Monday, July 17, 2017

Leach's Storm-Petrels on Little White Island

On July 14, 2017, Keith Lowe and I left by Zodiac from Marie-Joseph, a little village east of Ecum Secum, and made a quick stop at Gull Rock then landed on Little White Island.

Alix d'Entremont (me) holding a Leach's Storm-Petrel on Little White Island, Halifax County. Photo by Keith Lowe.
Again this year I am doing colonial seabird surveys for Environment Canada and wanted to check the islands in the Eastern Shore Island Wilderness Area that were recorded as having the most Leach's Storm-Petrel colonies. Little White Island was last surveyed in 1981 when 616 pairs were recorded.

Location map of Little White Island, Halifax County. Bing Map.
Our anchoring area on the western side of Little White Island. Photo by Alix d'Entremont.

We landed on the western end of Little White Island and found that there were quite a few. Considering the size of the island (350 m by 100 m) and the density of the burrows, we decided to follow the sample method described in Colonial Waterbird Monitoring Program: A Surveyor's Guide previously provided to me by Environment Canada. We sampled 5 areas that were representative of the different vegetation types and slopes on the island. The sample areas were squares with side dimensions of about 4 paces or 3.3 m which equates to an area of 10.9 m². We also noted the general densities to allow for better generalizations of densities by habitat type throughout the island.

Location of Sample 1, short grass, on Little White Island. Photo by Alix d'Entremont.
Below is the field data and key and the data for the 5 samples.

A = Adult
E = Egg
C = Chick
CRE = Can't Reach End
REN = Reached End, Nothing

Sample 1 - Short Grass, slight slope.
44° 53.657' N, 62° 6.093' W
6 burrows (A,E; A; A; CRE; CRE; REN).

Sample 2 - Short Grass, slight slope, near possible fox den.
44° 53.631' N, 62° 6.032' W
0 burrows.

Sample 3 - Tall Vegetation, slight slope.
44° 53.626' N, 62° 5.899' W
0 burrows.

Sample 4 - Short Grass, moderate slope.
44° 53.649' N, 62° 5.871' W
3 burrows (CRE; CRE; CRE).

Sample 5 - Short Vegetation, large slope.
44° 53.660' N, 62° 5.966' W
13 burrows (CRE; A; A; REN; CRE; E; CRE; A; CRE; REN; CRE; CRE; CRE).

Sample 5 had the highest density of all samples and this density of holes appeared to be consistent through the entire north slope. The sample was taken near the middle of the slope both east-west and north-south and was at an entirely random, central location.

The north slope of Little White Island, near the location for sample 5. Photo by Keith Lowe.

I roughly classified the entire island by habitat type in Google Earth and added the sample locations. The burrow calculation for each habitat type was calculated using a burrow density that I chose based on the sample points and the general feeling that I got while walking through the habitat and noting the number of burrows compared to the sample plots.

Sample points and habitat type on Little White Island. Google Earth Export.
Short Grass @ 3,500 m² (3 burrows per 10.9 m² = 0.275 burrows per m²)
3,500 m² * 0.275 burrows per m² = 960 burrows

Short Grass @ 12,500 m² (1 burrow per 10.9 m² = 0.09 burrows per m²)
12,500 m² * 0.09 burrows per m² = 1,145 burrows

Short Vegetation @ 6,600 m² (8 burrows per 10.9 m² = 0.734 burrows per m²)
6,600 m² * 0.734 burrows per m² = 4,844 burrows

Total number of burrows = 6,949 burrows.

Obviously this estimate is simply that - an estimate. Given that there were only two people doing the survey, we weren't able to cover the island in detail, but this at least gives us an idea of the size of the colony. For a more accurate estimate, I would delineate the habitat types and slopes by GPS on the ground and take 4 to 6 samples in each habitat type and slope combination. This should result in a better estimate of numbers.

We did see at least 2 burrows and 1 adult that were predated and a few larger burrows and piles of crushed crustacean shells.

Large burrows and mounds of what appeared to be crustacean shells on Little White Island. Photo by Alix d'Entremont.
Predated adult on Little White Island. Photo by Alix d'Entremont.

The Leach's Storm-Petrel colony on Little White Island was by far the largest that I've ever been to on a grassy island. I have visited Bon Portage that was estimated to have had 50,000 pairs, but it is a wooded island. These storm-petrel colonies are much harder to detect that other colonial birds, so I'm sure there are other large colonies around the province. I hope to get to Indian Island near LaHave in the next few weeks to check for storm-petrels.

1 comment:

  1. That was an awesome day on the ocean Alix. Great work with the analysis.