During the 1981 breeding season, nesting of the Interior Least Tern (Sterna albifrons athalassos) and Belted Piping Plover (Charadrius melodus circumcintus) was noted at several locations on the Platte River in eastern Nebraska. The first location was a colony southeast of Shramm Park State Recreation Area (SRA), originally visited on 8 June. This was the only breeding activity noted on a reach of the river from the Interstate 80 bridge down-stream to the railroad trestle near South Bend. Twenty Terns and 6 Piping Plovers were observed on the first visit. They were nesting on a two to three hectare (ha) island north and slightly west of South Bend, in Cass County. Ten Terns nests with 1 to 3 eggs each and 2 Plover nests, each with 3 eggs, were located during a 30 minute visit. On 15 June a 1.25-hour visit was made to this colony. The period of visit included time spent observing behavioral activities from the periphery of the nesting area, thereby reducing disturbance to the breeding birds. Thirty Terns and 14 nests containing 1 to 3 eggs each were located. Two Plover nests, each with 4 eggs were also found. On 1 July about the same number of adult Terns were present and 14 nests with 1 to 4 eggs each and 3 young with adults near the nest were found. The Plover nests, each which still had 4 eggs, were also noted. Courtship activity among the Terns was still occurring on this visit. A 22 July visit recorded only about 15 adult Terns and 2 recently fledged young. Only a single nest with 2 eggs was found. Two groups, each consisting of three young Plovers, were near the nest with adult birds.
Based on the number of nests located, this colony appears to be thriving. A minimum of 30 breeding adults could be expected to have occurred, as nests found on each visit were not always the ones located on earlier visits. Three different Plover nests were located and 12 birds were counted in the area on the first visit. The three pairs nested on the same bar as the Terns.
Since this breeding area is located only 400 meters (m) south of Shramm SRA it is subject to several disturbance factors. Recreational use such as swimming and the building of campfires occurred on or near the sandbar. A large bonfire had been burned within several meters of Tern and Plover nests. People observing the fire would probably have disturbed the incubating birds, although the actual impact on the nesting birds is unknown.
Access to the river is from a gravel road running along the north bank of the river. Terns flying above arid around the colony can easily be observed from parking areas along the road. One factor which may inhibit sandbar access is the main river channel. Water may reach 1.5 m in depth during high flows. During other periods the depth was approximately 1 m. To the south of the colony is an area of lake-side cabins and a sand and gravel mining operation. Access from this direction is limited to business operations and cabin owners. A gate across the road further limits access. Thus, disturbance from the south would be limited and none was noted.
Some vegetative encroachment is occurring but it does not appear to be an immediate threat to the breeding birds.
A second area checked for Terns and Plovers was from the Nebraska Highway 92 bridge downstream to a point 6.4 km (kilometer) down the river. During a 6 June census, 2 small Tern colonies and 2 Plover nesting areas were located. The main nesting area was a sandbar on the downstream end of an island located near the southwest corner of Two Rivers SRA. A second site for nesting terns was 800 m down river. Piping Plovers exhibiting breeding behavior were observed on almost every suitable sandbar. Plovers nested at both locations where the Terns were nesting and in addition a single nest with eggs was found 3 km down the river from the second site. This later site was located in Sarpy County, while the other sites were in Douglas County. About 35 Plovers were noted in the area checked on 6 June.
The Two Rivers North colony had only 6 or 7 adult Terns on the first visit and only 2 nests with 1 or 3 eggs were located. Numerous Piping Plovers were noted, however, with more than 20 adult birds occurring on the 500 m x 150 m sandbar. The Plover nests were scattered around the central portion of the bar. Several incubating adults, five nests, and a group of 3 young out of the nest were noted. On a return visit, 6 July, only 3 adult Terns were observed. These birds gave no indication of nesting activity, as they were not seen incubating nor did they exhibit nest defense behavior when the area, including locations of previously observed nests, was searched. As expected, no nests were located; the Terns apparently deserted their nests. The sandbar area was subject to heavy recreational use from visitors to nearby Two Rivers SRA, including wading in the river, hiking on the sandbars and limited vehicular disturbance. Despite the heavy human use that was apparent, Piping Plovers successfully reared young. Three different groups of 2 or 3 young were noted with adults near the nest on 6 July.
Two Rivers South colony was visited only once, on 6 June. Five adult Terns were observed and 2 nests, each with 3 eggs were found. Six adult Plovers and 3 nests with 1, 2, or 3 eggs were also seen. This sandbar was subject to less disturbance by foot traffic but inner-tubing, canoeing, and air-boating was observed in the river channel. These disturbances had little impact on the nesting birds, as the activity was considerably removed from the area of the nests.
On 10 June an area from the Union Pacific Platte River trestle southwest of Valley to the Highway 92 bridge was checked. Five Least Terns were observed in this 7.5 km stretch of the river. They did not appear to be associated with any particular sandbar and no specific breeding behavior was noted. Only 3 Piping Plovers were observed. Two of these were a pair which exhibited nest defense behavior. An empty nest scrape appeared to have been disrupted, possibly a result of human activity on the bar associated with cabins on the east bank of the river.
The final area checked for breeding activity was 10.5 km of the river from the Highway 77 bridge south of Fremont to the Highway 64 bridge near Leshara. Only one colony, Dry Gulch, was located, slightly west and 2 miles north of Leshara, in Saunders county. Eighteen adult Terns were counted on 30 June, but only 2 nests with 2 or 3 eggs could be located. On 14 July, only the 2 nests found on the first visit were found again. The number of adult Terns had decreased to 12. Although the number of adults should indicate that more nesting activity would be occurring, this is not believed to be the case. The colony was located in an area of the river bed containing many sandbars, but only a limited number of the bars appeared to be suitable breeding habitat. Most of the sandbars were only slightly elevated from the water level of the river and would be subject to flooding with increased river stages. Another higher, dryer sandbar was covered to a large degree by vegetation, making it unsuitable for nesting Terns. The actual area of nesting was less than .25 ha. Since 2 nests were already present, additional nests would have to be placed in vegetated areas or on bars subject to inundation. It appears that the Terns are utilizing an area which historically could have been used but is now undergoing deterioration, resulting in decreased available habitat. In this area the wider, eastern channel was entirely without water and on 10 June it appeared to have been dry for several weeks, since vegetation was fairly well developed. The colony was located on a reach of the river where water again spread across the entire river channel. A reduction in flows in this reach meant the eastern channel was totally dry and was not suitable for nesting birds. This condition extended to about 1.6 km upriver from the colony site. Changes in flow regimes on the Platte have undoubtedly impacted the colony area, perhaps to a degree where the sandbar conditions required for nesting Terns and Plovers has been reduced in size and/or availability.
Additional nesting activity noted on this stretch of the river was a solitary nest situated near the Highway 64 bridge. a pair of Terns had a nest with 1 egg on 30 June. On 14 July the 2 Terns were still present but gave no indications they were still nesting. No nest could be found and the nest previously located was empty. The adult Terns were not observed in the area where the nest had been located but were foraging down river. Also on 14 July, 3 young Plovers were near the nest with adults at the Highway 64 bridge. These birds utilized a sandbar subject to human disturbance, as it was located beneath the bridge and was accessible from a mid-channel island.
Several similarities were noted at each of the Tern colonies. They were all located on river sandbars elevated 50 to 60 centimeters above the water level early in the breeding season, the beginning of June. Each sandbar was also subject to some degree of vegetative encroachment. Vegetative cover was estimated to be from 5 to 10%, with cottonwood (Populus deltoides) saplings the dominant plant. The amount of vegetative cover increased through the season as plants grew larger and as additional plants sprouted. On two occasions, Least Tern young were observed using the cover provided by vegetative growth. Each colony location was surrounded by river subchannels in addition to the main river channel. These subchannels were relatively shallow and from one to three would be present in the colony area. The Terns would feed in these nearby channels which provide forage fish such as minnows. Foraging Terns would also use subchannel areas up and down river from a colony. Observation of these birds away from the colony often indicates that a breeding site could be expected further along on the river.
Piping Plover habitat is very similar to that used by the Terns. The birds would nest in the snow area with nests rater-mixed in the available habitat. In one instance the RV() species nested with within one meter of one another. Aggressive encounters between nesting Plovers and Terns was noted on only one occasion. A Plover ran up to a Tern and pecked it when the Tern landed near its own nest to which it was returning. The Plover had recently fledged young within two to three meters of the nest. Nesting is so interspersed at times that if egg characteristics are not carefully' checked. the nesting species could be misidentified. In addition to the habitat used by both species, Plovers will utilize sandbars entirely free of vegetation and closer in elevation to the water level of the river.
Of the 65 Least Terns observed, only about half were known to be actively breeding. Shramm colony had the best reproductive success with almost all birds involved with nesting. Other sites were subject to human disturbance and habitat degradation which impacted the birds using the area. Piping Plovers were less subject to impacts and successfully raised a larger number of young at different locations.September 1981. Breeding of the least tern and piping plover on the lower Platte River, Nebraska. Nebraska Bird Review 49(3): 45-51.