Synanthropes at a Horse Stable in Northern California

Caitlin Dempsey


Synanthropes are wild animals that benefit from human infrastructure. In urban settings, pigeon and rats are widely recognized synanthropes. The word synanthrope is from the Greek words  syn and anthropos which combined mean “together with man”. Synanthropes live near, find food, shelter, and breed in and around human structures.

The horse stable is one such environment that certain species of mammals and birds take advantage of. Horse stalls provide a sheltered environment for building nests and homes both inside and under the structures. Access to grains and water troughs also offers a constant source of food and water.

A brown and light colored finch stands on the back of a horse with light brown fur.
A horse provides a vantage point for this female house finch. Photo: Caitlin Dempsey.

This Northern California horse barn nestled among the chaparral and temperate forests is host to several wild animals and bird species that have adapted to co-exist with the humans and horses at the stables. Related: Scurry zones in Northern California

Here’s look at several of these synanthropes and how they live and thrive among the stables.

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California ground squirrels

California ground squirrels (Otospermophilus beecheyi) were named after Frederick William Beechey who explored Northern California between 1826 and 1828.

These ground squirrels are found in all corners of this stable. California ground squirrels maintain a very small territory, never moving more than 100-150 feet away from their burrows.

Otospermophilus is Greek for “seed loving”. These ground squirrels eat fruits, seeds and vegetables. Squirrels can be seen eating generously from horse feed bins and running off with carrots.

Plenty of places to dig burrows

The soils in this area of the Santa Cruz mountains have a surface layer of well-drained loam. California ground squirrels dig their own burrows that form a connected network of tunnels under the horse stalls.

These burrows provide a cool and moist environment where the squirrels sleep, store food, and raise their young. Multiple tunnels to the surface provide pathways to escape any predators that may enter the burrows. The openings to these burrows are open found just outside the horse stalls.

A California ground squirrel peering out of the opening of a burrow surrounded by a plant and bare ground.  The red wooden side of a horse stall is in the background.
A California ground squirrel sits in the opening of its burrow in front of a horse stall. Photo: Caitlin Dempsey.

A constant source of food

All around the stables, California ground squirrels can be seen grazing. In addition to eating nearby native vegetation, the eggs of ground nesting birds, and insects, these rodents take advantage of a constant supply of horse grain.

The black nuzzle and one white hoof of a large horse eating from a black grain bin.  A ground squirrel has its front paws up on the top edge of the grain bin.
California ground squirrels can frequently be seen eating from the food bins of the horses. Photo: Caitlin Dempsey.

Ground squirrels will frequently dive into the horse troughs to eat barley, wheat, and other seeds and grains put out for the horses. When possible, ground squirrels will also run off with large carrots clenched in their mouths that they find in the stalls.

Grounds squirrels can be seen scavenging for seeds and grain all around the stables.

A baby squirrel sitting up eating in front of a burrow.  The ground is littered with hay.
A juvenile ground squirrel eating grain near a horse stall. Photo: Caitlin Dempsey.

Places to relax and view from

Stumps, fences, and rooftops offer plenty of places for the California ground squirrels to watch over their territories from and to warn other squirrels about dangers.

A ground squirrel sitting on the top of an old wooden post.
The old wooden post provides a California ground squirrel with a viewing place. Photo: Caitlin Dempsey.

California grounds squirrels enjoy sunbathing and resting just outside their burrows. At the sign of any danger, they can quickly dive back into their tunnels for safety.

A ground squirrel sitting on a rock facing a red wooden wall of a stall.
This California ground squirrel is enjoying the sun on a rock outside of a horse stall. Photo: Caitlin Dempsey.

Brewer’s Blackbirds

Along with the California ground squirrels, Brewer’s blackbirds are the most visible synanthropes at the horse stables. These year-round birds gather in large flocks and are comfortable being in close proximity to both horses and people.

A blackbird sitting on a metal railing.  The blurry image of the front part of a horse can be seen in the background.
A Brewer’s blackbird sitting on the railing of a horse arena. Photo: Caitlin Dempsey.

Access to food is made simple by horse feed in open bins. A steady supply of water for drinking and bathing is available from troughs.

A blackbird sitting on the edge of a purple bucket with grain in its mouth.
A Brewer’s blackbird helping itself to horse grain from a bucket. Photo: Caitlin Dempsey.

Numerous nesting locations that are safe from aerial predators can be found in the stalls’ nooks and crannies. Some blackbirds get quite creative with their nest building, like this nest built on top of a rake underneath a stall overhang.

A blackbird feeding nestlings in a nest built on top of a rusty rake. A red wooden wall is in the background and a white downspout helps to support the nest.
A male Brewer’s blackbird feeds an insect to nestlings in a nest built on top of a rake hanging against the wall of a stall. Photo: Caitlin Dempsey.

Horse hair and hay provide plenty of nest material for blackbirds and other birds.

A blackbird with hay in its mouth rests on top of a horse trailer.
A Brewer’s blackbirds with hay for nest building. Photo: Caitlin Dempsey.

Blackbird males call and puff their feathers as they stand sentry on top of posts all around the upper arena.

Barn Swallows

The arrival of barn swallows (Hirundo rustica) from their wintering grounds in Central and South America marks the arrival of spring in Northern California. Barn swallows are a quintessential late winter through to summer visitor at the horse stables.

Barn swallows are small passerine birds with long, slender, pointed wings and distinctive forked tails. Passerine birds are birds who have three forward pointing toes and one back pointing toes that enables them to perch.

A black silhouette of a barn swallow in flight.
A black silhouette of a barn swallow in flight showing the forked tail. Image: Caitlin Dempsey.

Male and female barn swallows both exhibit a bluish-black upper body and wing coloration. with  orange-reddish chests and throats.

Two barn swallows sit on the metal bar of a fence.  The blurred image of a horse with its head down is in the background as well as a red wooden wall.
A mated male and female pair of barn swallows rest on the fencing of a horse stall. Photo: Caitlin Dempsey.

According to the IUCN, barn swallows are considered a species of “least concern.” While the geographic distribution of barn swallows is extensive, the number of estimated barn swallows is declining. According to North American Breeding Bird Surveys held between 1966 and 2015, the barn swallow declined 44% (Sauer et al., 2017).

A pair of barn swallows in the eaves of a barn with wood slats.
Barn swallows in the eaves of a barn in Northern California. Photo: Caitlin Dempsey.

Leapfrog migration of barn swallows

Barn swallows are migratory birds. Barn swallows in North America migrate south starting in the late summer and early fall to their wintering grounds in Central and South America. Northward migration to their breeding grounds starts as early as late January to Southern California.

The more north the breeding grounds, the later the barn swallows arrive in spring. Barn swallows tends to reach Alaskan breeding grounds around mid-May.

These barn swallows, also referred to as “leap-frog migrants,” cross over the year-round Southern California resident barn swallows to make their way to Northern California, where they will build nests and raise broods.

Barn swallows nests

These passerine birds arrive to California to breed. Barn swallows construct nests out of mud and hay in the eaves of barns and stables. Nest building is laborious, as both the male and female must make over a thousand trips to bring enough mud to create a nest.

A barn swallow sitting on a metal railing holding a feather in its mouth.
A barn swallow with a feather to be used as nesting material. Photo: Caitlin Dempsey.

Every year, barn swallows come back to reuse their nests as they can last 10-15 years. With the amount of effort needed to construct a nest, recycling old nests helps to shorten the time needed to get it ready for eggs. Nests are made from mud, hay, and feathers and are anchored up against the walls and rafters of barns and horse stalls.

An adult barn swallow perched on the outside of a nest with three nestlings inside. The nest is made of mud and hay and is against a white wooden wall.
An adult barn swallow feeds nestlings in a mud nest. Photo: Caitlin Dempsey.

The stalls also provide a protected place for fledglings once they have left the nest.

Three fledgling barn swallows on a wooden ledge with a wooden wall behind them.
The three barn swallow fledglings wait patiently on a ledge in a horse stall for their parent. Photo: Caitlin Dempsey.

Places to sing and rest

Electrical wiring gives the barn swallows plenty of places to sing from.

A barn swallow singing facing the camera on a suspended electrical wire.
A barn swallow singing from electrical wiring. Photo: Caitlin Dempsey.

Acorn Woodpeckers

The lower part of the barn is dominated by acorn woodpeckers (Melanerpes formicivorus) who take advantage of the mature oak trees to ferry acorns to granaries drilled into the utility poles and barns.

A woodpecker sits under an old street lamp on top of a wooden utility pole. The pole is full of holes drilled by the woodpecker.  Numerous trees are in the background.
An acorn woodpecker rests on top of its granary. Photo: Caitlin Dempsey.

Woodpecker granaries

Acorn woodpeckers store acorns in granaries. Numerous holes are drilled into trees and wooden buildings like utility poles and barns to create granaries.

A closeup look a acorns stored in a wooden post.
A close up look at the acorns stored in holes drilled by the woodpeckers into this wooden utility pole. Photo: Caitlin Dempsey.

Each acorn is carefully fitted snugly into each hole. As the acorn dries out and shrinks, woodpeckers will spent hours refitting the acorns into smaller holes.

Acorn woodpeckers form large extended family communities to collectively manage these granaries. A group of acorn woodpeckers is known as a bushel.

A group of woodpeckers sitting on top of a wood post that has holes with acorns fitted in to them.
A bushel of acorn woodpeckers guard their granary in a wooden utility pole. Photo: Caitlin Dempsey.

There are lots of wooden buildings in this part of the stable for the woodpeckers to set up granaries, from wooden poles to barns built in the 1930s.

A woodpecker perched on the side of a wooden barn with holes containing acorns.
An acorn woodpecker managing a granary on the side of a wooden barn. Photo: Caitlin Dempsey.


Bowman, R. H., & Estrada, D. C. (1980). Soil survey of Santa Cruz County, California. U.S. Department of Agricultural Services.×tamp=1668549309052

California ground squirrel. (2015, November 9). Ojai Valley Land Conservancy.

BirdLife International. 2019. Hirundo rusticaThe IUCN Red List of Threatened Species 2019: e.T22712252A137668645. Accessed on 06 April 2022.

Johnson, T. W. (n.d.). Out my Backdoor: Barn swallows offer unique window into nesting | Department of natural resources division. | Department Of Natural Resources Division.

Sauer, J. R.; Niven, D. K.; Hines, J. E.; Ziolkowski, Jr, D. J.; Pardieck, K. L.; Fallon, J. E.; Link, W. A. 2017. The North American Breeding Bird Survey, Results and Analysis 1966 – 2015. Version 12.23.2015. Laurel, MD


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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.