Black Rails were photographed in 86% of arrays (n = 14, Table 1) and 80% of wetlands (n = 4) during 2017 – 2019. Sampling effort during this period totaled 46,033 camera trap days and resulted in a total of 2,040,536 photographs, 30,841 (1.5%) of which contained Black Rails.
Brood Size
In broods documented within six days of hatching, brood sizes ranged from a minimum of one chick to seven chicks (x̄ = 3.4 ± 1.8 SD, n = 16). For chicks > ten days old when initially detected, we did not estimate brood size because chicks ventured farther from parents and siblings after frequent brooding was no longer required.
Chick Development
We documented the rate of chick development and characterized key physical and behavioral developmental stages (Tables 2 and 3) of broods photographed repeatedly between hatching and fledgling. Age was calculated based on chicks remaining in the nest for approximately 24 hours (Davidson 1992) and the developmental stage of the chicks photographed. Fledging occurred at approximately 40 days after hatching. In several instances, development within broods was asynchronous, resulting in a difference in fledging dates as great as three days among siblings.
Breeding Phenology
Black Rail chicks were photographed between May and September during 2015 – 2019 (Fig. 1). Estimated hatch dates ranged from 13 May – 20 August (x̄ = 1 July ± 30.0 SD, n = 33; Table 4), suggesting incubation occurred between April and August based on an approximated 26 day period between the initiation of egg laying and hatching (Flores and Eddleman 1993; Legare and Eddleman 2001; U.S. Fish and Wildlife Service 2018). In arrays where vegetation growth was delayed by fire during February, the mean estimated hatch date was 18 July (± 28.1 SD, n = 9) compared to 25 June (± 30.8 SD, n = 24) in arrays not burned. At least one chick survived to 15 days post-hatching in a minimum of 30 broods, and fledging was confirmed for eight broods. We did not determine if chicks from the remaining 25 broods fledged, however based on hatch dates and a period of 40 days between hatching and fledging, we estimated potential fledging dates ranged from 23 June to 30 September (x̄ = 10 August). Fledglings were photographed on 27 June 2017, between 16 July and 7 September 2018, and between 11 August and 7 October 2019.
Flightless Molt Phenology
Flightless molt (Fig. 2) was documented in Wetlands 1 and 2 during the 2015 – 2016 pilot study and in Arrays 1a, 1b and 2d in 2018 and Arrays 1b and 2a during 2019. The duration of molt was approximately 21 days from the initiation of primary feather loss to the completion of primary feather regrowth. We observed ten flightless adults. In the three instances when pairs were documented molting, the paired adults molted nearly simultaneously with the females beginning two to three days later compared to males. Molt initiation dates ranged from 15 August to 20 September (x̄ = 30 August ± 14.0 SD, n = 10; Table 5), with estimated molt completion between 5 September and 11 October.
Behavioral Observations
Courtship behaviors (Fig. 3) included offering food (n = 11 male to female, n = 1 female to male), allopreening (n = 7 male preening female, n = 1 female preening male), and pursuit of the female by the male (n = 25). Throughout the study, we documented seven copulations. During one copulation, adult male and female Black Rails were simultaneously photographed and filmed (Fig. 4). Concluding copulation, the male tumbled from the female and circled her while walking with a lowered head and raised wings. As the male circled, the female bowed forward with raised tail feathers then ruffled her feathers before beginning to preen. Throughout the study, this raised wing display by males was observed following three copulations and females were observed ruffling feathers and preening following four copulations. Males closely pursued females prior to five copulations.
In seven instances during the study, two or more broods were photographed in the same array during a single breeding season. Copulations occurred while young chicks were present in arrays during two such instances. Following copulation on 5 June 2017 in Array 2a, described above, adults departed then returned to the same location 53 minutes later with downy chicks. On 18 July 2017, downy chicks from a second brood were documented in the array. Estimated hatch dates for the first and second broods were 41 days apart. The estimated hatch date for a third brood in the array was 34 days after the hatch date for the second brood.
During 2019, four broods were documented in Array 1b. It is feasible that a single pair hatched the first and third broods or second and fourth broods, however, the number of days between estimated hatch dates for the first and second broods and the third and fourth broods were 23 and 14 days apart, respectively. The breeding phenology within Array 1b suggests breeding territories of two or more pairs overlapped within the camera array. Chicks from different broods were observed in close proximity to each other. On 30 August 2019, a ten day old chick from the fourth brood closely following an adult appeared in the same photograph as a partially feathered chick presumably from the third brood in the array. Chicks from both broods continued to be photographed in the array throughout September.
We documented 57 interactions between adult Black Rails and their chicks (Fig. 5). During these interactions, both adults (n = 7), a male (n = 22), a female (n = 12), or an adult of unknown sex (n = 16) were present. The most frequently observed chick-adult behaviors were chick(s) following an adult (n = 49), being brooded (n = 11), being fed (n = 7), and being preened (n = 1) (Fig. 5). We observed multiple behaviors during 14 interactions. Chicks solicited brooding and feeding by adults by bowing, fluttering their wings and vocalizing. Broods of downy chicks were frequently observed in a group sitting on the ground and preening themselves, and siblings occasionally pecked each other. Young continued to be observed within natal territories beyond fledging but were not observed receiving parental care after 25 days post-hatching. Although most chicks over 25 days old were alone in photographs, we observed two chicks from one brood brooding each other at 26 days and allopreening at 37, 38, and 39 days. Their allopreening behavior closely resembled allopreening courtship behavior between adults.