We estimated an island-wide minimum abundance of 10,512 rose-ringed parakeets in January 2020 (prior to roost culling) among the three known roosts (Lihue_1, Poʻipū, and Kapa‘a; Table 1). An estimated 6,030 parakeets were removed via roost culling with 4,415 carcasses retrieved from March 2020 – March 2021. Among all culling efforts, there was as estimated mean of 44.7 (SD = 28.4) parakeets removed per shooter hour. An average of 36.7 (SD = 22.9) carcasses were retrieved per shooter hour (Table 2). Island-wide minimum abundance estimate were 4,963 individuals in November 2020, 6,883 in February 2021, and 7,372 in April 2021 (Table 1). The number, location, and estimated abundance of roosts changed throughout the study.
Table 1
Estimates of island-wide minimum abundance of rose-ringed parakeets (Psittacula krameri) on Kaua‘i, Hawai‘i, USA, estimated via roost counts. Roost counts were conducted two to four times at each site within a two-week period; reported estimates represent averages from the respective time period. Periods indicate the roost was not occupied during the study period.
Roost | January 2020 | November 2020 | February 2021 | April 2021 |
Kapa‘a | 1,501 | 1,911 | 1,657 | 1,358 |
Lihue_1 | 2,559 | . | . | . |
Lihue_2 | . | 880 | . | 1,317 |
Lihue_3 | . | . | 1,031* | . |
Poʻipū | 6,452 | 1,325 | 3,043 | 4,650 |
Koloa | . | 847 | 1,152 | . |
Princeville | . | . | . | 47 |
Total | 10,512 | 4,963 | 6,883 | 7,372 |
*estimate prior to February 2021 roost culling at the Lihue_3 roost; an estimated 725 birds were located at Lihue_2 after roost culling. |
Table 2
Estimated number of rose-ringed parakeets (Psittacula krameri) culled and carcasses retrieved from roost culling efforts on Kaua‘i, Hawai‘i, USA.
| Total | Phase 1 | Phase 2 | Phase 3 |
March – April 2020 (Lihue_1 & Poʻipū) | May 2020 (Poʻipū) | June – November 2020 (Poʻipū) | February - March 2021 (Lihue_3 & Koloa) |
Nights of culling | 30 | 9 | 12 | 6 | 3 |
Estimated parakeets culled | 6,030 | 1,511 | 3,415 | 392 | 712 |
Carcasses retrieved | 4,415 | 1,277 | 2,333 | 238 | 567 |
Mean estimated take per shooter hour (SD) | 44.7 (28.4) | 53.8 (25.9) | 56.25 (23.7) | 22.2 (29.6) | 28.1 (16.6) |
Mean carcasses retrieved per shooter hour (SD) | 36.7 (22.9) | 49.6 (19.9) | 39.4 (17.1) | 19.5 (29.1) | 22.6 (15.3) |
Phase 1: March – May 2020
Over 21 nights of culling, an estimated 4,926 rose-ringed parakeets were removed from the Lihue_1 and Poʻipū roosts, a confirmed 3,619 carcasses were retrieved, and average take per shooter hour was 55.0 (SD = 23.5). At the Lihue_1 roost, an estimated 561 parakeets were removed (530 carcasses retrieved) over four nights of culling, approximately 22% of the pre-culling roost abundance (n = 2,559; Table 1). During the fourth night of culling, the number of birds removed per shooter hour decreased substantially (13.1) from the average of the first three nights (59.8), as the parakeets had partially abandoned the roost (J. Young, Kani Wildlife Control, personal communication). After the fourth night of culling, the parakeets fully abandoned the roost.
An estimated 4,365 parakeets were removed from the Poʻipū roost - approximately 68% of the pre-culling roost abundance (6,452; Table 1) - and 3,089 carcasses were retrieved. Average take per shooter hour was 57.0 (SD = 18.6). Over the 17 nights of culling, the parakeets did not fully abandon the roost. While we did not measure the number of birds per tree or per individual property, we noted that the extent and composition of the roost changed. For example, during this period, the parakeets shifted approximately 175 m west onto a different property. In many areas, the parakeets shifted to private properties where culling was not permitted (J. Young, Kani Wildlife Control, personal communication).
Of the 2,993 carcasses evaluated, 653 (21.8%) were sexually mature males. Of the 585 carcasses necropsied, 142 were immature males, 123 were mature females, and 320 were immature females (Table 3). Using these findings to estimate the total samples size, we estimated the 4,926 parakeets removed during Phase 1 included 21.8 ± 3.4% mature males, 19.0 ± 3.2% immature males, 16.4 ± 3.0% mature females, and 42.7 ± 4.0% immature females (Figure 2).
Figure 2. Estimated number and percent (95% CI) of rose-ringed parakeets (Psittacula krameri) by age and sex removed via roost culling from March - April 2020 (n = 1,511 from Lihue_1 and Poʻipū roosts), May 2020 (n = 3,415 from Poʻipū roost), and February 2021 (n = 498 from Lihue_3 roost) on Kaua‘i, Hawai‘i, in 2020 and 2021. We identified all mature males by plumage, whereas we identified a sample of mature females, immature females, and immature males via necropsy during Phase 1 (n = 337 from March – April; n = 248 from May) and Phase 3 (n = 52). Carcasses were not evaluated during Phase 2 due to COVID-19 travel restrictions.
Phase 2: June – November 2020
An estimated 392 rose-ringed parakeets were culled (238 retrieved carcasses) at the Poʻipū roost. The average number of parakeets removed per shooter hour in Phase 2 (22.2 [SD = 29.6]; Table 2) was lower than Phase 1 and ranged from 7.8 to 13.7 in June–August. After an 85-day hiatus in culling, the number of birds removed per shooter hour increased in November to 82.3 (Figure 3). We were unable to evaluate age and sex of carcasses retrieved during this time due to COVID-19 travel restrictions.
We estimated the island-wide minimum abundance was 4,963 individuals among four roosts in November 2020 after the conclusion of Phase 2 roost culling. Given the Lihue_1 roost was abandoned during roost culling, there were no birds in this location. The Poʻipū roost was greatly reduced in size due to culling and partial roost abandonment. The Kapa‘a roost, where no culling occurred, had increased by approximately 27%. Two roosts had established, Lihue_2 and Koloa; it was unknown when the Lihue_2 roost established, but the Koloa roost was first documented in June 2020 (Figure 1; Table 1; W. Bukoski, personal observation). While neither roost was present in January 2020, both were historic roost locations that had previously been abandoned for unknown reasons.
Figure 3. Estimated number of rose-ringed parakeets (Psittacula krameri) culled per shooter hour (black dots) and total number of carcasses retrieved per shooter hour (gray dots) at the Poʻipū roost in 2020 (Phases 1 and 2) on Kaua‘i, Hawai‘i, USA, in 2020 and 2021. Data were not reported by the independent wildlife control company for three of the 23 nights included in this time period (May 21, 22, and 29).
Phase 3: February & March 2021
Between November 2020 and February 2021, the Lihue_2 roost abandoned for unknown reasons and the Lihue_3 roost became established (Figure 1). Among the four known roosts in February 2021, we estimated island-wide minimum abundance to include 6,883 rose-ringed parakeets (Poʻipū, Lihue_3, Kapa‘a, and Koloa; Table 1).
We estimated the Lihue_3 roost had 1,031 birds prior to culling. On 23 February 2021, an estimated 350 rose-ringed parakeets were culled (298 retrieved carcasses). We estimated 680 parakeets were occupying the Lihue_3 roost on the morning of 24 February. On 24 February an estimated 148 parakeets were culled (103 retrieved carcasses). We counted only 14 parakeets at the roost on the morning of 26 February, indicating the site had been abandoned. Between the two nights of culling, an estimated 48.3% of the roost was culled prior to abandonment.
Of the 402 carcasses retrieved, 185 (46.0%) were mature males. Of the 52 birds of unknown age and sex necropsied, we identified 28 mature females, nine immature females, and 15 immature males (Table 3). Using these observations, we estimated take from the Lihue_3 roost during this period included 29.1 ± 3.7% sexually mature females, 15.6 ± 2.9% immature males, and 9.3 ± 2.4% immature females (Figure 2). Qualitatively, we observed that follicles were more developed among females in February 2021 than March–May 2020, including one female with an intact egg.
During the single night of culling at the Koloa roost, an estimated 214 individuals were removed (165 retrieved carcasses). The parakeets did not return the following evening, indicating they abandoned the site after only one night of culling. An estimated 18.6% of the roost was removed prior to abandonment.
Table 3
Observed age and sex of rose-ringed parakeets (Psittacula krameri) removed via roost culling on Kaua‘i, Hawai‘i, USA, in March - May 2020 (n = 2,993, Phase 1) and February 2021 (n = 402, Phase 3). We identified all mature males by plumage, whereas we identified a sample (n = 585, Phase 1; n = 52, Phase 3) of mature females, immature females, and immature males via necropsy. Carcasses were not evaluated during Phase 2 due to COVID-19 travel restrictions.
| Phase 1 | Phase 3 |
| March – April 2020 | May 2020 | February 2021* |
Mature Males | 313 | 340 | 185 |
Unknown Age/Sex (Not Necropsied) | 490 | 1,265 | 165 |
Immature Males | 68 | 74 | 15 |
Mature Females | 55 | 68 | 28 |
Immature Females | 214 | 106 | 9 |
Total | 1,140 | 1,853 | 402 |
*includes only individuals culled at the Lihue_3 roost |
Comparison of age/sex culled by season
The age and sex ratio of rose-ringed parakeets culled varied between the March–April 2020 (n = 1,140), May 2020 (n = 1,853), and February 2021 (n = 498) sampling periods (Table 3; Figure 2). The likelihood of harvesting a mature female vs an immature female, immature male, or mature male was significantly higher in February compared with March/April or May (p <0.01; Table 4).
Table 4
Multinomial logistic regression predicting proportion of mature females compared with mature males, immature females, and immature males culled via roost culling on Kaua‘i, Hawai‘i, USA, over three time periods: March/April 2020 (n = 1,511), May 2020 (n = 3,416), and February 2021 (n = 499).
| Coefficient March/April | May | Standard error March/April | May | P-value March/April | May |
Mature Males | 0.38 | -0.66 | 0.14 | 0.12 | <0.01 | <0.01 |
Immature Females | 2.48 | 1.57 | 0.19 | 0.17 | <0.01 | <0.01 |
Immature Males | 0.83 | 0.70 | 0.17 | 0.15 | <0.01 | <0.01 |