# Leaf Nests of Gray Squirrel in Connecticut

> That ball of leaves high in a tree is a squirrel’s summer home, and in 1941 two researchers in Connecticut pulled down 146 of them to see how they are built. They found nests mostly in white pines, lined with moss, grass and shredded bark, woven from oak leaves carried in from other trees, and busy with fleas, caterpillars and leftover meals. They also describe how to tell a nest in use from an old one.

Summary by Kersey Lawrence, Original Wisdom. Updated 9 November 2026. Page: https://www.originalwisdom.com/tracking-literature/1944-fitzwater-jr-leaf-nests-gray-squirrel/

## Citation and access

- **Authors:** William D. Fitzwater, Jr. and William J. Frank
- **Year published:** 1944
- **Journal or source:** Journal of Mammalogy
- **Full citation:** Fitzwater, W. D., Jr. and Frank, W. J. 1944. Leaf nests of gray squirrel in Connecticut. Journal of Mammalogy 25(2): 160-169.
- **DOI:** 10.2307/1375016
- **Access status:** Publisher link only
- **Where to find it:** https://doi.org/10.2307/1375016

## Tags

- **Species:** Mammals > Eastern grey squirrel
- **Region:** North America > United States
- **Tracking:** Feeding signs; Hair; Sign surveys; Tracking; Tracks and signs identification
- **Behaviour and ecology:** Behaviour; Feeding; Nesting
- **Methods and technology:** Descriptive statistics
- **Data type:** New field data
- **Observer qualification:** Not reported
- **Discipline:** Behaviour and ecology; Wildlife tracking
- **Year published:** 1944

## Detailed keywords

- **Species:** Studied: gray squirrel (Sciurus carolinensis leucotis), through its leaf nests. Nest trees: white pine (Pinus strobus), red maple (Acer rubrum), gray birch (Betula populifolia), hemlock (given in the paper as Taxus canadensis), white oak (Quercus alba), black birch (Betula lenta), yellow birch (Betula lutea), apple (Pyrus malus), red oak (Quercus spp.), black cherry (Prunus serotina), white ash (Fraxinus americana), white elm (Ulmus americana) and sugar maple (Acer saccharum). Nest materials: 39 kinds of vegetation, led by the oaks, white pine, red maple, mosses (Polytrichum commune, Calliergon cordifolium, Heterophyllium halanianum, Sphagnum spp.), sugar maple, grasses, birches, ground pine (Lycopodium complanatum) and chestnut (Castanea dentata), plus shredded bark. Food remains in nests: gnawed bones, cherry pits, red and white oak acorns and husks, pine cones and skunk cabbage seeds. Also found in nests: ruffed grouse feathers, feathers believed to be from a slate-colored junco, fleas (Megabothris), larvae, pupae and adults of 18 insect families, spiders, centipedes and free-living nematodes. Other squirrels discussed from the literature only: fox squirrel, western gray squirrel, red squirrel and flying squirrel (Glaucomys sabrinus).
- **Location and habitat:** Litchfield-Morris Wildlife Sanctuary (about 4,000 acres), between the villages of Bantam, Litchfield and Morris, west-central Connecticut, United States. About 95% forested with second-growth hardwoods, old field white pines and conifer plantations (red pine, white spruce and Scotch pine), with red maple and elm swamps; a former farming area. Study tract one-half mile wide and one and a half miles long.
- **Topics:** leaf nests (dreys) versus tree dens; nest tree selection; nest height in relation to tree height; nest structure and building plans; nest materials; telling active from old nests by green vegetation, a dry inner chamber, hair and fleas; one nest per squirrel and nest-based population census; sanitation and parasites as a reason for new nests; young born in or moved to leaf nests; food remains in nests; insects and other invertebrates living in nests.
- **Statistics or models:** Descriptive statistics only: counts, percentages, averages, minimums and maximums. Inconsistencies in the paper: (1) hemlock is given the scientific name Taxus canadensis (the name of Canada yew) in Tables 1 and 3; (2) Table 1 gives white oak as 57.0% active, while 4 of 7 nests is 57.1%; (3) the active share is given as 45 percent and as 45.2 percent (66 of 146); (4) fleas are reported in 60 percent of active nests on page 162 and summary, but in “60 percent of the nests” on page 168; (5) American elm appears in Table 3 (4%) and again in the list of species found only once.
- **Data type:** New field data: 146 leaf nests examined in the fall of 1941 (70 of them analysed for nest materials, 58 active and 12 inactive but in good condition). A week-old litter was found in a leaf nest on March 12, 1942.

## Synopsis

### 1. What they did

Gray squirrels live in two kinds of shelter: dens in tree hollows, and leaf nests built out in the branches. Little had been written about leaf nests, so while a nest-based census of gray squirrels was being tried on the Litchfield-Morris Wildlife Sanctuary in Connecticut, the authors studied the nests themselves in detail.

In the fall of 1941 they walked parallel lines one eighth of a mile apart across a tract half a mile wide and one and a half miles long. For every nest they recorded:

- The tree: forest type, tree species, trunk diameter at breast height and estimated tree height.

- The nest’s position: height above the ground, and where it sat in the tree, usually with a sketch.

- The nest itself: outside length, width and depth, and the size of the inner chamber.

- Its contents: each nest was taken down in an old sheet, weighed and pulled apart to measure its materials and twigs, and to note food remains, hair and insects.

They also judged whether each nest was in use that season or left over from an earlier one.

### 2. What they found

Active or old?

- A nest with mostly green material and a dry inner chamber was clearly in use. Nests built earlier in the season were harder to judge, so the authors also used hair, which they found an excellent guide to which species was using a nest and which seemed present only in recent nests, and fleas, which live about 100 days after feeding.

- 66 of the 146 nests (45%) were judged active, and 60% of the active nests had fleas.

Nest trees

- The 146 nests were in 13 tree species, and five species held 83.7% of them.

- White pine held 79 nests (54.1%), even though the area is mostly hardwood forest; white pine and hemlock together held 59.6%. Nearly half of the white pine nests were in lone pines among hardwoods, and there were no nests in red pine, Scotch pine or white spruce plantations. The authors note this seems contrary to the popular belief that gray squirrels favour hardwood stands.

- Red oak, white oak, black birch and yellow birch were the only species with more than half their nests active. Gray birch had many nests, but only 30.8% active, perhaps because old nests are easy to see in their open crowns.

- The smallest nest trees were 15 cm across and 8 m tall. The average nest tree was 35 cm across and 17 m tall, so the squirrels chose good-sized trees.

- Nests averaged 11.1 m above the ground (3.5 to 22.0 m). Taller trees had higher nests: nests sat at the base of the crown in large trees and well up into the top of small ones.

The nests

- Nests were built in the top fork of small hardwoods or close to the trunk on a main branch of larger trees; only 3.4% were out on side branches.

- They were roughly round, on average 35 by 45 cm and 30 cm high, and weighed 1300 g on average (450 to 4450 g). The inner chamber averaged 12 by 15 by 9 cm.

- There was usually one well-hidden entrance, most often facing the trunk or the nearest limb that gave a good runway, and the chamber lay a few centimetres below it.

- Each nest had three or four parts: a platform of twigs, usually from the nest tree; a packed base of decaying material; an outer shell of leaves and twigs; and, in over 75% of nests, a separate inner shell of shredded bark, grass or leaves.

- There were three building plans: freshly cut leafy twigs packed into a crotch (typical of hardwoods, especially birches); single leaves or short leafy twigs woven into a loose framework of twigs (common in pines, using oak leaves); and, least often, a mound of grass, bark, sphagnum moss or similar material placed on a platform and burrowed into.

Nest materials

- 39 kinds of vegetation were found in the 70 nests examined for materials, up to 14 in one nest (6 on average).

- Oak leaves were used most: white oak in 71% of nests and red oak in 70%, although oaks were only 7.5% of nest trees. Mosses, grasses, sedges and shredded bark lined the inner chamber.

- Only 8.6% of nests were built entirely from the nest tree, and 60% mostly from it, so squirrels did not take all their materials from the tree they built in.

- The support twigs averaged 300 g (23% of nest weight), 4 mm across at the butt and 40 cm long.

- Bird feathers, and paper and cloth torn from a “No Hunting” sign, were also found.

Food and other life in the nests

- Food remains were common: gnawed bones, cherry pits, acorns and husks, pine cones and skunk cabbage seeds. 20% of nests held skunk cabbage seeds and 26% held white oak acorns or husks.

- Insects were abundant, from 18 families, with two moth families (Noctuidae and Pyralididae) the most common, along with spiders, centipedes and nematodes. Wood-boring beetles may have arrived with shredded bark. Some nests built that season had been so eaten away by caterpillars that they were damp and unusable.

Number of nests and young

The authors found one nest per tree, sometimes with new nests built on old ones, and a nest census based on one nest per squirrel gave reasonable results. A week-old litter was found in a leaf nest in March 1942.

### 3. What they concluded

- Leaf nests are important in the gray squirrel’s life: they provide enough shelters, and clean quarters close to food.

- The authors suggest squirrels build leaf nests because there are not enough dens when they spread out in spring, for cleanliness away from droppings and parasites, and to live near their main food.

- White pine was the most important nest tree on this area, and squirrels preferred good-sized trees.

- Contrary to earlier accounts, nest materials are not necessarily taken from the nest tree or the nearest species.

- Connecticut nests were consistently larger than leaf nests measured in Ohio.

- The relationship between the squirrels and the insects in their nests would make an interesting study, and the nests may offer a ready supply of animal food.

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

The study is a survey of one kind of animal sign, the leaf nest. Nests were found along parallel survey lines, and the authors read signs at and in each nest to judge whether it was in use: green material, a dry chamber, hair (as a guide to which species used it) and live fleas. Food remains in the nests (gnawed bones, acorn husks, cherry pits, cones and skunk cabbage seeds) were read as signs of feeding. No trailing was reported.

### 5. Tracker or observer certification

Not reported. The authors did the fieldwork themselves and say openly that some nests were borderline cases when judging whether they were active.

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

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

- The paper gives trackers practical clues for telling a current squirrel nest from an old one: green leaves, a dry inner chamber, fresh hair and fleas, while old nests lose their greenness and are eaten away by insects.

- Where a nest sits can help with age and visibility: nests in open-crowned trees such as gray birch are easy to see, so old nests may be over-counted there compared with denser trees.

## Cite this summary

Lawrence, K. 2026. Summary of: Leaf Nests of Gray Squirrel in Connecticut (Fitzwater and Jr. et al., 1944). Original Wisdom, Tracking Literature. https://www.originalwisdom.com/tracking-literature/1944-fitzwater-jr-leaf-nests-gray-squirrel/