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Long term reproduction data of Kentish Plover Charadrius alexandrinus along the Latium coast.

In this page we report some data on Kentish Plover along Latium’s coast for the period 1991-2009. An extended article will be published by Loris Pietrelli & Massimo Biondi in the Wader Study Group Bulletin.

The nest site preferences, breeding biology, population trend, details about the habitat usage and ecology of Kentish Plover Charadrius alexandrinus on sandy beaches of Latium (Central Italy) were studied since the 1990s. Kentish Plover breeds from the 2nd week of March to the end of June. Two temporal peaks of breeding activity were clearly distinguished before 2003.  A strong reduction of nesting pairs (-73.6%) was observed. High correlation between nest areas cover, distance from the sea and laying decades, have been found if large areas were excluded confirming different strategy between sites. The breeding biology (length of breeding season, egg volume, feeding time, distance from the sea) of Kentish Plover differs considering sites with reduced human activities. Correlation between nests cover, distance from the sea and laying decades within breeding season were observed. Actually the mechanical beach cleaning represents the main factor affecting the breeding biology of Kentish Plover.

Data were collected from 1991 to 2009 along the Latium coast (299 km long, including 236 km of sandy and 63 km of rocky beaches) . The solitary nesting and the use of temporary habitats shows the capability to survive of sub-optimal populations raising early clutches in small, increasingly isolated patches of habitat, but the strong reduction of breeding pairs (73.6%) due to loss of suitable sites (74.0%) and the reduction of available area observed during the 2009 breeding season strongly reduce the sustainability of Kentish Plover Latium population.

Kentish Plover, such as other ground-nesting birds, uses nest materials around their eggs because it both reduces the temperature fluctuation and provides camouflage for visually searching egg predator. A daily variations of nest materials were checked up in some cases, but the added nest material was mainly observed following a disturbance by human activities or by predators: probably the amount of material is related to the risk of nest predation. Similarly the significant changes, as breeding season proceeds, in the vegetation cover and in the distance from the sea observed following the clutch failure probably is the effect of a “strategic” withdraw to obtain positive nest fate. After clutch failure induced by human or natural causes other than predation, pairs tend to withdraw till dune. This hypothesis has been confirmed by the high relationship existing between the decade of deposition and the distance from the sea. This behavior is particularly evident for small nesting site (surface <15 ha): excluding Castelporziano Park, (6 km of protected and inaccessible beach), the correlation coefficient increase. Generally during the breeding season, at Castelporziano Park a horizontal (respect to the line-coast) movement of pairs and an increase of camouflage after clutch failure were observed (i.e. frequently nested under driftwood or other object scattered over the beach). In the smaller sites the distance between the first and replacement nesting attempts is much less than that found by Fraga & Amat (1996): the poor extension of sites coupled with the increasing human activities, allows “strategic” withdraw only. The initial response of individuals to human-induced change is often behavioral, anyway Kentish plovers laid the early clutches  in March-April when the beaches are responding to their requirements.

Pullus estimated age 8 days

Nest spacing (DNca) was similar within years with a nearest neighbor of 6 m  but the median yearly distances (>100 m) were high if compared with other similar size breeding populations. Others studies indicate that a wide dispersion of  nests may be the best strategy for birds unable to defend their nests against visually searching predators. In particular at a breeding size with few scattered pairs other defense methods are applied. This is particularly evident at Castelporziano Park where commonly high predation level was observed.

The laying calendar is comparable to other data found in literature for the Mediterranean areas, the Arabian Peninsula but about one month earlier if compared with the Atlantic area and Asia populations populations. The quantitative analysis of the entomofauna along the Tyrrhenian coast shows that the breeding season starts when the arthropod food resources reach their peak.

The interval for egg laying was similar to other Mediterranean sites but less than half time respecting the North of France while the period between the egg loss and the replacement seems to be the minimum required for egg formation.

The clutch distribution clearly shows two peaks where the second is due to replacement and second clutches. Counting the days between the first and last laying for each year a strong reduction of the reproduction season along the Latium coast was observed: the median number of days change from 89-103 days observed between 1991-98 to 64 days (-37.9%) recorded during the 2009 breeding season (the last laying occurred in May). Likewise in a Spanish area with low human disturbance clutches have been find within 100-105 days against 70-75 days where human pressure was higher while 88-110 days were registered for a Saline Lake population. The consequence is that at least the replacement clutches were detected but the second clutch, normally followed the hatching success, were not observed and, moreover, an alarming precocity of departures from the breeding site were observed starting from 2008.

The mean clutch size was similar to other Mediterranean areas. The hatching and fledging rate yearly decrease (about 50%) starting from 2007 but the ratio fledging/clutching can be considered constant: probably along the Latium coast, the incubation phase is much more affected than the young growing by the strong impact  caused by  human activities (i.e. daily mechanical beaches cleaning). Page et al (1983) assume that 0.80 young for breeding female were required annually for Kentish Plover population maintenance, moreover, according to Boyd (1962) a 5.2% decrease of colony size correspond to a female fertility of 0.71. Therefore, assuming these values as reference, we can observe that during the nineties years, females produced 22-23 fledging young corresponding to 0.64-0.78 young/female. These values are much close to the 0.8, minimum rate, required for population stability and this suggest that the second broods must be commonly produced to maintain this population: in Figure 1 it can be clearly observed the disappearance of the second brood starting from last years. Therefore, the 2009 production of 0.33 young per female is not likely sufficient to maintain a stable Latium population also considering both, the low juvenile survival after fledging and a mortality rate of 40-45% based on live recaptured of marked birds.

The nest fate such as the natural predation level does not shows change within decades, probably due to the small size and scattered populations level. The human disturbance on the contrary represents an important factor affecting the species survival probably due to the expenditure of time and energy to avoid humans: according to Burger (1993) when human disturbances increased, shorebirds spend less than 40% of their time to forage. Consequently, the hatching and fledging seem to depend strongly on the weather condition particularly during the spring week-ends when many people use to go to the beach: many clutches were “not found” after sunny weekends. It is known that a decrease of human activity, particularly during weekends supports an increasing in bird density (unpublished data by authors).

Rates of predation of nests were independent of clutch size and Crows seem to be the most common predator (46%). As Little Ringed Plover shows preference for fresh water, saline sites should be undisputed but, considering that often river mouths or retro-dunal ponds are present,  competition with Charadrius dubius seems to be a cause of a “sub-optimal” nest site selection, in particular within the boundaries of the smaller sites. A surprising annexing case of nest with mixed eggs (C. alexandrinus and C. dubius) was also found in 2007 at Torre Flavia (Rome).

Annexing by Kentish Plover of nest and egg of Little Ringed Plover

The breeding biology of Kentish Plover at Castelporziano Park differs from patterns reported from smaller sites. Most of the differences can be related to the high number of predators (Red fox, Vulpes vulpes, Crows, Corvus sp., Gulls, Larus sp., etc) to the absolute absence of the human activities and to the conflict with Charadrius dubius that occurs within the smaller sites. As human activities are completely absent (Castelporziano Park), the length of the breeding season is steadily more extensive (>90 days), nest site selection differs, eggs seems to be biggest respecting the other sites (author’s unpublished data) and individuals, far from the nest, devote nearly 75% of their time foraging and 25% of their time avoiding predators (samples of 26 hours of diurnal observation). The authors, moreover, on the contrary respecting to other Latium sites, during the permanence on the beach were often mobbed similarly to predators. An encouraging experience was done to prevent predation at Castelporziano Park installing wire mesh enclosures: an effective 68.8% of survival hatched eggs was obtained. During the last three years, the most important cause of nest loss for Kentish Plover along the Latium coast was the human activity and in particular the daily clean of beaches by ranking and sieving the sand often with heavy mechanical equipment.

Nato a Cesena (FC) il 08/01/1954