23 January 2013

Tern and Plover Breeding on Lower Platte, 1982

During the 1982 breeding season, the Interior Least Tern (Sterna albifrons athalassos) and Belted Piping Plover (Charadrius melodus circumcintus) were once again found to be nesting along the lower Platte River in eastern Nebraska. Instead of the hiking involved while searching for colonies in 1981, efforts to locate nesting sites were easier this year because of an aerial survey of the river conducted by the Nebraska Game and Parks Commission. This census included the Platte from the Missouri west to the Big Bend area in central Nebraska. During this flight, locations where Tern activity was noted were marked on a county map. Those places where several Terns had been sighted were then visited to verify nesting status. Although a larger area was covered by the aerial census, this report is concerned only with the approximately 100 kilometer stretch of the Platte from the Missouri upstream to the western boundary of Dodge and Saunders counties (Figure 1). Six sites were visited twice to evaluate nesting activity and success. A few other locations where just 1-2 birds had been observed from the air were not checked.

Figure 1. Location of Interior Least Tern colonies on the lower Platte River, Nebraska.

The first area west of the Missouri River where Tern activity was noted was in Sarpy County just north of Cedar Creek in Cass county. Easily accessible, Cedar Creek Colony was first visited on 2 July. Eight adult Terns were counted with 3 nests containing 1 or 3 eggs scattered around the sandbar. About 8 Piping Plover were also present and although through a spotting scope an adult could be seen incubating, no nest could be found when the site was approached directly. During a second visit on 28 July, 11 Terns were observed. This included 8 adults and 3 fledged, flying young that were part of a family group of 5. One nest observed contained a single egg still being incubated by an adult. No Piping Plover were seen.

The sandbar that the Terns were using as a nest site was less than 200 meters (m) north of the housing area along the south bank that comprised the town of Cedar Creek. A gravel road that provides drive access to the cabins also provides easy access to the colony area. A river subchannel with a depth that varied from 1 to 1.5 m separates the sandbar from the south bank. Some recreational use of the nesting area was noted. The sandpit lakes which the housing was built around did provide a foraging spot for the Terns.

Schramm Colony was also visited on 2 July when 10 Least Tern and 2 Piping Plover were observed. Only 2 Tern nests with 2 or 3 eggs were found. On 28 July, only 1 Tern was observe. This bird was foraging along the river and was not associated with the sandbar where nesting had been located on the previous visit.

The river bar used this year was in the same location but was quite different from the sandbar used by Terns and Plovers in the 1981 breeding season (NBR 49(3):45-51). The action of high river flows in the spring had made the sandbar longer and reduced the amount of elevated area. A site suitable for nesting was still present but not to the extent of last year. Both nests found were built on a small elevated area of only a few square meters. Those birds that did attempt to breed were subjected to disturbance by recreation. Empty beer cans and bottles, a salad dressing bottle, and other discarded refuse were evident on the sandbar. Refuse and a partially burned tree snag were present on 28 July right near where nests had been found on the first visit.

So instead of thriving successful 1981 colony of 30 Least Tern and 12 Piping Plover, this year Schramm had fewer birds and they did not appear to have any nesting success. This was probably a result of less available habitat and disturbance of birds and nests that were present.

Two Rivers Colony did, however, have successful Tern nesting this year when compared to 1981 results. Piping Plover did not share in this success. On 1 July, 12 Terns were observed and 4 nests with I to 3 eggs were located on the same area of the sandbar that had been used last year. At least 4 Plover were present but no nests were located. Five Terns and no Plovers were present the second visit on 30 July. Although no young Terns were observed, aggressive defensive behavior and an adult carrying food would suggest that young were still present. Five additional adults and 2 fledged, flying young had been present on the previous day (John Dinan pers. comm.).

This season, less recreational activity was evident on the sandbar. A water depth of around 2 m in some spots meant swimming was necessary to reach the nest site in early July whereas later in the month it could be easily reached by wading.

One factor that could have contributed to the reduction in nesting Piping Plover was that the sandbar was not as large this year. Instead of the water flowing around the nesting area, a river subchannel had cut through the sandbar and reduced its size by at least half.

Access to this colony is through Two Rivers State Recreation Area and an adjacent state wildlife management area to the south. A portion of the nest sandbar is a part of the wildlife lands and since the Game Commission does own the property, it could easily be managed for the benefit of breeding Terns and Plovers. In the years that birds are present, it would be especially appropriate to limit access to the immediate vicinity of the colony. Nesting birds could have an undisturbed breeding cycle, which could improve nesting success. Conservation or birding groups could be encouraged to monitor the colony to limit detrimental activities and to aid in species management. Informative warning signs could also be used to reduce recreational disturbance.

Habitat conditions at Dry Gulch Colony showed an improvement this year. More sand area was available and higher water flows meant water was present in the east river channel instead of it being completely dry. Ten Terns with 5 nests containing 1 or 2 eggs were observed at this site on 1 July. Piping Plover were also present but there were no indications of nesting activity. During the second visit on 30 July, only 3 adult Terns were present. On this date, the nests were not present, no young were observed, and no defensive behavior was displayed by the Terns present. Plovers were foraging on the sandbars. Despite improved habitat conditions, this colony once again did not successfully raise young.

Those nests that had been present on the first visit were on the highest, dryest part of the sandbar, 60 centimeters above the water level of the river. This elevation placed the nests a good distance above river flows and would have reduced the chance of high water levels inundating the nests and disrupting the breeding cycle. The nests were grouped in a very compact, 50 m square area. Such concentrated nesting could easily be affected by intense predation or human disturbance. It is not known what actually did disrupt nesting at this colony.

Ames Pit Colony was located North of the river at a privately owned sand and gravel operation southeast of Ames, Dodge County. Eight Terns were present on 1 July and 3 nests with 2 or 3 eggs were found. On 30 July, 5 adult terns and 2 fledged, flying young were present. The nesting site was a sandy area that was a result of previous years' sand mining. This colony was not isolated by water and was easily accessible by road. Woody growth of willows and cottonwoods as well as remnant riparian woodland occurred on the west and south side of the colony. A lake to the east and the river to the south provided a place to forage for food. Sand removal equipment was in operation to the north. Conditions in the nearby Platte did not appear suitable for nesting birds. Only one small, low level sandbar was present adjacent to the colony area.

A final location where Least Tern were present was another private sand and gravel operation east of Morse Bluff, Saunders County. Rev. Thomas Hoffman of Omaha has been watching Terns and Plovers at this site for the past six years. Nesting birds have been present in recent breeding seasons and this year was no exception. Wolf Pit Colony had the greatest number of breeding birds of any area checked. On 1 July 30 Terns and 14 nests containing 1 to 3 eggs, eggs and young, or 1 to 3 young were found. Several young were mobile and had left the nest scrape but were nearby in the shade of plants. The actual number of Piping Plover present was not determined since they were scattered over a large area but 6 nests with 1 or 4 eggs were located. Only 1 nest contained a single egg.

Figure 2. Sand deposits used by Least Tern and Piping Plover at Wolf Pit Colony. Nests were found on the circular areas at the top of the photograph and the square area on the left. A recently created sand deposit is present on the right.

The Terns and Plovers were nesting on three separate but adjacent sand piles (Figure 2). Two were circular spill piles while the third was two smaller areas that when combined, created a fairly large sand expanse with a road through the middle. During the period of observation each group of Terns at a particular site would respond only to disturbance in the immediate vicinity. This was a help in getting a better visual estimate of the number of birds.

On 30 July, 10 adult Terns and 10 fledged, flying young were observed. Additional birds could have been present but the Terns were spread over a large area and their continual flying about made counting actual numbers difficult. Those counted were observed when they stopped flying and came to rest at two lakeside locations. These congregations on the sand beach were juvenile birds and their parents that would return from foraging to provide food. The young could fly but they were not seen to attempt catching food on their own. Other Terns had probably already left the colony area since sufficient time had elapsed for the fledged young present on the first visit to reach flight stage. No Tern or Plover nests were found during a brief search and an actual count of Piping Plover was not made.

This sand gravel operation, which has been present since 1927, (Jack Edwards pers. comm.), has over 25 circular or semi-circular sand deposits that are evident on recent Agricultural Stabilization and Conservation Service photographs of this section of land. Most of these deposits are a little less than 100 m in diameter, usually surrounded by water on three sides, and covered by a variety of willows, cottonwood samplings, different grasses, and other less prevalent species. The amount of plant cover varied on each deposit, with the older piles having a greater degree of plant growth. Some areas were nearly completely vegetated but some sand and the characteristic deposit shape were still evident on the aerial photo. A portion of the land with extensive woody vegetation had been developed for housing.

An important part of this colony site was that additional habitat was continually being provided as new sand areas were created by the sand dredging operations. Terns and Plovers through the years could have utilized the different spill piles for breeding activities. As older areas were overgrown by plants, the birds could move to nearby sand that was free of vegetation. Also of importance is that this nest base would provide protection from the higher water flows that flood nest sites in the river channel. Nesting that would get underway earlier in the season would not be disturbed and young could fledge earlier in the summer. However, since these nest sites are not isolated from land, they could be more susceptible to terrestrial predators. This could result in increased mortality of eggs and young.

The current owner of this sand pit showed an intense interest in the breeding Terns. Not only did he enjoy observing the birds but he worked at reducing chances of predation by selectively removing any bullsnakes that were observed near a colony. This interest also helped reduce human disturbance by limiting access during the breeding season. Activities associated with the transportation of sand seemed to have minimal effect, if any, on nesting birds. One Tern nest within 5 m of a road was kept under observation by Mr. Edwards. The incubating adult did not leave the scrape even as large trucks carrying sand would drive by. This nest eventually successfully fledged 3 young.

Overall, Wolf Pit was the most successful colony with a minimum of 10 fledged Terns. This was the highest number of fledged young observed during the late July visits to the colonies under observation (Table 1).

[Table 1. Least Tern survey results.]
Colony Name Cedar Creek Schramm Two Rivers Dry Gulch Ames Pit Wolf Pit Total
Aerial Count 28-29 June 10 3-4 0 12 4+ 15 45
Ground Count
1-2 July Individuals 8 10 12 10 8 30 78
  Nests Located 3 2 4 5 3 14 31
28-30 July Individuals 11 1 5 3 5 20 45
  Nests Located 1 0 0 0 0 0 1
Fledged Young Late July 3 0 2 0 2 10 17
Nesting Success (1) 1981 N.V. yes no no N.V. N.V.  
  1982 yes no yes no yes yes  

(1) Success is defined as the presence of flying young.

N.V. Not visited.

The 1982 breeding season for Least Tern showed an improvement over the results apparent in 1981. This survey did include a larger number of locations so data is not comparable. Those Terns present did however, successfully raise young at more of the nesting colonies checked (Table 1). This does not necessarily mean there was an improvement over last year but there was an increase in the known breeding success.

Those locations where a comparison is possible, show the change in populations that can occur from one year to the next (Table 2). Schramm Colony, as an example, which was the most successful nest site last year, had fewer birds and was a complete failure this season. Two Rivers was a success this year but a failure for Terns in 1981.

Table 2. A comparison of 1981 and 1982 populations of Least Tern and Piping Plover for selected lower Platte locations.
Colony Name Least Tern Piping Plover
  1981 1982 1981 1982
Schramm 30 10 12 2
Two Rivers 6-7 12 20 4
Dry Gulch 18 10 -- --

Available data for Piping Plover showed no increase in the number of breeding birds but a marked decrease in the number of nesting attempts. Even though a larger number of colony locations were checked, populations at these sites were somewhat similar for both years. Schramm and Two Rivers had good numbers of nesting Plovers last year but no indications of breeding activity this year. Wolf Pit was the only exception with the number of nests found indicating a healthy breeding population. A single adult observed incubating at Cedar Creek was the only other activity noted for the six locations that were visited. Nesting was limited this year and the increase in breeding birds that would be expected as additional sites were checked just did not occur. Successful nesting observed at only one of six locations meant a dismal breeding season for Piping Plover.

September 1982. The 1982 least tern and piping plover breeding season on the lower Platte River, Nebraska. Nebraska Bird Review 50(3): 68-72.

Father Hoffman sent in this observation about the Piping Plovers at Morse Bluff: On 25 June and on 6 July I observed pairs of adult Piping Plovers with downy young (three in each case). The time lapse and the fact that the two observations were a considerable distance apart and separated by roads, weedy fields, and woodlands indicate to me two different broods. In both cases the birds were on tailings from sand-pit operations. [Editor]