# Use of faecal pellet size to differentiate age classes in female Svalbard reindeer Rangifer tarandus platyrhynchus

> Can a handful of droppings tell you how old a reindeer is? Measuring the pellets of marked female Svalbard reindeer on Svalbard, Norway, researchers found that combining length, width and depth sorted calves, yearlings and adults correctly about 91% of the time, while any single measurement was much less reliable. They suggest pellet measurements, paired with DNA to tell males from females, could become a cheap, hands-off way to read the age structure of wild herds.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/2011-morden-weladji-use-faecal-pellet-size/

## Citation and access

- **Authors:** C-Jae C. Morden, Robert B. Weladji, Erik Ropstad, Ellen Dahl and Øystein Holand
- **Year published:** 2011
- **Journal or source:** Wildlife Biology
- **Full citation:** Morden, C-J. C., Weladji, R. B., Ropstad, E., Dahl, E. and Holand, Ø. 2011. Use of faecal pellet size to differentiate age classes in female Svalbard reindeer Rangifer tarandus platyrhynchus. Wildlife Biology 17(4): 441-448.
- **DOI:** 10.2981/10-023
- **Access status:** Hosted (freely available elsewhere)
- **PDF:** https://www.originalwisdom.com/wp-content/uploads/2026/11/2011_Morden_and_Weladji_etal_use-of-faecal-pellet-size-to-differentiate-age-classes-in-female-svalbard-reindeer.pdf

## Tags

- **Species:** Mammals > Reindeer
- **Region:** Europe > Norway
- **Tracking:** Scat; Tracking; Tracks and signs identification
- **Data type:** New field data
- **Observer qualification:** Not needed
- **Discipline:** Wildlife tracking
- **Year published:** 2011

## Detailed keywords

- **Species:** Studied: Svalbard reindeer (Rangifer tarandus platyrhynchus), females only (calves, yearlings and adults). Other species discussed from earlier studies: caribou (Rangifer tarandus), Manipur brow-antlered deer (Cervus eldi eldi), elk (Cervus elaphus), moose (Alces alces), mule deer (Odocoileus hemionus), greater bilby (Macrotis lagotis), Sumatran elephant (Elephas maximus sumatranus), roe deer (Capreolus capreolus), European rabbit (Oryctolagus cuniculus), Reeves’ muntjac (Muntiacus reevesi) and leporids (hares and rabbits).
- **Location and habitat:** Nordenskiøldland, Spitsbergen, Svalbard, Norway (77°50’-78°20’N, 15°00’-17°30’E), including Colesdalen, Semmeldalen and parts of Reindalen, with adjacent side valleys. In winter the reindeer feed on mosses and low-quality vascular plants. About 1,500 wild reindeer, rare human presence and few predators.
- **Topics:** faecal pellet morphometry (pellet length, width, depth and a volume index); age class identification from scat; non-invasive population monitoring; population age structure and recruitment; pellet size and live body mass; model validation with a second year of data; seasonal (month) effects on pellet size; need to know the sex of the animal (for example by DNA) before applying the method; effects of freezing, drying and pellet age as open questions. Possible inconsistencies in the paper: the abstract and discussion give 91% correct classification for the length, width and depth combination, the results give 90.7%; the discriminant analysis found length and width the best overall model (error 24.4%) and length, width and depth intermediate (error 25.7%), while the validation favoured length, width and depth (91% against 86% for length and width); in Table 3 the predictor in the volume model is labelled “Live weight” instead of volume, and the width standard error reads 3.2858 in the text and 3.285 in the table; the discussion says calves were “nearly 20 kg” lighter than adults, while the reported means (29.17 kg and 49.50 kg) differ by just over 20 kg.
- **Statistics or models:** Generalised linear mixed models (SAS PROC MIXED) with individual as a random factor; linear mixed models of body mass by age class (least square means); linear mixed models of live weight against pellet dimensions, controlling for age class, year and month; multiple discriminant analysis (SAS PROC DISCRIM); cross-validation and validation with the 2009 data; running mean approach to choose sample size (five pellets per animal); random subset of calves drawn in Minitab 15.0; significance level 5%.
- **Data type:** New field data: faecal samples from known-age, marked female reindeer collected in February and April 2008 (158 pellet groups) and 2009 (161 pellet groups), from a population monitored since 1994.

## Synopsis

### 1. What they did

Knowing the age structure of a population helps managers follow recruitment, growth and mortality. Finding it out usually means catching, weighing or even killing animals, which is costly and stressful for them. The authors asked whether the size of faecal pellets could tell apart female Svalbard reindeer of different ages without handling them.

The Svalbard reindeer in Nordenskiøldland, Spitsbergen, have been studied since 1994, and many females carry ear tags and neck collars, so their ages are known.

- Collecting the samples. During four visits in February and April of 2008 and 2009, the team collected 319 pellet groups from 272 known females (1,834 pellets): 263 groups from adults, 25 from yearlings and 31 from calves. Faeces were taken directly from the animal or picked up from the snow straight after the animal defecated, then kept frozen.

- Measuring the pellets. Five complete, regular oval pellets per animal were measured with Vernier calipers for maximum length, maximum width and depth (measured at a right angle to the width). Length times width times depth gave a volume index. One person measured every sample.

- Comparing age classes. They compared pellet size between calves (under 1 year), yearlings (1 to 2 years) and adults (2 years and over) using the 2008 data and a random set of 20 calves. Severe icing in the winter of 2008 killed many calves, so the 2009 samples had no calves and very few yearlings.

- Testing how well pellets classify age. They built models from single measurements and combinations of measurements, then checked them with the 2009 data and the remaining 11 calves. They also ran a discriminant analysis, a method that sorts samples into groups from several measurements at once.

- Linking pellets to body mass. They compared body mass between age classes and tested whether heavier females produced larger pellets.

### 2. What they found

Pellet size by age

- Adults had the largest pellets on every measurement, yearlings were in between, and calves had the smallest.

- Adult pellets were longer than calf pellets, but length did not differ between adults and yearlings, or between yearlings and calves.

- Adult and yearling pellets were wider than calf pellets, and adult pellets were wider than yearling pellets.

- Adult pellets were deeper and larger in volume than both calf and yearling pellets; calf and yearling pellets did not differ in depth or volume.

- Pellets collected in February were wider, deeper and larger in volume than those collected in April.

How well pellets told ages apart

- A single measurement classified 56.4% (length alone) to 79.1% (width or depth alone) of pellet groups into the right age class.

- Length and depth together classified 89% correctly. Length, width and depth together did best, at 90.7% (91% in the abstract and discussion).

- In the discriminant analysis, length and width together gave the lowest overall error (24.4%); length, width and depth gave 25.7%. Both models placed 80.7% of calf pellet groups correctly. About 19% of adult pellet groups were classified as yearlings.

- When checked against the second year of data, the length and width model classified 86% correctly, against 91% for length, width and depth.

Body mass

- Calves weighed on average 29.2 kg, yearlings 38.6 kg and adults 49.5 kg.

- Heavier females produced wider, deeper and larger pellets. Pellet length was not linked to body mass.

### 3. What they concluded

- One pellet measurement alone was not enough to separate age classes. A combination of maximum length, maximum width and depth gave a good basis for separating calves, yearlings and adults among female Svalbard reindeer.

- Adults were easier to separate from the other two classes, because calf and yearling pellets were more variable in size.

- The method only works if the sex of the animal that left the pellets is known. Reindeer males and females differ in size, so a pellet from a yearling male could be mistaken for one from an adult female. In the field, pellets would normally need to be combined with a technique such as DNA analysis to tell the sexes apart.

- The same approach could probably be applied to other reindeer and caribou populations, other hoofed mammals and other animals that produce pellets.

- Future work should look at how season, diet, insects, weather, freezing, drying and the age of the pellet affect pellet size.

### 4. How tracking was or was not used

No tracking in the field was involved: every sample came from a known, marked female, taken straight from the animal or picked up from the snow just after the animal defecated. The study is about reading one kind of sign, scat, to learn the age class of the animal that left it. It measured the size and shape of reindeer pellets as a possible way to judge age from droppings found in the field.

### 6. Other technologies, skills or innovations

- Vernier calipers with a precision of 0.05 cm for measuring each pellet.

- A running mean approach to decide how many pellets to measure per animal (five).

- Validation of the models with a second, independent year of data from the same population.

- Long-term marking of the population (ear tags and neck collars) so that the age of each sampled female was known.

### 7. Implications for conservation (from the paper)

- Pellet measurements could offer a cheap, non-invasive way to learn the age structure of wild populations, including recruitment, without capturing, handling or killing animals.

- Combined with DNA and hormone techniques, pellet size and age data may improve the non-invasive monitoring of wild reindeer and perhaps other hoofed mammals.

- Faecal data may help with rare or secretive species, where direct counts are difficult.

### 8. Implications for tracking (Original Wisdom's observations)

_These are Original Wisdom's observations, not the authors'._

- Trackers often judge whether droppings come from a young or an adult animal by their size. This study puts numbers on that judgement for one population: a combination of length, width and depth sorted 91% of female reindeer pellet groups correctly in the validation, while length alone sorted only 56.4% correctly.

- The overlap between age classes, and between the sexes, is a reminder that pellet size on its own is a guide rather than a certainty, especially for young animals.

- Pellets collected in February were wider, deeper and larger than those collected in April, so the time of year may matter when comparing droppings.

## Cite this summary

Lawrence, K. 2026. Summary of: Use of faecal pellet size to differentiate age classes in female Svalbard reindeer Rangifer tarandus platyrhynchus (Morden and Weladji et al., 2011). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/2011-morden-weladji-use-faecal-pellet-size/