Part I: Introduction

As I walked around Sandy Island Provincial Park when I first began birding, I found myself drawn to these small sparrows with a distinct yellow stripe on their head. At the time, I didn’t know what these little guys were, or even how to identify them; all I knew was that I seemed to see them everywhere and that they were very vocal!

Description and Identification

The Savannah Sparrow (Passerculus sandwichensis) is a short-tailed grass sparrow that belongs to the Order Passeriformes and Family Passerellidae (Ebird). They are insectivores, primarily; however, during the winter months they will switch to a diet of small seeds from grasses and other flowering plants. They may seem like another boring striped songbird that looks like all the rest, but they are actually quite easy to identify! While they are not as flashy as some other bird species, they do have several distinct features.

The bright yellow lores, when they are present, an excellent field marker when searching for them. Even when the yellow is not present, they are brown above with thin black or brown streaks, and white on the belly with streaking throughout, and can range in being more greyish or reddish in appearance. (The Cornell Lab of Ornithology). They can be easily mistaken for Song Sparrows (Melospiza meodia), however they have a much shorter tail, as well as a subtle crest; their bill is considered small for a sparrow and is pinkish in colour, their streaking is a lot more distinct, and they have a paler eyebrow (Sibley, 2016).

In terms of sexual dimorphism, there is no distinct difference between males and females in plumage; however, sexual dimorphism is present between the sexes in terms of size, the juvenile males being 11% larger than the females (Wheelwright, 1994)

There are 28 named subspecies of Savannah Sparrow (Bird Atlas), some of which experience distinct plumage and other differences by region. Subspecies includes the “Large-billed”, “Belding’s”, and “Ipswich” Savannah Sparrow (The Cornell Lab of Ornithology). As one of my professors would say, Holy Biodiversity Batman!

Fun fact! The Ipswich Savannah Sparrow nests only on Sable Island, Nova Scotia! They are larger and paler than their eastern counterparts of Savannah, and prefer to walk or run, rather than hopping as the other races tend to do (Robbins, 1983).

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Their song is a series of fine high pithed buzzes that get lower in pitch and longer in length, ending in a tsss call. Have a listen!

Distribution

Savannah Sparrows are medium range migratory birds, having some resident populations along the coast of California and parts of Mexico. They depart for their wintering grounds sometime between mid-September and early November. During the spring migration, they arrive at the breeding grounds from late February in the more southern areas, to early May in the more northern areas. Males tend to arrive earlier than females to claim territory (The Cornell Lab of Ornithology).

Habitat and Nesting Locations

Savannah Sparrows are considered to be habitat generalists throughout the majority of its range (Peterson, 2014) , but will typically nest on the ground in the shelter of tall grass or shrubs. These habitats can be either natural or man-made, including grasslands and shrubbery, weedy field-edges, pastures and hayfields, marshes and estuaries, alpine meadows and arctic tundra (Bird Atlas).

They make their nests amongst the thick shrubbery of the previous years foliage in densely vegetated areas. The female makes a nest that is approximately three inches in diameter, and one inch deep. This allows the female the perfect size to lay a clutch of 2-6 eggs, which she will nest and incubate for around two weeks. Females have the tendency to choose a spot at the edge of her mate’s territory, often forcing him to compete with neighboring males (The Cornell Lab of Ornithology). Rude.

Conservation

Even though at the current moment Savannah Sparrows are of low concern, populations are on the decline across Canada (Bird Atlas). A study done in Churchill Manitoba showed that the increased population of Lesser Snow Geese has led to severe habitat degradation, resulting in a trophic cascade that has had a negative impact on plant, insects, and other avian species that occupy the area. What has caused this cascade is the destruction of the habitat due to “grubbing”. This is where Lesser Snow Geese dig shallowly under the earth when searching for food. This process exposes the upper layer of soil, allowing salt to seep upward and increasing the soil salinity, leading to increased mortality of dwarf shrubs; one of the main preferred shrubs of Savannah Sparrows (Peterson, 2014).

In the past few decades, the Savannah Sparrow population has decreased by 80% in that area alone. That’s crazy!

Part II – Love you Like a Love Song

Birds sing for a multitude of reasons, but it all comes down to one major thing: communication! Like serenading your significant other on a date, bird song plays an important role in finding a mate in avian social structure (Catchpole, 2008). Using this fact, several studies have been done on the relationship comparing song and territory quality of males to the success of mate selection and reproductive success in Savannah Sparrows.

From what you remember from the description of Savannah Sparrows, as well as from seeing the photos, you now know that they are not sexually dimorphic. This means that the male isn’t using his plumage to catch the attention of his potential mate, so instead he will compete by other means; in this case by song.

Due to this prevalence of song being used as an indicator of fitness, there are going to be selective pressures on the song performed by the males. An experiment done on a population of Savannah Sparrows on Kent Island, New Brunswick, Canada over the course of three decades showed that the songs and the quality of the territory of the males possessed were related. Males that had a lower thrill had lower reproductive success, and males that had higher click trains had higher reproductive success (Williams, 2013).

Another study, also performed on Kent Island, showed that males who arrived to the breeding grounds earlier had better territory were mated quicker, and had larger fledging success than males who arrived later were not as successful and experienced sexual selection on their song (Sung, 2020).

Conclusion

Due the constant sexual selection the song of male Savannah Sparrows experience, their song will experience a cultural evolution that will result in the changes of certain parts of the song, perhaps evolving an entirely different song altogether! However, we need to keep a special eye on these beauties, as their population continues to decline. It is entirely possible that Savannah Sparrows can evolve to become territory specialists, resulting in further sexual selection on their song… possibly leading to entirely new species over time.

References

Atlas of The Breeding Birds of British Columbia. Savannah Sparrow. (Internet): https://www.birdatlas.bc.ca/accounts/speciesaccount.jsp?sp=SAVS&lang=en

Catchpole, C.K., and Slater, P.J.B. Bird song: biological themes and variations, 2nd ed, Cambridge University Press, Cambridge, 2008.

Peterson, Stephen L., et al. “Legacy Effects of Habitat Degradation by Lesser Snow Geese on Nesting Savannah Sparrows.” The Condor, vol. 116, no. 4, 2014, pp. 527–537.

Robbins, Chandler S., et al. A Guide To Field Identification – Birds of North America Expanded, Revised Edition. New York, Golden Press, 1983.

Sibley, David. Sibley Birds West – Field Guide to Birds of Western North America, Second Edition. New York, Alfred A. Knopf, 2016.

Sung, Ha-Cheol, and Paul Handford. “Song Characters as Reliable Indicators of Male Reproductive Quality in the Savannah Sparrow (Passerculus Sandwichensis).” Canadian Journal of Zoology, vol. 98, no. 1, 2020, pp. 32-38.

The Cornell Lab of Ornithology (2019) All About Birds: Savannah Sparrow. (Internet): https://www.allaboutbirds.org/guide/Savannah_Sparrow/overview

Ward, Peter. Ken, Hall. “Savannah Sparrow – Adult Male Song” Xeno – Canto: Sharing bird sounds from around the world. (Internet): https://www.xeno-canto.org/explore?query=Savannah+Sparrow&dir=0&order=cnt

Wheelwright, Nathaniel T., et al. “Sexual Dimorphism and Population Sex Ratios in Juvenile Savannah Sparrows (Dimorfismo Sexual y Razón De Sexos En Juveniles De Passerculus Sandwichensis).” Journal of Field Ornithology, vol. 65, no. 4, 1994, pp. 520–529.

Williams, Heather, et al. “Three Decades of Cultural Evolution in Savannah Sparrow Songs.” Animal Behaviour, vol. 85, no. 1, 2013, pp. 213-223.