minute 2: Time (secs) spent within 1 m of the speaker
Min2_MinDistance: Minute 2: Minimum distance (m) from the speaker
Min2_Flights: Minute 2: Number of flights
Min2_Crosses: Minute 2: Number of crosses over the speaker
Min2_Songs: Minute 2: Number of trill songs produced
Min2_Whistles: Minute 2: Number of whistles produced
Min2_Buzzes: Minute 2: Number of buzzes produced (tree finches only)

Min3_TimeWithin5m: Minute 3: Time (secs) spent within 5 m of the speaker
Min3_TimeWithin1m: Minute 3: Time (secs) spent within 1 m of the speaker
Min3_MinDistance: Minute 3: Minimum distance (m) from the speaker
Min3_Flights: Minute 3: Number of flights
Min3_Crosses: Minute 3: Number of crosses over the speaker
Min3_Songs: Minute 3: Number of trill songs produced
Min3_Whistles: Minute 3: Number of whistles produced
Min3_Buzzes: Minute 3: Number of buzzes produced (tree finches only)

HatchingSuccess: (for trials conducted during the incubation stage) whether the nest hatched at least one offspring. Y = at least one offspring hatched, N = no offspring hatched, uk = hatching success unknown due to inadequate monitoring, na = not applicable, indicating that hatching success is not a relevant metric for this nest, either because eggs were not laid or because chicks were already hatched when experiments began.

File: ParentalCare.csv

Description: This file contains parental care data from nest observations of Darwin's finches. Data were collected from January to March 2024 on Floreana Island. Statistical methods are described in the associated paper by Katsis et al. (2025, Behavioral Ecology).

ObservationID: Unique ID for a single one-hour nest observation (combination of nestID and date)
NestID: Unique ID for each nest; nests that are taken over receive a new nestID
NestID_Stage: Combination of nest ID and the breeding stage during which the trial took place
Site: Site at which the nest was located. Cerro Pajas and Asilo de la Paz are both sites in the humid highlands.
Date: Date on which the observation was conducted (YYYY-MM-DD)
Time: Time when the observation was conducted (24-hour time, Galapagos time)

Observation: The nth trial conducted for this nest at each breeding stage
BreedingStage: The breeding stage during which the trial was conducted (incubation or chick feeding)
WithinStage: Estimated within-stage timing of the breeding attempt (early = day 1–7 of incubation or chick feeding, late = day 8–14 of incubation or chick feeding)
Observer: Observer/s who conducted the nest observation (AB = Abbie Hay, ACK = Andrew C. Katsis, AH = Alena Hohl, CL = Calean Linke, JD = Jeff Dawson, JK = Johanna Kniely, KA = Katherine Albán Morales, LH = Leon Hohl, LKC = Lauren K. Common, MK = Melanie Kaluppa, MM = Matt Milham, RD = Rachael Dudaniec, SK = Sonia Kleindorfer, US = Ursula Scuderi)
MaleSpecies: Species of male nest owner (SGF = small ground finch, CF = cactus finch, STF = small tree finch, MTF = medium tree finch). Note that the female nest owner is usually but not necessarily conspecific.
MaleID_Alu: Unique ID for each male nest owner. If banded, the male's aluminium band number is listed; otherwise, the nestID is substituted.

Brood_Inc_Duration: The total duration (in mins) of incubation or brooding across the 60-min observation
MaleFeedsFemale: The number of food deliveries by the male to the female, either during the incubation or chick feeding stage
MaleFeedsChicks: The number of food deliveries by the male to the chicks, during the chick feeding stage
FemaleFeedsChicks: The number of food deliveries by the female to the chicks, during the chick feeding stage

File: SupplementaryDataFile.xlsx

This file contains the same data outlined above in "TerritoryDefense.csv" and "ParentalCare.csv", but in an Excel spreadsheet. The file includes two sheets containing data ("TerritoryDefense" and "ParentalCare") and one sheet containing definitions of every variable ("Key").

File: SupplementaryRCode.txt

This file contains the R code used to prepare and analyse the data used in this study.

File: SupplementaryROutput.html

This file contains the R code used to prepare and analyse the data used in this study, in addition to the output from each analysis (including statistical outputs and figures). This file is formatted using R Markdown.

File: PlaybackTracks.zip

This ZIP file includes all 25 playback tracks (as WAVE files) that were used to conduct our territory defence trials. Each track lasts 3 mins (1 min of song playback, 1 min of silence, 1 min of song playback) and all songs within a track are from the same male individual. Each 1-min song playback period contains six repetitions of the same male song type, simulating a territory intrusion by a single unfamiliar conspecific. We used a high-pass filter to remove sounds < 1 kHz and saved the playback tracks as uncompressed 16-bit WAVE files. Of the 25 playback tracks, N = 8 feature small tree finch song, N = 8 small ground finch song, N = 7 medium tree finch song, and N = 2 common cactus finch song.

Playback tracks:

* CF_Track01.wav
* CF_Track02.wav
* MTF_Track01.wav
* MTF_Track02.wav
* MTF_Track03.wav
* MTF_Track04.wav
* MTF_Track05.wav
* MTF_Track06.wav
* MTF_Track08.wav
* SGF_Track01.wav
* SGF_Track02.wav
* SGF_Track03.wav
* SGF_Track04.wav
* SGF_Track05.wav
* SGF_Track06.wav
* SGF_Track07.wav
* SGF_Track08.wav
* STF_Track01.wav
* STF_Track02.wav
* STF_Track03.wav
* STF_Track04.wav
* STF_Track05.wav
* STF_Track06.wav
* STF_Track07.wav
* STF_Track08.wav

This ZIP file also includes "PlaybackTracksDetails.csv", a summary of each playback track and the individuals whose songs were used to construct them. The variables in this spreadsheet are defined below:

PlaybackTrack: Unique ID for each playback track that was used in our territory defense experiment
Recorder: The experimenter who recorded the Darwin's finch song (Çağlar Akçay, Alper Yelimlieş, or Sonia Kleindorfer)
Date: The date on which the songs were recorded
Species: The Darwin's finch species that features in the recording
ScientificName: The scientific name of the Darwin's finch species that features in the recording
Sex: The sex of the individual featured in this recording (always male in this dataset, as only male Darwin's finches sing)
Age: The life stage of the individual featured in this recording (adult, juvenile, or unknown). Adults are 1+ years old.
PlumageColour: The plumage colour of the individual featured in this recording, ranging from B0 (approximately 1 year old) to B5 (approximately 6+ years old). Male body color (in ground finches) or head color (in tree finches) darkens during their first six years.
GeographicalArea: All recordings took place in the Galápagos Islands.
Island: All recordings took place on Floreana Island.
Site: The site where the individual was recorded. "Lowlands" is the lowland area in and around the township of Puerto Velasco Ibarra. "Cerro Pajas", "Asilo de la Paz", "Asilo Track", and "Post Office Bay Trail" are all located in the highlands.
RecordingGear: The recorder used to create this recording (Marantz PMD 660 or Zoom H5)
Microphone: The microphone used to create this recording (Sennheiser ME67/K6 or Sennheiser MKE600)

Version changes

2025-09-22: Added ZIP file "PlaybackTracks.zip", which contains all 25 playback tracks (as WAVE files) that were used to conduct our territory defence trials. This ZIP file also contains a spreadsheet summary of each playback track and the individuals whose songs were used to construct them.

Study sites and species

We conducted our study from January to March 2024 on Floreana Island in the Galápagos archipelago, at two highland (humid zone) sites and one lowland (dry zone) site. The two highland sites, located at Asilo de la Paz (1°18’46” S 90°27’16 ”W) and the base of Cerro Pajas (1°17’46” S 90°27’06” W), consisted largely of remnant Scalesia pedunculata forest. The one lowland (dry zone) site comprised dry scrubland dominated by palo santo trees (Bursera graveolens) in and around the township of Puerto Velasco Ibarra (1°16’28” S 90°29’13” W). Our study included four of the five Darwin’s finch species considered extant on the island: the small ground finch (Geospiza fuliginosa), common cactus finch (Geospiza scandens), small tree finch (Camarhynchus parvulus), and medium tree finch (Camarhynchus pauper). Small ground finches and small tree finches were present at all three sites, medium tree finches only breed at the two highland sites, and cactus finches only at the lowland site. We did not identify any nests belonging to the island’s fifth extant species, the medium ground finch (Geospiza fortis).

Nest monitoring

We searched for Darwin’s finch nests at our three study sites and monitored the breeding activity of male finches whose territory defense behavior we had previously measured. Upon discovering an active display nest, we observed the male for ~20 min to determine if he was paired or unpaired. We then revisited the nest approximately every three days to confirm the male’s current status. If the male became paired, we continued to regularly monitor the breeding pair to determine the success of their nesting attempt. To establish the breeding stage (incubation or chick feeding), we either used a borescope to visually confirm the presence of eggs or nestlings or observed the parents’ incubation or provisioning behavior with binoculars, following a standardized protocol. When observing parental behavior, the observer was seated on the ground, approximately 10 m from the nest, with binoculars focused on the nest entrance. As Darwin’s finches do not noticeably alter their behavior in the presence of a human observer within 5 m, this observer distance was unlikely to disrupt parental behavior. All nest observations took place in the morning, between 06:00 and 12:00 GALT, to minimize time-of-day effects.

Territory defense trials

Our playback stimuli were constructed from Darwin’s finch songs recorded on Floreana Island in 2023. We created 25 unique playback tracks (8 small ground finch, 8 small tree finch, 7 medium tree finch, 2 cactus finch), each lasting 3 min (1 min of song playback, 1 min of silence, 1 min of song playback). Each 1-minute song playback period contained six repetitions of the same male song type, simulating a territory intrusion by a single unfamiliar conspecific.

Upon entering a Darwin’s finch territory, we placed the speaker in the branches of a shrub or tree about 5 m from the nest, at a height of 1–1.5 m. Playback tracks were randomly assigned to each subject, with the provision that each male received a conspecific song. We never started playback until the male was observed within 20 m of the speaker; in cases where the male was unbanded, we waited until he returned to the nest or interacted with the female to ensure we were observing the nest owner. After playback began, an observer (ACK or SK) narrated the male’s response into a digital audio recorder. For each trial, we quantified six response variables during the playback period: time (in secs) within 5 m of the speaker, time (in secs) within 1 m of the speaker, minimum distance (in m) from the speaker, number of flights, number of crosses (flights that crossed the speaker), and number of vocalizations (defined in Table 1). For a subset of trials (N = 24 of 168 trials), we also recorded the male’s behavior during a 1-minute baseline period prior to the beginning of playback.

Across 168 playback trials, we tested males at 98 nests (37 small ground finch, 28 medium tree finch, 27 small tree finch, 6 cactus finch). Of these, two small ground finch nests belonged to the same color-banded male over two consecutive breeding attempts. Territory defense trials were conducted across four stages of the breeding cycle: unpaired (male was unpaired and defending a display nest), paired (male was paired with a female), incubation (female was incubating eggs), and chick feeding (male and female were feeding chicks).

Parental care observations

During incubation and chick feeding, we conducted 1-hour parental care observations at Darwin’s finch nests between 06:00 and 12:00 GALT, following long-term standardized protocols for this study population. Observers were positioned about 10 m from the nest with binoculars focused on the nest entrance. During the incubation stage, we recorded: (1) the number of male food deliveries to the incubating female at or near the nest entrance, and (2) the total female incubation time (mins). During the chick feeding stage, we recorded: (3) number of male food deliveries to the chicks or females; and (4) total female brooding time (mins). In total, we conducted 113 parental care observations at 59 nests (24 small ground finch, 18 small tree finch, 15 medium tree finch, 2 cactus finch). For each observation, we estimated the within-stage timing of the breeding attempt based on our timeline of monitoring records. Given our monitoring schedule, this estimate was usually considered precise to within 3 days. Using this estimate, we then broadly assigned each protocol to the early (day 1–7) or late (day 8–14) stage of incubation or chick feeding.