Introduction

Data Collection

Observations and Analysis

Summary
Songbirds: All Year Residents
Songbirds: Summer Residents
Songbirds: Winter Residents
Other Bird Species

Concluding Remarks

Appendix A: Dawn, Twilight and Light Intensity

Appendix B: Dawn Participants

Acknowledgment

References

Introduction

In my Home 'patch' in the Northeastern USA, pre-sunrise vocalization of birds or dawn chorus begins around the vernal equinox. With warmer temperatures and the approaching breeding season, resident birds begin to sing half-hour to an hour before sunrise. From mid-April to mid-May, summer migrants join the chorus. The dawn chorus begins to fade in late August and ends by the beginning of September.

Dawn chorus has been studied for hundreds of years [1] and reviewed recently [2, 3]. The motivations for dawn singing may be divided into three different classes. The first set is related to the breeding cycle; hormone levels, mate attraction, communications with mates and nestlings, and territorial defense. The second set is safety and food availability; low light levels for minimizing predator attacks, fixed perches to avoid detecting movements, sharing of food source information, social interactions within species and across species. The third set is environment related; low noise and better sound transmission, sky conditions, temperature, and humidity levels favorable for vocalization.

Songbirds or passerines of the order Passeriformes are the main participants in the dawn chorus. Each species may have many different vocalization patterns. Typically, songs comprise phrases composed of one or more syllables and often repeated at regular time intervals. Calls are short, simple notes used for communications such as predator alarms, 'I am present', and 'Here is food'. Singing in most songbird species is attributed to males although some females may also sing specially during breeding season. Many other species also vocalize before sunrise - a flock of Canada Geese in flight honk, Barred Owls hoot and Mourning Doves coo.

The clock time at which each species initiates vocalization has been correlated with light intensity and their eye size. In a study conducted in United Kingdom, Portugal and Switzerland, birds with larger eye size and body mass are reported to initiate singing earlier [4]. Other reports also conclude that ambient light levels affect the singing behavior of songbirds [5, 6].

We examined these hypotheses on the observations made in the Home 'patch'. Dawn singing was clearly related to the nesting period. We understand that the composition of a dawn chorus may vary largely with habitat variations even within the same geographical area. This makes it difficult to generalize bird behavior based on a limited number of individuals. However, the fact that some individuals were observed to begin singing at a fixed time before sunrise, irrespective of the light intensity level, indicates the presence of an internal mechanism tuned to the sun in these birds, contrary to some scientific reports.

Data Collection

My house, which is on a dead-end street with no streetlights, served as a blind. I listened through three different windows pointing towards 1) southeast, 2) southwest and 3) northwest. These cover areas of the Home 'patch' in front of the house and the woods behind the house which extend to a nature reserve. There were no bird feeders on this street and the surroundings provided a natural environment. The traffic on the street at this early hour was negligible. As I, the observer, was inside the house, the birds were not perturbed by my movements.

I listened attentively and simultaneously made audio recordings using the Merlin App from Cornell University installed on an iPhone. A small shotgun microphone was attached to the iPhone for reducing background noise. To capture far away sounds coming from different directions the microphone was rotated to cover an angle of about +/- 30^o. The species were identified by listening by ear and confirmed by matching the spectrogram generated in Merlin. Single instances of bird calls, identified by Merlin, when overlapping with several other species calls and not distinctly heard were not included.

Listening to and recording bird species vocalization in a three-minute period were done. The process was repeated once every 15 minutes, from 75 minutes before sunrise to just after sunrise. These quarter-hour time windows are designated Q1, Q2, Q3, Q4, and Q5 The two quarter-hour time windows after sunrise are labeled P1 and P2. These time window assignments are shown below:

 

StartTime is defined as the clock time at which a bird species begins to vocalize. Data collection began on March 24^th, 2023, and ended on September 9^th, 2023. From April 15^th, once the daily pattern of dawn chorus was established, I listened for at least 15 minutes before the first bird species was expected to initiate singing and carefully noted the StartTime of the first few species. Listening then continued in approximately 3-minute periods in the middle of each Quarter. Light intensity was measured in each quarter using a light meter (Dr.meter model LX1330B.) The local twilight timings and the light intensity measurement results are described in Appendix A.

Data were entered in the 'AvianActs Vocalization' (AAV) database (under development.) This information was linked with the AvianActs Phenology (AAP) database which includes arrival dates of migratory species, nesting records, favored food sources for each species, and local weather. We used this data to study the behavior of species that reside and breed in the vicinity of the Home 'patch'. The order in which species begin to vocalize, duration of vocalization and how these patterns changed as the seasons progressed were analyzed.

Observations and Analysis

Summary

Table 1 lists the number of observation days, the species count for songbirds, classified in the order Passeriformes, and other bird species. Out of the 37 songbirds, 19 species are present all year in this area of Northeastern USA, 15 migrate from the south in the summer for breeding, and three species migrate from the north to spend the winter here. Using the guidelines provided by New York State Breeding Bird Atlas, 20 species were confirmed as nesting in the 'Patch'. The nests of American Robins, Northern Cardinals, Chipping Sparrows, and Carolina Wrens were located next to the house, and their nesting activities were observed regularly.

Table 1. Dawn chorus participation summary

 

There was some variation in the number of species vocalizing in dawn from day-to-day. Hence, we counted the total number of unique species vocalizing in each Quarter in a week. Fig. 1 shows the unique species each week for Quarters Q1 through Q5. The total count of unique species vocalizing before sunrise shown in Fig. 2 varied from 6 to 25. Note the following:
Weeks 12, 13: The count was low in the beginning of the season.
Week 15 (third week in April): The weather was unseasonably warm, and birds were more active.
Weeks 29, 30: I was away part of these weeks; hence the count may be low due to fewer observation days.
Weeks 33 through 36: The birds stopped vocalizing in Q4 by week 32, in Q3 by week 34 and overall participation in the dawn chorus dropped by week 36.

 

Fig. 1 Number of bird species heard vocalizing in each Quarter before sunrise by week.

 

Fig. 2 Species count participating in dawn chorus by week.

 

In Fig. 3, the average StartTime of all songbirds is plotted vs. average body mass. The data are fitted to a linear trendline. The R² value is 0 and there appears to be no correlation or evidence of birds with larger mass and therefore larger eye-size singing earlier than others. We also found that the StartTime of several species was independent of the light intensity level. These findings are contrary to other reports [4, 5, 6] and the general belief that birds begin to sing as the light level increases with the approach of sunrise. If this were the case, these birds' StartTimes would also depend on sky conditions.

Fig. 3 Average StartTimes of songbirds vs. body mass.

We focused our study on individual species with confirmed breeding codes, tracking their StartTimes and the duration of singing with sunrise and twilight timings. These are described in the following sections using standardized plots of StartTimes and number of participation Quarters covering the observation period from March 24^th to September 9^th, 2023. We observed that in most cases, dawn chorus participation was more regular during the nesting period of a species and either ended or much reduced afterwards.

StartTimes were also accurately tracked with light intensity levels at dawn for American Robins and Chipping Sparrows. The internal clock of these two species studied here appeared to be well-tuned to the time of sunrise and independent of light intensity. The StartTimes for several other species, though recorded with larger uncertainty (+/- 6 min) also tracked with the time of sunrise.

Songbirds: All Year Residents

The term 'all year residents' is applied here to the species found year-round in this part of Northeastern USA. The individuals of species such as Tufted Titmouse and Black-capped Chickadees may remain in the same locations. Others such as American Robins and Red-winged Blackbirds may migrate within their distribution range.

There were 19 all year resident songbird species heard in the dawn chorus at least once. Table 2 lists the breeding codes for 11 of these species confirmed nesting in the vicinity. Two different nests of Northern Cardinals, and two of American Robins, and one of Carolina Wrens were located close to my house. Four additional species, Black-capped Chickadees, Eastern Bluebirds, Red-winged Blackbirds, and American Goldfinches, were probably nesting in the vicinity. Either adult pairs were seen together and/or young birds were seen later in the season. American Crows and Fish Crows were heard in flight and Common Grackles called a few times at dawn. Brown-headed Cowbirds are parasite brooders and were around in search of host nests.

Table 2 Breeding codes for all year residents participating in dawn chorus.

 

1.      American Robin

A few American Robins were occasionally spotted during the winter of 2022-2023. Small flocks of about ten birds were first seen on March 15^th. Larger flocks of 20 or more were seen between March 24^th and April 2^nd. Four to six robins were around and singing at dawn all spring and summer. On most days, this was the first species to be heard in the morning chorus. The birds continued to sing after sunrise and sporadically all day, ending the day with continuous singing at dusk.

Fig. 4 StartTimes of American Robin, sunrise, civil and nautical twilights from March 24^th to September 9^th, 2023. Black crosses (x) on the sunrise line indicate days on which no observations were made.

Singing began softly, and it took a minute or so to get the full volume and cadence of the 'charlie, cheerie, cheery-up' song. Fig. 4 shows the StartTimes for American Robins along with the time of sunrise and onset of civil and nautical twilights. The StartTime was around the beginning of civil twilight in early spring. As the season progressed, robins began to sing earlier. By mid-spring through early summer (May, June, and early July), the StartTime was about an hour in advance of sunrise which is before the beginning of civil twilight. By late July, the StartTime moved back to the commencement of civil twilight. Starting in the first week of August, robins were vocalizing with calls but not singing the 'charlie, cheerie, cheery-up' song. These calls are indicated by red triangles in Fig. 4.

Figure 5 shows the number of Quarters in which robins were singing before sunrise. By mid-April, the StartTime was earlier than the commencement of civil twilight and singing persisted through the four to five Quarters before sunrise and continued after daybreak.

Was the singing triggered by the change in light level? In Fig. 6, the StartTime with respect to sunrise is plotted vs. measured light intensities measured at about 8 minutes before sunrise (middle of Q1) and about 23 minutes before sunrise (middle of Q2) from May 23^rd to June 26^th. In this 34-day interval, the time of sunrise varied by only six minutes. StartTime for robins singing remained fairly constant within the errors in measurements (average = 52 minutes before sunrise, standard deviation = 3 min, total variation = 11 minutes) even though the light intensity varied by a factor of 16. Rain, clouds, or clear skies had no measurable impact on the StartTime. See Light Intensity Measurements in Appendix B for more details. >

Fig. 5 Number of Quarters (Q1 through Q5) in which American Robins were singing at dawn.

Fig. 6 StartTimes of American Robin from sunrise vs. light intensity in Quarters Q1 and Q2. Time for sunrise, shown as orange line, is designated as zero.

There were at least two pairs of robins nesting close to the house and another two or three pairs within the HomeYard 'Patch'. One female robin was first seen collecting nesting material and building a nest in a shrub on April 16^th. Another nest on a Lonicera Sempervirens vine next to my house wall was first observed on June 13^th and contained four eggs. The last nest was somewhere nearby, and robins were carrying food to the nest. All activities related to bringing food to the nestlings appeared to have ended by August 2^nd. These observations are consistent with three broods in the season, typical for robins in this region.

Based on this data, we make the following observations:

1.      Robins were generally the first birds to start singing at dawn during the nesting season.

2.      The StartTime was related to the time of sunrise and not the light intensity level. The birds appeared to have an internal clock synchronized with the sunrise.

3.      Robin StartTime was earlier during the nesting season - 50 to 55 minutes before sunrise - than before the start of the nesting season.

4.      Singing was much reduced by the beginning of August, and vocalization changed from song to call.

2.      Northern Cardinal

A male Northern Cardinal began singing during the day around February 20^th. His whistled songs were heard at dawn all through the breeding season and dominated the chorus when he was nearby. The StartTime was less regular than that of robins but consistently in Q4 for May and June. During this period he was heard in three or four Quarters before sunrise.

Nest-building began on April 12^th, and the first brood fledged on May 13^th. By the second week of August, while the robins stopped singing at dawn, the cardinal continued. A second nest was located on August 5^th, and the female was seen sitting on it on August 12^th. The chicks fledged on September 1^st. Immediately after that the cardinal stopped singing and switched to chip calls, shown as orange triangles in Fig. 7. His extended presence in the dawn chorus appears to be related to the extended breeding season.

Fig. 7 StartTimes of Northern Cardinal, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

3.      Carolina Wren

Here Carolina Wrens sing all year, even in the middle of winter. Their participation in the dawn chorus was noted from the start of this project on March 24^th and continued until the end. The StartTime was more consistent except in June. Recently fledged young were seen on June 24^th with adults bringing food. Nest construction under the lid of a propane tank next to the house started in the next few days. Nest with five eggs (four wren's eggs and a Brown-headed Cowbird egg) was observed on June 30^th. All eggs hatched successfully by July 14^th.

These wrens are reported to have two broods in a season, rarely three in the Northeast. From the dawn singing, it appears that the nest in early June was some distance away and the StartTime varied whereas the StartTime was more consistent in July when the nest was close to the house.

Fig. 8 StartTimes of Carolina Wren, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

4.      Northern Mockingbird

A pair of Northern Mockingbirds was nesting nearby, and fledglings were spotted with the parents on June 18^th. Mockingbird rarely participated in dawn chorus and because of the ambiguity created by his rich repertoire mixed with other bird songs, we chose not to include him in our analysis.

5.      Song Sparrow

A Song Sparrow participated regularly in the dawn chorus from mid-April to early-May and only for a few days in June. The StartTime was close to the onset of civil twilight. One bird was collecting nesting material on May 21. The birds were not seen or heard in the Home 'patch' after the end of June.

Fig. 9 StartTimes of Song Sparrow, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

6.      Eastern Bluebird

Eastern Bluebirds nest somewhere in the woods behind the house. Dawn chorus participation was observed only in June and early July. StartTime was close to the onset of civil twilight. Several recently fledged young were first seen on July 11^th while parents were still bringing food to them. Their participation in the dawn chorus coincides with the nesting time in June and early July.

Fig. 10 StartTimes of Eastern Bluebird, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

7.       House Finch

A male House Finch, perched on top of a nearby tree, sang every morning at dawn from early April to late July. The StartTime was consistently close to sunrise.

House finches nested on the gutter next to my front door in 2020, 2021 and 2022. In 2023, they were nesting nearby - perhaps somewhere around a neighbor's house. The first sighting of fledglings was on June 5, 2023 - two or three young ones were following the parents.

Fig. 11 StartTimes of House Finch, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

8.      Tufted Titmouse

Titmice were heard singing during the day starting in mid-February and joined the dawn chorus from March 24^th onwards. StartTime was in the civil twilight period or immediately after sunrise. Because of the late StartTime, Titmice were heard only in one or two Quarters.

The location of nests and the breeding season (one or two broods) in the Home 'patch' is not known. Fledglings were first seen on June 15^th. A small group of four to six Titmice were seen and heard regularly until early September.

Fig. 12 StartTimes of Tufted Titmouse, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

9.      White-breasted Nuthatch

The StartTime of White-breasted Nuthatches was close to sunrise. Regular participation began in mid-June. On June 5^th, adults were seen bringing food to several fledglings. Dawn singing then continued until September. nuthatches have only one brood per season. It appears that they were nesting elsewhere and regularly participated in the dawn chorus in my Home 'patch' only after their nesting season was over.

Fig. 13 StartTimes of White-breasted Nuthatch, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

10.      European Starling

European Starlings have many calls and may imitate other bird calls. There is only one instance of confirmed participation in the dawn chorus on May 28^th. The birds were nesting in the vicinity and fledglings were spotted following the adults during the week of May 22^nd.

11.      Blue Jay

The calls of Blue Jays were heard at dawn in April and early May. No participation was noted in late May and early June. After the middle of June, several Blue Jays were heard regularly during the civil twilight period.

Fig. 14 StartTimes of Blue Jay, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

12.      Black-capped Chickadee

Black-capped Chickadees were frequently singing at dawn. Participation was less regular after the end of June.

Fig. 15 StartTimes of Black-capped Chickadee, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

13.      Red-winged Blackbird

A male Red-winged Blackbird was vocal until the end of May and sporadically at sunrise thereafter. Young Red-winged Blackbirds were seen foraging on the grass in the third week of June.

Fig. 16 StartTimes of Red-winged Blackbird, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

14.      American Goldfinch

American Goldfinches were heard regularly from July 28^th to September 3^rd. This species nests late in the season and participation in the dawn chorus is consistent with the breeding time.

Fig. 17 StartTimes of American Goldfinch, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

Songbirds: Summer Residents

We classify summer residents as those that arrive from the south in spring and breed here. Migration continues from late March through mid-May. Species that stop briefly in this area during migration and breed further north are not included in this study.

There were 15 summer resident species that participated in the dawn chorus. We found confirmed breeding codes for seven of these species listed in Table 3. In addition, Eastern Phoebe was probably nesting in the vicinity as one or more birds were seen regularly. Barn Swallows and Tree Swallows were among the early risers, but their high-pitched notes in flight were often faint and difficult to validate. Eastern Kingbird, another species with high pitched songs, was detected well only in mid-July and young adults were spotted on August 24^th. Other species heard only on a few occasions and are not included.

 

Table 3 Breeding codes for summer residents participating in the dawn chorus.

 

1.      Chipping Sparrow

Chipping Sparrow arrived on April 1^st and was first heard in the dawn chorus on April 5^th. From the differences in the sound volumes, it was easy to detect that there were at least two birds singing. Once started, these birds continued singing all through dawn - typically heard in three or four Quarters in May through July.

The StartTime was about 20 minutes before sunrise in April and increased to 40 to 50 minutes in May and June. Singing began soon after the robins and it may be that their singing was triggered by that of robins. If that is so, no other bird species followed the robins so consistently. By late July, StartTime reduced to about 30 minutes before sunrise. These birds stopped participating in the dawn chorus after August 5^th. and at the same time stopped vocalizing during the day also. Two adults and one juvenile were regularly seen after August 5^th, silently feeding on the ground, and a mixed flock of 20 adults and juveniles was seen in September.

Two pairs of Chipping Sparrows built their nests in the Home 'patch', one in the backyard and one in the front yard. Nest-building began in a Hydrangea vine under the deck on May 1^st. Three Chipping Sparrow eggs and two Brown-headed Cowbird eggs were found in this nest on May 9^th. A second nest was found in the Pencil Holly in the front yard on May 31^st. It had one sparrow egg, one just hatched chick and one cowbird egg. Chipping Sparrows were last seen carrying food on July 7^th. The breeding season was from May 1^st to mid-July, with possibly two broods.

Their StartTimes appeared to be independent of the light level but varied more than for robins. The average StartTime in Fig. 19 is 45 minutes before sunrise and the standard deviation is 6 minutes. Note that a Chipping Sparrow weighs only 12 g and is one of the smallest bird species in the chorus. It is 1/6^th the mass of American Robin, yet both species began singing at about the same time.

Fig. 18 StartTimes of Chipping Sparrow, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

Fig. 19 StartTimes of Chipping Sparrow from sunrise vs. light intensity in Quarters Q1 and Q2. Time for sunrise, shown as orange line, is designated as zero.

2.      Baltimore Oriole

A pair of Baltimore Orioles were first seen in the Home 'patch' on May 8. The male was singing away during the day, and the female was collecting nesting material. The participation in dawn chorus was minimal. The male sang only a few times just around sunrise but was vocal many times during the day.

On June 22^nd and June 24^th, one or more fledglings were followed by the parent bringing food.

Fig. 20 StartTimes of Baltimore Oriole, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

3.       Red-eyed Vireo and

4.       Yellow Warbler

A Red-eyed Vireo and a female Yellow Warbler were seen hunting insects in the woods behind my house and then flying away carrying the catch. There is only one instance of each of these species' participation in the dawn chorus. Their nests may have been located further away.

5.       Eastern Wood-pewee

Eastern Wood-pewee announced his arrival by the melodious 'PEEaweee' song on May 15^th. He stayed in the woods and was only occassionally seen, but his voice reverberated in the woods. His continuous participation in the dawn chorus began in late July just as other bird species were becoming silent, and continued through the beginning of September. Fledglings, exhibiting larger gapes in the bill, were first seen on July 30^th.

From the dawn chorus participation, it appears that the Wood-pewees may have started a second nest close by after their first brood fledged.

Fig. 21 StartTimes of Eastern Wood-pewee, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

6.       House Wren

One House Wren was first spotted on April 27^th and heard in the dawn chorus on May 2^nd. Participation in the chorus continued until the end of August, typically in the civil twilight period. Four or more fledglings were spotted on June 19^th.

Fig. 22 StartTimes of House Wren, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

7.       Gray Catbird

Gray Catbirds arrived in the Home 'patch' on May 7^th. A pair may have been nesting in nearby shrubs but the nest was well concealed. A catbird was seen carrying nesting material on May 17^th. Catbird's StartTimes in the dawn chorus varied, typically in the civil twilight period or just after sunrise.

Fig. 23 StartTimes of Gray Catbird, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

8.       Eastern Phoebe

An Eastern Phoebe was first spotted on March 30^th and first heard in dawn chorus on April 12^th. He participated regularly until the middle of May and then heard on many days with gaps in between.

Fig. 24 StartTimes of Eastern Phoebe, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

Songbirds: Winter Residents

Dark-eyed Juncos and White-throated Sparrows are seen in my Home 'patch' all winter. juncos were singing before sunrise from the time I started recording on March 24^th and continued until April 14^th. These birds were last seen on April 16^th before migrating north for the summer.

White-throated Sparrows were first heard singing at dawn on April 12^th and continued until last seen on May 15^th. During this time, they were also singing after sunrise and occasionally during the day.

These two bird species do not breed in this area. Hence, their singing is not related to protecting breeding grounds.

Ruby-crowned Kinglet, another winter resident, was heard only once on May 16^th.

Fig. 25 StartTimes of Dark-eyed Junco and White-throated Sparrow, sunrise, civil and nautical twilights from March 24^th and September 9^th.

Other Bird Species

StartTimes and participations of several other species are shown below. These include Mourning Doves, Red-bellied Woodpecker, Canada Goose and Barred Owl, each belonging to a different order than songbirds.

1.       Mourning Dove

Mourning Doves were regular participants, but the StartTimes with respect to sunrise were variable.

Fig. 26 StartTimes of Mourning Dove, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

2.       Red-bellied Woodpecker

Red-bellied Woodpeckers called around sunrise fairly regularly between May 7^th and May 23^rd. These birds do breed in the vicinity. A juvenile with a bald head was spotted on August 9^th.

Fig. 27 StartTimes of Red-bellied Woodpecker, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

3.       Canada Goose

Canada Geese honk in flight as they pass this area before sunrise. One pair nested near the pond across the street from my house and goslings were present in the first week of May. The flights were discontinued in June and July when the geese are molting.

Fig. 28 StartTimes of Canada Goose, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

4.       Barred Owl

Barred Owls typically call at night. In the months of April and May, one owl was hooting at dawn.

Fig. 29 StartTimes of Barred Owl, sunrise, civil and nautical twilights; and number of participation Quarters, from March 24^th and September 9^th.

Concluding Remarks

In March of 2023, I started listening to birdsongs at dawn to learn more about birds in the neighborhood and to hone my skills in bird identification by songs. By the end of the first week, I realized that different bird species vocalized at different times. Our team member Hemant Sogani who resides in India and I devised a scheme for recording and analyzing the data and created a database to track the StartTimes more accurately. As the season progressed, the birds were starting to sing earlier and earlier and my desire to know how well their StartTimes tracked with sunrise made me keep up with them.

It was enlightening to learn how some birds coordinated their singing with nesting, and ending abruptly when the last brood of the season fledged. Conversely, one may know of the nesting period of a species by their singing regularity at dawn.

There is a saying that "Cocks crow in the morn to tell us to rise, and he who lies late will never be wise." Fortunately cocks crow just at sunrise when there is sufficient light, and it is not much of a hardship to wake up then. In this area some songbirds appear to be much wiser, knowing the time of sunrise an hour ahead even when there is cloud cover or rain. I, on the other hand, depended on an alarm clock to wake me up.

I am aware that if there is no pressure to do otherwise, I am always wide awake just around sunrise - earlier in summer than in winter. Keeping up with American Robins and Chipping Sparrows for me was an arduous task. Perhaps I should limit my study to House Finches next year or switch to listening to dusk chorus.

Appendix A: Dawn, Twilight, and Light Intensity

Dawn and Twilight

Civil, nautical, and astronomical twilights are defined with the sun at 6^o, 12^o and 18^o below the horizon respectively as illustrated in Fig. A1.

 

Fig. A1 Position of the sun at sunrise, and at the onset of civil, nautical, and astronomical twilights.

Sunrise: Sunrise is the time when the upper rim of the sun appears on the horizon in the morning.

Civil Twilight:Morning civil twilight begins when the geometric center of the sun is 6^o below the horizon and ends at sunrise.  Evening civil twilight begins at sunset and ends when the geometric center of the sun is 6 degrees below the horizon. Under these conditions absent fog or other restrictions, the brightest stars and planets can be seen, the horizon and terrestrial objects can be discerned, and in many cases, artificial lighting is not needed.

Nautical Twilight:Begins in the morning, or ends in the evening, when the geometric center of the sun is 12^o below the horizon.  In general, the term nautical twilight refers to sailors being able to take reliable readings via well-known stars because the horizon is still visible, even under moonless conditions.  Absent fog or other restrictions, outlines of terrestrial objects may still be discernible, but detailed outdoor activities are likely curtailed without artificial illumination.

Astronomical Twilight: Begins in the morning, or ends in the evening, when the geometric center of the sun is 18^o below the horizon.  In astronomical twilight, sky illumination is so faint that most casual observers would regard the sky as fully dark, especially under urban or suburban light pollution. The horizon is not discernible and moderately faint stars or planets can be observed with the naked eye under a non-light polluted sky.  Point light sources such as stars and planets can be readily studied by astronomers under astronomical twilight but not galaxies, nebula, and globular clusters.

Dawn: is technically defined as the period between the start of civil twilight and sunrise.

 

Sunrise, and onset of civil and nautical twilight times for Hopewell Junction, NY, USA are plotted below.

 

Location: Hopewell Junction, NY, USA.

Latitude: 41^o35′3″ N, Longitude: 73^o48′31″ W

Year: 2023

Time Zones: Eastern Standard Time (EST)
Eastern Daylight Time (EDT) from March 12^th, 2023, to November 5^th, 2023

Fig. A2 Sunrise and onset of civil and nautical twilight times in Hopewell Junction, NY, USA for 2023.

Fig. A3 Sunrise and onset of civil and nautical twilight times in Hopewell Junction, NY, USA from vernal equinox to autumnal equinox.

Time difference in minutes between sunrise and civil and nautical twilight onset times is shown in Fig. A4. Civil twilight begins 25 to 32 minutes before sunrise. Nautical twilight begins between 58 and 78 minutes before sunrise.

Fig. A4 Time difference (in minutes) between sunrise and onset of civil and nautical twilights.

Light Intensity Measurements

Light intensity was recorded in each Quarter using a light meter (Dr.meter model LX1330B) with a resolution of 0.1 Lux and a measurement accuracy of +/- 3%. This standard light meter measures incident light, wavelength-weighted by the luminosity function defined as the average spectral sensitivity of human visual perception for brightness. Different bird species and individual birds within a species may perceive brightness differently - an unknown factor.

The sensor was held in a vertical position against a windowpane facing part of the sky and trees. There were no artificial lights in the vicinity, but scattered city lights had some influence on the pre-dawn brightness.

Fig. A5 Measured light intensity in each Quarter before and after sunrise.

Figure A5 shows the light intensity measured once in each Quarter each day. The dashed lines are hand drawn to indicate the maximum light intensity before sunrise. The increase in light intensity with time before sunrise is exponential, the slope decreases after sunrise. Clouds, rain, haze and fog may reduce the light level in a Quarter by as much as a factor of 20. The light intensity in Q5 and Q4 was < 0.1 Lux and not detected by the meter. The first measurement of the day was made in Q3 (30 to 45 minutes before sunrise) when the light intensity was in the 0.1 to 1.0 Lux range.

Figure A6 illustrates how the light intensity levels in Q1 and Q2 track with Q3 on three days with different sky conditions. On clear and cloudy days, the tracking is good and the intensity at Q4 is extrapolated to ≤ 0.1 Lux. During a rainstorm, the light intensity may be more variable at dawn as the rain and cloud cover change over time.

 

Fig. A6 Measured light intensity in Q1, Q2 and Q3 on three days with different sky conditions: 1) clear, 2) cloudy, 3) rain.

Light intensity on a clear moonless night is reported> to be 0.002 Lux, 0.05 Lux on a full moon night and 3.5 Lux at the onset of civil twilight on a clear new moon night. The highest measured intensity in Q2, 8 minutes after the onset of civil twilight on July 31^st with a full moon, was 18 Lux. Using the slope of the red line of June 19^th in Fig. A6, the maximum light intensity at the onset of civil twilight is then 7.7 Lux, twice the reported value. Also, from the slope of this line we can deduce that a 16X change in Q2 light intensity would have shifted the StartTime of a robin by 17 minutes, if the singing were triggered by light intensity as measured by the light meter. However, as shown in Fig. 6 (reproduced below), the StartTime of a robin remained 52 +/- 3 minutes as the light intensity in Q2 changed from 1.0 Lux to 16.2 Lux.

Fig. 6 StartTimes of American Robin from sunrise vs. light intensity in Quarter Q2. Time for sunrise, shown as orange line, is designated as zero.

Appendix B: Dawn Participants

Songbirds participating in the dawn chorus; resident term, body mass, total number of Quarters and first and last dates heard are listed in Table 4.

Table 4 Songbirds participating in dawn chorus from March 24^th, 2023 to September 9^th, 2023. Note resident term abbreviations: A = All year, S = Summer, W = Winter

 

	Species	Resident Term	Body Mass (g)	# of Quarters Heard	First Heard	Last Heard
1	American Robin	A	77	461	24-Mar	9-Sep
2	Northern Cardinal	A	45	405	24-Mar	9-Sep
3	Carolina Wren	A	21	177	24-Mar	8-Sep
4	Tufted Titmouse	A	21.5	146	27-Mar	26-Aug
5	House Finch	A	21.1	119	27-Mar	4-Aug
6	Black-capped Chickadee	A	11	96	12-Apr	9-Sep
7	Blue Jay	A	85	81	10-Apr	9-Sep
8	White-breasted Nuthatch	A	21.2	60	18-Apr	9-Sep
9	American Goldfinch	A	13	49	26-Apr	3-Sep
10	American Crow	A	450	45	29-Mar	12-Aug
11	Song Sparrow	A	20.1	38	25-Mar	10-Jun
12	Eastern Bluebird	A	31	31	31-Mar	7-Sep
13	Red-winged Blackbird	A	52	25	3-Apr	4-Aug
14	Northern Mockingbird	A	49	11	13-Jun	2-Sep
15	Common Grackle	A	115	10	16-Apr	14-Jul
16	Fish Crow	A	280	4	26-May	18-Jun
17	House Sparrow	A	28	2	15-Apr	1-Aug
18	European Starling	A	82	1	28-May	28-May
19	Brown-headed Cowbird	A	44	1	21-May	21-May
20	Chipping Sparrow	S	12	339	-Apr	5-Aug
21	Eastern Wood-Pewee	S	14	87	17-May	4-Sep
22	House Wren	S	11.1	77	2-May	22-Aug
23	Gray Catbird	S	37	75	9-May	9-Sep
24	Eastern Phoebe	S	20	48	12-Apr	2-Sep
25	Baltimore Oriole	S	33	9	11-May	21-Aug
26	Barn Swallow	S	19	9	22-May	21-Aug
27	Eastern Kingbird	S	40	7	28-Jun	30-Jul
28	Great Crested Flycatcher	S	34	6	31-May	14-Aug
29	Warbling Vireo	S	12	3	21-Jun	24-Jun
30	Red-eyed Vireo	S	17	2	17-Jun	18-Jun
31	Tree Swallow	S	20.2	2	8-May	21-May
32	Yellow Warbler	S	9.5	1	17-Jun	17-Jun
33	Eastern Towhee	S	40	1	30-Apr	30-Apr
34	Wood Thrush	S	47	1	1-Aug	1-Aug
35	White-throated Sparrow	W	26	20	12-Apr	15-May
36	Dark-eyed Junco	W	19.1	13	24-Mar	14-Apr
37	Ruby-crowned Kinglet	W	6.5	1	16-May	16-May

 

Acknowledgment

We thank Dr. Mark B. Ketchen for carefully reviewing the data analysis and for making valuable comments on the manuscript.

References

1.       Horace W. Wright (1913) "Morning Awakening and Even-song"  The Auk , Oct., 1913, Vol. 30, No. 4 (Oct., 1913), pp. 512-537. https://www.jstor.org/stable/4072050

2.       Kroodsma Donald (2020) "Energized Dawn Singing" in 'Birdsong for the Curious Naturalist', Chapter 7, Houghton Miffliin Harcourt Publishers, pp 112-123.

3.       Diego Gil and Diego Llusia (2020) "The Bird Dawn Chorus Revisited", Chapter 3 in 'Coding Strategies in Vertebrate Acoustic Communication', Springer.

4.       Thomas Robert J. et. al. (2002) "Eye size in birds and the timing of song at dawn" Proc. Royal Society London, vol 269, pp. 831-837.

5.       Miller Mark W. (2006) "Apparent effects of light pollution on singing behavior of American Robins" The Condor vol.108, pp 130-139.

6.       Bruni A. et. al. (2014) "Dawn chorus start time variation in a temperate bird community: relationships with seasonality, weather and ambient light" J. Ornithology, 155:877-890.