Lincoln's sparrow

There are three known subspecies of Lincoln's sparrow. However, some authors suggest that M. l. lincolnii and M. l. alticola should be considered one subspecies because of their morphological similarity.[2]

• M. l. lincolnii is generally larger with more ruddy brown or gray-brown coloring and less yellow edging on dorsal feathers.[2]
• M. l. gracilis is smaller with more yellow on dorsal feathers and broader dark shaft streaks creating greater contrasts in dorsal coloration.[2] Its breeding habitat extends from the southern Alaskan archipelago to central British Columbia.[2]
• M. l. alticola, the Montane Lincoln's sparrow, is the largest subspecies and most uniform in color with a mostly brown back and narrow shaft streaks on dorsal feathers.[2] It lives in the central Rocky Mountains of Canada and the mountains of California and Oregon and breeds as far south as New Mexico and Arizona.[2]

Lincoln's sparrow is a very secretive species; they are often not seen or heard even where they are common. Only the males are known to sing and their song is unique among the Melospiza genus.[2] They produce a sweet, wrenlike, gurgling song with varied frequencies.[3] First, there are often several rapid, high-pitched introductory notes, which then go into a trill that starts out low, rises abruptly, and then drops.[2][3] Similar to the swamp sparrow, Lincoln's sparrow has a relatively small song repertoire with an average of 3.7 different song types per individual.[7] However, their complex, multisyllabic song pattern is comparable to that of a song sparrow, whereas the swamp sparrow has a simple, single-syllabic song.[7] They sing most frequently in the morning and only in the beginning of the breeding season before incubation.[2] They often sing while exposed on perches, as well as during flight.[2]

This bird has two calls sounds: one is an aggressive, flat tup or chip while the other is a soft, high-pitched buzzy zeet.[2][3] The latter in males is often followed by their song.[2] The zeet call is generally used while under dense cover, whereas the chip call is used while exposed on perches to attract attention or during antagonistic encounters.[2] Both calls are used in nest defense.[2] They also have a distinct, hoarse, buzzing zrrr-zrrr-zrrr call sequence used for mating, during territorial disputes, and when mate-guarding.[2]

In the winter, the majority of their diet consists of small seeds of weeds and grasses, but when available they will also eat terrestrial vertebrates.[2] During the breeding season, they mainly feed on arthropods including insect larvae, ants, spiders, beetles, flies, moths, caterpillars, mayflies, and others.[2][8] Adults typically eat prey from higher trophic levels such as spiders, whereas they feed their chicks greater proportions of plant material and lower trophic level prey like grasshoppers.[9] They mostly forage on the ground in dense vegetation and, in the winter, may occasionally use bird feeders.[2] They catch prey with their bill while hopping on the ground[8] and typically swallow their prey whole.[2]

Males arrive to the breeding ground in mid to late May and begin to sing in order to attract a mate.[2] In early June, females build their nests on the ground under dense grass or shrub cover, usually inside a low willow shrub, mountain birch,[5] or sunken in a depression of sphagnum moss.[8] Their nest is a well-covered shallow open cup of grasses or sedges.[8] Clutch size is typically 3-5 eggs[2] which are oval in shape and colored pale green to greenish-white and spotted reddish brown.[8] One egg is laid per day, and females begin incubating eggs before the clutch is complete, while males do not incubate.[10] Incubation lasts for about 12–14 days.[8] Young are born altricial and leave the nest about 9–12 days after hatching, although they may be cared for by their parents for another 2–3 weeks.[8] Fledglings are mostly flightless their first day, but their flying abilities quickly improve, and by day six they can fly more than 10 meters at a time.[2]

In Lincoln's sparrows, male bill shape is correlated with the quality of their songs, with declining quality as the ratio of bill height to bill width decreases.[11] This impacts reproductive success because song quality influences female mating preferences.[11] Males that hatch later in the breeding season tend to have bill shapes that are less suitable for producing songs that attract females, and thus, have lower reproductive success.[11]