2016 report

Skagway Arctic Terns 2016 report

The report below gives results of the 2016 Skagway Arctic Tern monitoring project.

It is also available as these 4 downloadable PDF files:

2016 Skagway Arctic Tern report

Appendix A - copy of 2015 press release

Appendix B - data

Appendix C - colony site map

References

[1] “Birds of North America, Arctic Tern” no.707, by Jeremy J. Hatch, 2002 (http://bna.birds.cornell.edu/bna/species/707/articles/introduction)

Executive Summary

Part of the colony accomplished reproduction in a short time period (2 months), indicating favorable conditions and low stress. Part of the colony required longer time periods (up to 3 months), which is associated with disturbances affecting the maturation process. Some breeding adults displayed mating behaviors mid-season, pointing to early failure or destruction of some scrapes or chicks.

Skagway's breeding terns were very tolerant of many kinds of frequent, predictable human disturbances. The terns reacted negatively to unusual and unpredictable human disturbances. Stationary objects (plastic owls, traffic cones) did not affect the terns. Terns sought shelter from harsh environmental conditions such as hot sun or high winds. Colony adults flushed in response to avian predators, while scrape spacing indicated that the colony was largely protected from land predators. Late in the season, internal disturbances were seen: other terns mobbing adults trying to feed chicks, and some adults showing hostile behavior toward late chicks.

Overall, the Ore Peninsula breeding colony was successful in 2016, but development time periods and late mating behavior indicate part of the colony was impacted by disturbances. The colony location is close to the prime fishing site at the mouth of the Skagway River. Human activities likely have a negative effect upon some terns, while at the same time evidence points to human disturbances providing a refuge from land predators for the colony.

Background

In June 2015, two unusual and severe human disturbances occurred at the known breeding colony at about the same time that birders noticed that terns abandoned the site. In July 2015, the Skagway Bird Club published a press release that describes the 2015 situation, summarizes Arctic Tern breeding biology, and presents the limited site-specific information available at the time for the Skagway breeding colony. (Appendix A)

Arctic Terns are protected under the Migratory Bird Treaty Act, which prohibits damaging the nests or young of breeding birds. In August 2015, the municipality of Skagway created a Migratory Bird Working Group to review the Arctic Tern situation and promote protection of all Skagway's migratory birds. The working group identified a need for better information on Skagway's breeding terns.

The Skagway Bird Club agreed to coordinate an effort to collect data in 2016 to better understand conditions at the breeding colony. The club created an open-structured, volunteer-based citizen science monitoring project that was implemented in April 2016. The Migratory Bird Working Group was disbanded in June 2016. The monitoring project continued to completion and is presented here.

Goals

This monitoring project was designed to answer 3 primary questions about Arctic Terns breeding in Skagway during 2016: where, when, and how many. More detailed secondary questions would also be examined if participants submitted enough optional data.

Primary goals:

Where: what areas on the Ore Peninsula were used by breeding terns?

When: when were terns present in the breeding colony area?

How many: what was the overall number of terns using the breeding colony?

Secondary goals, if sufficient data provided by participants:

Where were nests (scrapes) located, and what habitat characteristics did the terns prefer?

What was the reproductive development timing of the colony?

What disturbances were recorded, and how did the terns react to those disturbances?

Methods

Participation was open to all interested people, residents and visitors. Observers were invited to submit information through the Alaska eBird internet web portal or directly to Skagway Bird Club via email. Instructions for submitting data and a photographic guide for identifying developmental stages of Arctic Terns were posted on the SBC web site.

The minimum required information was:

• • • date

    • general location (eBird hotspot, if using eBird)

    • number of Arctic Terns observed

    • party size (number of people looking for terns)

    • all terns counted? yes/no (if not using eBird)

    • complete checklist? yes/no (if using eBird)

Participants were encouraged to add more information at their discretion, such as:

• • • time of day (start time)

    • duration of observation (elapsed time)

    • more specific locations of terns and/or nests (scrapes)

    • number of terns by developmental stage: eggs, chicks, chicks-in-transition, juveniles, immatures, adults

    • habitat characteristics

    • disturbances (human caused, environmental, natural predators)

    • behaviors (eBird breeding category; narrative descriptions)

In addition, a number of participants submitted photographs of terns at different developmental stages and engaged in different behaviors.

Results

Volunteer participants created a strong data set which addressed the three primary goals and permitted substantial examination of the secondary goals. The data are presented in Appendix B.

Twenty-two people submitted data – THANK YOU Volunteers !!!

A big THANK YOU also goes out to Temsco Helicopters for allowing the data collectors to place a traffic cone in the Temsco staging area when a late-nesting tern family occupied a site at risk for disturbance or damage from vehicles or people.

Primary Goal 1 : Where --- what areas on the Ore Peninsula were used by breeding terns?

In 2016, participants observed terns using a larger area on the Ore Peninsula than had been estimated in the 2015 map. Almost all observations were made from the vicinity of two eBird hotspots, the Ore Dock site and the Arctic Tern Colony site, or along Terminal Way (a private access road open to the public).

Tern nests, called scrapes because they are only a shallow depression made in the ground, and tern chicks were seen throughout the southern half of the colony area (blue shading on 2016 colony map). Terns also used the northern half of the colony area (orange shading on 2016 colony map), but parts of that area were blocked from direct observation.

Scrapes and chicks were seen on the ground in the western (left) side of the colony north area. Concrete barriers, structures, and restricted access zones blocked much of the eastern (right) side of the colony north area. However, patterns of flying terns landing and taking off from those areas, and perch locations of sentinel adults, indicated that some scrapes and chicks were present out of view.

The entire Ore Peninsula is part of a lease from the municipality of Skagway to PARN, the parent company of White Pass & Yukon Route Railroad. In turn, PARN has three subleasees that are affected by the breeding colony.

Petro Marine (pink) has an office, tank farm (large tank exclosure) and a fill station that is accessed by a gravel road outside their sublease. The gravel access road overlaps with the colony area.

AIDEA, the Alaska Industrial Development and Export Authority, (yellow) has a vacant lot, large concrete pad behind concrete barrier, truck access road, support buildings and parking area, small tank exclosure, and large material stockpile warehouse. All except the warehouse and support buildings overlap with the colony area.

Temsco Helicopters (green) has an office, helicopter yard with pads, and a separate staging area to the north. Only the staging area is part of the colony area.

Primary Goal 2: When --- when were terns present in the breeding colony area?

Arctic Terns were first seen in the Ore Peninsula area on 23 April 2016. They were last seen on 27 July 2016.

A trend curve fitted to the scatter of all 2016 tern counts (red dots) displays a shape consistent with a migratory bird breeding colony over the course of a reproduction season. The number of birds would be expected to slowly increase and reach a peak when most juvenile birds were still in the area. Then the bird counts would fall off rather quickly as adults and juveniles leave for their southerly migration.

The 2015 tern counts (black dots and gray shaded area) show a very different pattern. While counts are similar for both years during most of May, the 2015 terns were not seen in the area during most of June and July. A number of disturbances to the breeding colony were noted that year, particularly two unusual and severe disturbances of surface grading and gravel stockpiling.

For more information on the 2015 season, see Appendix A.

Primary Goal 3: How many --- what was the overall number of terns using the breeding colony?

Figure 3 shows the tern counts separated according to the two hotspot sites where most of the observations were collected. The data fall into three time periods that show different patterns of overall numbers of terns. These periods correlate with significant dates to give rough intervals of: incubation (May), chick rearing (June) and juvenile training (July). In actuality, these intervals were not neatly discrete, and observers recorded overlap between the developmental stages. However, the broad time periods allow reasonable estimates of the number of terns using the breeding area by focusing on the highest counts within the rough intervals.

During May, the consistent higher counts were of 20-25 terns. While incubating, one adult is almost always on the scrape (nest) and the partner adult may be on the ground nearby or away from the site fishing. Assuming about 20-40% of adults were out of view during this time, the number of breeding adults probably ranged from 30 to 40 terns, or about 15-20 pairs.

During June, the consistent higher counts were of roughly 60-80 terns. Once chicks were visible, they were included in total counts of terns, and the more they moved around the more likely they were to be seen. Also, as chicks matured, the probability of both parents flying at the same time increased. Some terns could have been fishing at sites out of view, which would depress the counts. There is also the possibility that migrating terns from sites to the north could stop for short times to feed at the river mouth, which would increase the counts.

During July, one high count of 70 terns was made at the Skagway River mouth. Parents and juveniles spent more time flying over the lower river and at river mouth area, perhaps because fishing conditions were easier for juveniles. This may be reflected in the slowly declining counts of terns seen at the Ore Dock Site and the Arctic Tern Colony Site. Also, flocks of adult & juvenile terns were noted swooping over the river upstream from the breeding area, where they would be difficult to view from these sites.

Secondary Goal 4: Where were nests (scrapes) located, and what habitat characteristics did the terns prefer?

Participants were not asked to map scrapes while collecting their data. However, some observers gave narrative descriptions of scrape locations with their data. After the season, participants were invited to mark a map with scrape locations that they could remember. All of this information was combined to produce the approximate scrape locations in Figure 4.

Not all scrapes produced chicks. Some scrapes likely represented a second attempt by breeding adult pairs. Some observed scrapes could be duplicate reports since their locations were not precisely mapped.

All inferred scrapes should be considered as suggestions. The ground was blocked from view at these locations, but perch locations of sentinel adults and tern flight patterns indicated that they were taking off and landing repeatedly from these areas.

Surfaces

Most scrapes were placed on gravelly or pebbly ground; relatively flat and open; with scattered sparse slightly larger rocks, twigs, and/or low vegetation. Some scrapes were also seen in areas with thicker vegetation.

A few scrapes were seen on the hardened surfaces in the AIDEA facility. These nests were made on paved or concrete substrates, usually located at a crack, at the edge of a depression, or some other interruption in the smoothness of the surface.

Surroundings

Many scrapes were located near a low structure on one side, such as a chainlink fence or concrete barrier, but with no obstructions on other sides. This orientation could indicate that a low structure on one side is desirable for defense against predators and protection from the elements, while keeping an open flight pathway for easy take-offs was also very important.Another important function of low structures nearby was perch sites for sentinel adults. These birds were often seen sitting on top of fences or concrete barriers, watching over incubating adults, eggs, or chicks.

No scrapes were seen within either tank exclosure: the large Petro Marine tank farm to the north, or the smaller AIDEA tanks midway. Tall structures close together, a surrounding low structure close by, or perhaps both together, may be undesirable because they interrupt open flight pathways.

Young chicks

Upon hatching, most young chicks took refuge near rocks, driftwood, or low vegetation in relatively open areas. Usually an adult was nearby. However, some small chicks were seen to hide in thicker vegetation near the chainlink fence. Other small chicks did not take advantage of nearby larger cover even when conditions were harsh.

A late season traffic cone was placed to protect a late nest from humans. It was also used by the two small chicks for wind and shade protection.

These observations suggest that having small chicks easily available to adults for feeding was desirable, while the chick's small size combined with the presence of a nearby adult usually gave adequate cover/protection from elements or predators.

Secondary Goal 5: What was the reproductive development timing of the colony?

In Figure 5, typical development time periods for maturation of eggs to chicks to juveniles ^[1] were compared to data from Skagway's Arctic Tern colony for 2016. The time periods were anchored to our first report indicating a breeding pair with scrape on 3 May.

The typical short range time period (top band) synchs with some of our data for both overall counts of terns (lines in top half of graph) and individual observations of eggs, chick and juveniles (points in bottom half of graph).

- Three dates with observations of eggs occur within the “incubate eggs” yellow time period of the short range.

- Some chick observations fall within the “hatch to fledge” orange time period of the the short range.

- Overall tern counts jump to higher numbers during the orange time period, which is when chicks and formerly incubating adults become more mobile and visible.

The juveniles observed in late June could indicate that some terns began the “occupy scrape” period before 3 May.

Some of our data lines up with the typical long range and disturbance bands. In particular, chicks were present for a much longer time period than any of the reference time periods. This suggests that disturbances affected the colony, which stretched out the total time periods needed for maturation.

In addition, some breeding adults can be expected to breed again if their first attempt is destroyed early in the season.^[1] The two observations of late season mating behaviors (blue lines) show that some of the adults experienced failure of their first attempt. This would also extend the total time period that terns use the colony area.

Secondary Goal 6: What disturbances were recorded, and how did the terns react to those disturbances?

Human disturbances

Skagway's Arctic Terns are very tolerant of frequent, predictable human disturbances. Vehicles that often and periodically traveled along the same pathway were essentially ignored. In fact, a few scrapes were located within inches of regular vehicle tire tracks. Vehicles that parked in the same parking areas over and over did not cause a reaction. Helicopter overflights and nearby landings did not seem to evoke any response within the colony. People driving or walking by on the access road or road shoulder did not provoke alarm within the colony.

Predators

The Skagway terns tolerate a very high level of human disturbance, at the same time they also expose themselves to potential damage from humans. Scrapes placed near vehicle tracks are in danger of physical destruction if the vehicle drivers deviate off-track at those locations. At any time, vehicles and/or people may impinge on sites that terns occupied because they seemed to be removed from such disturbances.

Two factors may explain why the terns find the colony area attractive despite these risks. First, the Ore Peninsula is very close to the mouth of the Skagway River, where abundant food can be obtained without expending much energy traveling to and from the feeding site. Second, the human disturbances may function to protect the nesting terns from land predators.

Some Skagway colony scrapes were placed as close as 1-2 yards apart. Many scrapes were about 5-10 yards apart. This spacing indicates low pressure from land predators such as fox, weasels, and river otters. Studies show without pressure from land predators, spacing between nests is usually about 1-9 yards apart; whereas with land predators it increases to about 55 yards apart. ^[1]

The colony was subject to avian predators, such as gulls, corvids and hawks. One observer reported seeing about 55 terns flush from the colony when a couple of gulls repeatedly swooped into the nesting area.

Internal disturbances

Late in the season, some Arctic Terns seem to act toward the last chicks in a hostile manner. Several observers noted adults and/or immature terns mobbing a parent trying to feed a late chick.

On a few occasions, one chick displayed a submissive, low posture in the presence of a non-nurturing adult; while soon afterward jumping up and calling to be fed in the presence of other adults. In a different incident, an adult was seen grabbing and violently throwing a chick to the ground.

These behaviors could indicate that at some point caring for late chicks may be detrimental at the colony level. This could lead to some adults acting to end care and/or some immature terns to compete for food intended for chicks.