Female · island plateau
- Measurement rows
- 9
- Years with a row
- 8
- First record
- 2008
- Last record
- 2021
Field labels let repeated measurements stay connected. They do not tell us what happened between captures.
Seen Again
Follow the same tortoises through years of field measurements.
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How to explore
Researchers marked Hermann's tortoises on Golem Grad island and the nearby mainland, then recorded measurements when they found the animals again. A blank year means there is no row, not that the animal died or left.
Start with P-129
Follow one island female through nine measurement rows, then switch the measurement shown.
Compare one year
Press a point or move the year slider to place that record among other rows from the same field group.
Scan repeated sightings
Choose a filled square to follow another tortoise recorded across several years.
Read the clutch rows
Select a point to compare observed egg count, body mass, place, and date.
- Marked tortoise
- An animal given a field label so measurements from later captures can be linked to the same individual.
- Measurement row
- One recorded capture with body mass, straight shell length, year, season, place, and recorded sex.
- Straight shell length
- The shell length measured in a straight line and reported here in millimetres.
- Mass-to-length ratio
- Body mass in grams divided by straight shell length in millimetres; the ratio alone is not a health diagnosis.
- Clutch row
- One observation of a marked female with the number of eggs recorded on that date.
Hermann's tortoise field records · 2008–2025Seen
Seen
again
Follow the same tortoises through years of field measurements.
Researchers marked tortoises on Golem Grad island and the nearby mainland in North Macedonia. Each row records one capture. The gaps between rows are unknown time, not proof that an animal left or died.
Follow one field label
Choose a place, sex, and marked tortoise. Each point is one measurement. Change the measure to see mass, shell length, or their ratio.
Mass-to-length ratio6.80 g/mm median for P-129
Press a point to carry its year into the next view. Two points in one year mean the animal was measured twice.
7.04 g/mm6.23 g/mm
Spring rowSummer row
How to read it: height shows the chosen measurement, while horizontal position shows the year. A line through gaps would imply measurements the researchers did not make, so the points remain separate.
Put that year in context
Compare P-129 with other female tortoises measured at the island plateau. A taller bar means more measurement rows in that range.
2021 · Plateau femalesMass-to-length ratio distribution
Spring and summer rows
4.0
1
5.0
3
45.9
3
56.9
1
7.8
g/mm
What changed: the year and season controls change which rows enter the bars. The same field group and measurement stay selected, so the comparison remains consistent.
Scan the field notebook
These 14 tortoises have rows in the most years for the selected field group. Press a filled square to follow that tortoise and compare that year.
Compare observed egg counts
The separate clutch file contains 53 records from 46 marked females. Horizontal position shows body mass at the record; vertical position shows eggs counted.
Eggs countedBody mass · grams135791150010001500200025003000
PlateauBeachKonjsko
Six females with more than one clutch row
The same female can have a different count in another year.
How to read it: the records show observed clutches, not every clutch laid. The sample is small and uneven across places: 9 plateau rows, 13 beach rows, and 31 mainland rows. The chart describes these records; it does not by itself prove what caused the differences.
Keep the record honest
A blank year is not an ending.
Capture records depend on where researchers looked, which tortoises they found, and when fieldwork occurred. The large differences in row counts among places and sexes are not direct population counts.
Data limits and transformation
The page retains all 10,174 source measurement rows and all 53 clutch rows. “Mass-to-length ratio” is body mass in grams divided by straight shell length in millimetres, the same arithmetic stored as the source's body-condition index. A ratio can vary with body size, season, hydration, reproductive state, and measurement conditions; this project does not treat it as a stand-alone health diagnosis. Source authors used separate capture-probability and survival models for their paper. Those model outputs are outside this descriptive interface.
Why this exists
The question
What can repeated field measurements show about when the same marked Hermann's tortoises were recorded, how their measurements varied, and how the small set of observed clutch counts differed among two island sites and a nearby mainland site?
What to try
Start with island female P-129, switch among marked tortoises and measurements, carry a selected year into the group distribution, choose another individual from the repeated-sighting grid, and compare all 53 clutch records by body mass and place.
Method and limits
About the data
I discovered the source through TidyTuesday's March 3, 2026 Golem Grad tortoise entry, pinned to commit `0706401f24434e48974faa77802c802a947543ca`. I then used the study authors' original Figshare files rather than relying on the curated copies. Figshare identifies Dragan Arsovski, Xavier Bonnet, Ana Golubović, and Ljiljana Tomovic as the authors, provides the persistent DOI `10.6084/m9.figshare.30752687.v1`, and licenses the record, datasets, and code under CC BY 4.0. The related paper is `10.1111/ele.70296` in *Ecology Letters*.
I retrieved Figshare file 60004889, `body_condition.csv`, and file 60004874, `clutch_size.csv`, on October 10, 2026. The first file is 924,801 bytes with SHA-256 `cf5ff607222477bea0f29a1403cdc19a5628263de12c9e42b99e392b99e22777`; the second is 1,764 bytes with SHA-256 `3a6e63f1c7114c309daa8881979c26796a04871803f1f4c950d9be1273623ee7`. Both original files are checked in beside the reducer so the transformation can be repeated if the source disappears.
The standard-library Python reducer verifies both file sizes, hashes, labels, and row counts before writing the static snapshot. It retains all 10,174 measurement rows from 2008–2023 and all 53 clutch rows from 2022–2025. It converts the clutch file's Excel dates to ISO dates and adds the `k` prefix used by the measurement file to matching Konjsko field labels. Repeated reductions produced the same 372,344-byte JSON with SHA-256 `52cfaf0be319f61ab3ccefc853fcdf1e6ce2ddca20aa0ce53da6f1702707e0b1`. The page imports that file and makes no runtime request.
The interface calls the source's body-condition index a mass-to-length ratio because the stored value is body mass in grams divided by straight shell length in millimetres. It describes the arithmetic without treating the ratio as a stand-alone health measure. Group distributions count measurement rows, so an animal recorded twice in the selected slice appears twice. The repeated-sighting grid counts years with at least one row, not survival or continuous presence. The clutch view shows observed rows and medians without fitting a causal model.
Capture records depend on field effort, place, season, detection, and which animals entered the marked sample. Row counts differ sharply among places and recorded sexes and are not direct population counts. A missing year cannot establish death, departure, or reproductive failure. The clutch sample is small and uneven: 9 plateau rows, 13 beach rows, and 31 mainland rows. Body size, season, reproductive state, hydration, measurement conditions, and other factors may affect the measurements. The source authors used separate capture-probability, survival, and population models for the paper; this project does not reproduce those models or use descriptive rows to make causal claims.
Skills used
- Data analysis
- Data engineering
- Statistical reasoning
- Visualization
- Information design
- Interaction design
- Visual design
- Creative coding
- Product thinking
- Editorial storytelling
- Accessibility
- Performance
What the data shows
- The measurement file contains 10,174 rows for 2,139 marked tortoises from 2008–2023. Of those animals, 599 have a row in only one year, while five have rows in 14 different years. Neither pattern alone establishes survival or absence.
- P-129 has nine measurement rows across eight years from 2008–2021. Its mass-to-length values range from 6.23 to 7.04 grams per millimetre. The separate clutch file records two eggs in 2024 and four in 2025 for the same field label.
- For female measurement rows, the median mass-to-length ratio is 8.08 grams per millimetre at Konjsko, 6.27 on the island plateau, and 6.08 on the island beach. These are descriptive row medians from uneven samples, not adjusted population estimates.
- The 53 clutch rows cover 46 marked females. Konjsko's 31 rows have a median of six eggs, the plateau's nine rows a median of four, and the beach's 13 rows a median of three. The small, uneven sample cannot by itself establish why the observed counts differ.