Inter-observer agreement
Mean Cohen’s Kappa statistic measuring the inter-observer agreement for observations on mallards was 1.00 (s.d.: 0; range: 1–1) based on 17 observation days. For observations on other wild birds, mean Cohen’s Kappa was 0.994 (s.d.: 0.027: range 0.89–1) based on 17 observation days with these birds present. Disagreement was present in only one wild bird observation on a given day where some White wagtails (Motacilla alba) were missed by one of the observers.
General observations
Mallards ((Anas platyrhynchos) visited the free-range study area without the laser in operation between just after sunset (when the layers were already back into the poultry barn) and sunrise. Western barn owls (Tyto alba) hunted in the free-range study area on mice and rats during the night. Blackbirds (Turdus merula), Western yellow wagtails (Motacilla flava), White wagtails (Motacilla alba), Common Moor-hen (Gallimula chloropus) and Common kestrels ( Falco tinnunculus)) visited the free-range study area limited to the period after sunrise in the morning until 10:00 AM without the laser in operation. When the layers would flow out of the poultry barn and into the free-range study area at around 10:00 AM, these wild birds would disappear, scared by the large amount of layers in the free-range study area. It was expected to have a number of gulls of different species present in the free-range study area in the morning between sunrise and 10:00 AM. They were not observed this time, but were seen present in the surrounding pastures in the time period that the laser was operational in the free-range study area and at the same time not sweeping in the surrounding pastures.
Without the laser in operation, mallards (Anas platyrhynchos) visited the free-range study area of the poultry farm on 28 out of 29 observation days, while with the laser in operation, mallards visited the free-range study area on 1 out of 28 observation days (Fig. 5), which is a highly (p < 0.001) significant reduction in the number of days mallards visited the free range. Furthermore, without the laser in operation, other birds (Blackbird (Turdus merula), Western yellow wagtail (Motacilla flava), White wagtail (Motacilla alba), Western barn owl (Tyto alba), Common Moor-hen (Gallimula chloropus) and/or Common kestrel (Falco tinnunculus)) visited the free-range study area on 18 out of 29 observation days, while with the laser in operation, other birds visited the free-range study area on 4 out of 28 observation days (Fig. 4), which is a highly (p < 0.001) significant reduction in the number of days these wild birds visited the free range area.
Daily rate of wild birds visiting
A summary of descriptive statistics on daily rate of wild birds visiting the free range study area with and without the laser in operation, grouped by taxonomic Order, are shown in Table 1. Wild birds of the Order Anseriformes, in this case only mallards (Anas platyrhynchos), visited the free-range study area often and with considerable day-to-day variation in the period without the laser in operation while virtually no mallards were observed in the period with the laser in operation (Fig. 5). A similar effect of the laser can be observed for visiting wild birds of the Orders Passeriformes, Strigiformes, Gruiformes and Falconiformes, although the number of visits are considerably smaller compared to those by the mallards (Fig. 5).
Table 1
Summary of daily number of wild birds visiting during the experimental periods (28 observation days with and 29 days without the laser in operation), grouped by taxonomic Order, observed in the free range study area.
Order
|
Laser present
|
Median
|
Min
|
Max
|
Anseriformes
|
No
|
10
|
0
|
29
|
|
Yes
|
0
|
0
|
1
|
Passeriformes
|
No
|
4
|
0
|
30
|
|
Yes
|
0
|
0
|
4
|
Falconiformes
|
No
|
0
|
0
|
0
|
|
Yes
|
0
|
0
|
1
|
Gruiformes
|
No
|
0
|
0
|
1
|
|
Yes
|
0
|
0
|
0
|
Strigiformes
|
No
|
0
|
0
|
1
|
|
Yes
|
0
|
0
|
0
|
The mean daily rate of wild birds (all species) visiting was significantly (p < 0.001) lower when the laser was used: RR = 0.0183 (95% CI: 0.007–0.043), which means that with the laser in operation, the mean rate of wild birds (all species) visiting is 55 (1/0.0183) times lower than when the laser is not in operation.
Daily rate of wild birds visiting by taxonomic Order
The mean daily rate of wild birds of the Order Anseriformes visiting the free-range study area was significantly (p < 0.001) lower when the laser was used: RR = 0.00327 (95% CI: 0.00018–0.0159), which means that with the laser in operation, the mean rate of wild birds of the Order Anseriformes visiting was 306 (1/0.00327) times lower than when the laser is not in operation. Furthermore, the mean daily rate of wild birds of the Order Passeriformes visiting was significantly (p < 0.001) lower when the laser was used: RR = 0.0394 (95% CI: 0.0149–0.0919), which means that with the laser in operation, the mean rate of wild birds of the Order Passeriformes visiting was 25 (1/0.0394) times lower than when the laser is not in operation. To estimate the RR for birds of the Orders Falconiformes, Gruiformes and Strigiformes, they were combined into one group because of their low number of daily visits. The mean daily rate of wild birds of the Orders Falconiformes, Gruiformes and Strigiformes together visiting was about 4 times (not significant, p = 0.22) lower when the laser was used: RR = 0.256 (95% CI: 0.0129–1.7689).
A stone marten (Martes foina) family – with a burrow in the middle of the free-range study area - and numerous unspecified species of mice and rats appeared daily during the night in the free-range study area. The laser had no influence whatsoever on the daily rate of visiting by these mammals.
Laser efficacy
The estimated RRs were used to calculate the percent efficacy of the laser for reducing the rate of wild birds visiting. The overall (all bird species) efficacy of the laser for reducing the rate of wild birds visiting was 98.2 % (95% CI: 95.7–99.3). The estimated efficacy of the laser for reducing the rate of wild birds visiting for each taxonomic Order was: 99.7 % (95% CI: 98.4–99.98) for birds of the Order Anseriformes, 96.1 % (95% CI: 90.8–98.5) for the birds of the Order Passeriformes and 74.4 % (95% CI: 0–98.7) for birds of the Orders Falconiformes, Gruiformes and Strigiformes together.
Exposure time of free-range study area to wild birds
A summary of descriptive statistics on exposure time of the free-range study area to visiting wild birds with and without the laser in operation, grouped by taxonomic Order, are shown in Table 2. The overall exposure time (all bird species) was significantly (p < 0.001) lower when the laser was used: RR = 0.00162 (95% CI: 0.000295–0.0089), which means that with the laser in operation, exposure time was 617 (1/0.00162) times lower than when the laser was not in operation.
Table 2
Summary of daily exposure time (in min.) of free-range study area to wild birds. This is a combination of the number of birds visiting daily and the duration of their visit during the experimental periods (28 observation days with and 29 days without the laser in operation), grouped by taxonomic Order.
Order
|
Laser present
|
Median time
|
Min
|
Max
|
Anseriformes
|
No
|
2144.21
|
15.80
|
15323.45
|
|
Yes
|
1.25
|
1.25
|
1.25
|
Passeriformes
|
No
|
31.75
|
0.37
|
253.43
|
|
Yes
|
4.43
|
1.00
|
5.05
|
Falconiformes
|
Yes
|
0.45
|
0.45
|
0.45
|
Gruiformes
|
No
|
1.88
|
1.88
|
1.88
|
Strigiformes
|
No
|
2.68
|
0.70
|
27.83
|
Exposure time to wild birds of the Order Anseriformes was significantly (p < 0.001) lower when the laser was used: RR = 0.000431 (95% CI: 0.0000246–0.00756), which means that with the laser in operation, exposure time of wild birds of the Order Anseriformes was 2,320 (1/0.000431) times lower than when the laser is not in operation. Furthermore, exposure time to wild birds of the Order Passeriformes was significantly (p < 0.001) lower when the laser was used: RR = 0.0575 (95% CI: 0.0129–0.2566), which means that with the laser in operation, exposure time of wild birds of the Order Passeriformes was 17 (1/0.0575) times lower than when the laser is not in operation.
To estimate the RR with respect to exposure time for birds of the Orders Falconiformes, Gruiformes and Strigiformes, they were combined into one group because of their low number. Exposure time to wild birds of the Orders Falconiformes, Gruiformes and Strigiformes together was 18 times (1/0.0544; not significant, p = 0.14) lower when the laser was used: RR = 0.0544 (95% CI: 0.00115–1.04175).
Observations by farmer in surrounding pastures
Since there was no VCRS monitoring in the surrounding pastures, we could only rely on anecdotal daily observations by the poultry farmer. He indicated that without the laser in operation in the pastures, sometimes large congregations of geese (barnacle goose (Branta leucopsis), greyleg goose (Anser anser), greater white-fronted goose (Anser albifrons), gulls (lesser black-backed gull (Larus fuscus), black-headed gull (Chroicocephalus ridibundus) and occasionally some swans (mute swan (Cygnus olor)) were observed to be present. With the laser in operation, the pastures were swept clean: no geese, gulls or swans were observed by the poultry farmer anymore during daytime.