Let this little bird creep its way into your heart.

Part one: Introducing the Brown Creeper.

The Brown Creeper (Certhia americana), also known as the American treecreeper, is a small songbird found primarily in large forests throughout Canada and the United States (The Cornell Lab of Ornithology, 2017). The Brown Creeper is from the order Passeriformes and the family Certhiidae. Adult Brown Creepers have an average body length of 5.25 inches, a wingspan of 7.75 inches, and a body weight of 8.4 grams (Sibley, 320).

The ideal habitat for a Brown Creeper is a damp, shady forest with large, loose-barked trees for catching prey and nesting. These birds like to nest in the biggest trees that they can find. Dead or dying trees are the most appealing to a Brown Creeper because they like to build hammock-like nests under the detaching bark. In the summer months they tend to live in coniferous forests, while in the winter months they expand their habitat preference to deciduous forests, orchards, and parks. Brown Creepers are dispersed all over the United States as well as in all the Canadian provinces along the US border. They have been reported to be seen in Central America year round, but they are most abundant in North America. In the winter months, Brown Creepers that live in high altitudes and Northern populations will migrate South for a short distance (The Cornell Lab of Ornithology, 2017).

Did you know that Brown Creepers are the only treecreepers that are found in North America?

The nests are built by male and female creepers; The females assemble the nest over the course of a few weeks while the male goes out and gets nesting material. Some of the materials used are mosses and lichens, feathers and hair, wood pieces, leaves and grass, and spider egg cases. Nests are built at many different heights, but they do not usually exceed 40 feet in the air. The Brown Creeper nest is around 2.5 inches deep and 6 inches wide which is good for holding eggs. The size of a Brown Creeper egg is 1.5 cm by 1.2 cm (length by width). The breeding season of these little birds is normally between April and July. Female creepers can lay up to 6 eggs which have an incubation period of 13-17 days. Once hatched, the babies stay in the nest for 14-20 days before they will start to go off on their own.

A risk to the nests of brown creepers are different types of squirrels and mice that may destroy the nest if they come across it (The Cornell Lab of Ornithology, 2017). Some common predators to the Brown Creeper are squirrels, deer mice, wood rats, and domestic cats (Animal Diversity Web).

Brown Creepers are insectivores who find their food by flying to the base of a tree and start creeping up by using their long curved claws to hold onto the bark. While climbing, they use their downward curved beak to reach into the bark to eat many different insects including beetles, spiders, and ants. When a predator is near, Brown Creepers immediately stop moving and making any sounds as they press their undersides to the bark and rely on their camouflage to avoid being detected (The Cornell Lab of Ornithology, 2017).

Did you know that by eating one single spider, a Brown Creeper gets enough energy to climb approximately 200 feet vertically?

Brown Creepers are small brown birds with primarily white undersides. Some good characteristics to help identify a Brown Creeper are the long claws on the toes, the downward turned bill, and the mottled brown back that helps the creepers to blend into the bark of the tree they are creeping on. Brown Creepers also have a light, bold band on the tops and bottoms of their wings, as well as a light lateral crown stripe above their eyes. There are three different color variations for the Brown Creepers; the first being the classic light brown, mottled back we see in the Northern and Eastern plumage. In the Western plumage they have a more grey back, but they still have the white throat and underside. The third color variation is the Mexican plumage which is seen more in the Creepers down in Central America. The Mexican variation is a lot darker with a reddish-brown rump and a grey breast rather than the white breast we see in the other two variations (Sibley, 320). Male and female Brown Creepers look very similar, but one characteristic that can be helpful to determine the sex of these birds is to look at the length of the curved bill. The males tend to have a longer bill by around 1-2 mm (Animal Diversity Web). Here on Vancouver Island, we primarily see the Northern plumage.

The behavior that is most commonly observed in the Brown Creeper is the climbing of the tree. They climb up the tree from bottom to top, rarely going down, by hopping and latching onto the bark with their claws. Once they get to the top of the tree they will fly down to the base of a new tree and start climbing again. While climbing the trees, the bird used its stiff tail to brace itself. Brown creepers are thought to be monogamous and parents stay together until after their offspring have left the nest.

A fun fact about Brown Creepers is that only the males sing.

The males sing during the breeding seasons to defend their territories of 5-15 acres and to assert their dominance amongst other males. They also sing when looking to mate with local females in their area, as well as to protect their nest sites (The Cornell Lab of Ornithology, 2017). The song of the Brown Creeper is a series of high pitched noises that ends on a very high note. It resembles “seee sitsweeda sowit-see” or “trees trees pretty little trees” (Sibley, 320).

The conservation status of brown creepers was stable between 1966 and 2015. They are still not on a watch list for being at risk, but deforestation poses some issues to the Brown Creeper. Many dead or dying trees in the west are being cut down for timber sales which gets rid of many potential nesting sites. Forests are also becoming more fragmented which also can lead to problems for the Brown Creeper because they rely on forests and trees as their hunting grounds. New England is starting to become a hot spot for Brown Creepers because many of the trees in their forests are dying. Dutch Elm disease and gypsy moths are killing these trees which as a result creates good nesting sites for Brown Creepers ( The Cornell Lab of Ornithology, 2017 ).

Part two: Breeding behaviors of the Brown Creeper in El Salvador.

Breeding behaviors for Brown Creepers in El Salvador are quite interesting. Brown Creepers are insectivores, and most insectivores time their breeding to match the hatching of their young with the rainy season. This means that insectivorous birds normally hatch around May or June. They do this because the number of insects available to eat increases greatly during the rainy season. In El Salvador, the dry season runs from November until April, therefore the rainy season runs from May until October (Bolaños, Funes, Komar. 2012).

Brown Creepers were recorded on February 5, 2010, in Chalatenango Department, El Salvador. They were recorded between the hours of 11:30 AM – 12:30 PM and 3:20 PM – 4:25 PM. The nest that was recorded was at a height of 1,470 meters above ground with fledglings that were approximately one week old. Since Brown Creepers have an incubation period of around 15 days, it was thought that incubation began around January 12, 2010. This is interesting because they hatched during the dry season which is out of the normal for insectivorous birds. The adults would leave the nest to find food for the newborns and would return every 2 – 30 minutes (Bolaños, Funes, Komar. 2012).

There is not any evidence of any other birds that breed regularly during the dry season in El Salvador. A Brown Creeper that was caught on April 10, 2008, in Montecristo National Park in El Salvador, was classified as being in its second year. It was molting contour feathers and still had worn juvenile flight feathers. By looking at the feathers of this bird they were able to narrow down its hatch time to be during February of 2007. That would mean this Brown Creeper was also hatched during the dry season (Bolaños, Funes, Komar. 2012).

Nesting early in Central America may mean that the local subspecies of Brown Creeper is on its own evolutionary track that differs from the Northern subspecies we see here. This could potentially lead to the evolution of phenological barriers to gene flow (Bolaños, Funes, Komar. 2012).

References

The Cornell Lab of Ornithology. 2017. All About Birds: Brown Creeper. [Internet] https://www.allaboutbirds.org/guide/Brown_Creeper

Sibley, D.A. 2016. Sibley Birds West: Field Guide to Birds of Western North America. Second Edition. Alfred A. Knopf, New York, New York. P. 320.

Damon Calderwood. Fineartamerica. Brown Creeper at Nest. June 8th, 2016. [Internet]
https://fineartamerica.com/featured/5-brown-creeper-at-nest-damon-calderwood.html

Birds of North America. Brown Creeper. [Internet] https://birdsna.org/Species-Account/bna/species/brncre/introduction

Bolaños, O., Funes, C., Komar, O. 2012. Breeding of the Brown Creeper (Certhia americana) in Central America. Wilson Ornithological Society. 177-179.

Tough little birds. Little creeper and creeping bycatch. July 18, 2013. [Internet] https://toughlittlebirds.com/tag/fledglings/

Animal Diversity Web. Certhia americana. [Internet]
https://animaldiversity.org/accounts/Certhia_americana/#predation