Spatio-temporal variation in nesting success of colonial waterbirds under the impact of a non-native invasive predator

Colonial breeding in birds provides protection from predators and may be particularly important when birds have to cope with an invasive predator. The probability of nest predation in a colony can vary depending on several factors, such as the nest’s location in the colony and the level of aggregation of nests. We studied the nesting success of colonial great crested grebes and monitored the occurrence of the non-native invasive American mink in the colony. From among 92 grebe nests, 54.3% were successful. The daily survival rate (DSR) of grebe nests was positively affected by the increasing distance between the nest and lake shoreline, and negatively affected by the increasing distance between the nest and the five nearest grebe nests. The probability of mink occurrence in the colony increased with consecutive days of the breeding season and decreased with increasing distance from the lake shoreline. The DSR of grebe nests decreased with the increasing probability of mink occurrence along the shoreline distance gradient and the day of the breeding season. The results of the study confirm the impact of the American mink on waterbirds during the breeding season but also indicate that large breeding colonies are partially safe from mink predation, and that nest accessibility and the dilution effect influence the probability of nest survival. Our data suggest that the limited access to safe breeding sites on large lakes that can supply adult grebes and their chicks with food may affect bird productivity and population numbers at the landscape level.

Factors determining presence of passerines breeding within White Stork Ciconia ciconia nests

Nests of White Stork Ciconia ciconia are commonly used by various passerines as nesting sites. In this study, we investigated factors determining presence and number of pairs of species breeding within White Stork nests in an extensive farmland in NE Poland. In 133 (57%) out of 233 White Stork nests, we found at least one breeding pair of passerine bird. These were from three species: House Sparrows Passer domesticus (68% of 133 nests with co-breeding), Tree Sparrows Passer montanus (65%), and Starlings Sturnus vulgaris (30%). The probability of breeding passerines within White Stork nests increased with increasing nest thickness, and was significantly higher in currently occupied nests. Sparrows were more likely to breed in White Stork nests located on electricity poles, situated closer to settlements and surrounded mainly by arable fields where meadows were not prevalent. In this paper, we show that White Stork nests are favorable nesting sites for passerines, as they are well insulated and provide an anti-predatory shield.

A few long versus many short foraging trips: different foraging strategies of lesser kestrel sexes during breeding

BACKGROUND

In species with biparental care both members of the breeding pair cooperate to raise the offspring either by assisting each other in every reproductive task or by specializing in different ones. The latter case is known as reproductive role specialization. Raptors are considered one of the most role-specialized groups, but little is known about parental behavior away from the nest. Until the advent of biologgers, avian role specialization was traditionally studied with direct observations at the nest because of the difficulties of following and recording the behavior of free-ranging individuals. In this paper we analyze how the role specialization of the lesser kestrel (Falco naumanni) influences foraging movement patterns throughout the breeding season. We tracked 30 lesser kestrel breeders from two breeding colonies using high-frequency GPS-dataloggers during four consecutive breeding seasons.

RESULTS

We found no differences between sexes in lesser kestrel foraging movements early in the breeding season before the formation of the breeding pair. However, we observed sexually distinct foraging movement strategies later in the breeding season once breeding pairs were formed. Lesser kestrel males performed a large number of short foraging trips while females made a few long ones. This maximized the provisioning rate by males to feed their mates and offspring. Meanwhile, lesser kestrel females spent more time at the colony than males in order to defend the nest, incubate the eggs and brood the nestlings. Females also helped their mates to provision the nestling once these had grown and required more food and less protection. Furthermore, lesser kestrels showed a sexual spatial segregation in foraging areas, with males foraging closer to the colony than females.

CONCLUSIONS

The lesser kestrel responds to changes in energy demand throughout the breeding season with its foraging movement strategy, but in a different way depending on parental sex. The sexual spatial segregation observed is likely to be the result of an adaptive foraging strategy based on role specialization to reduce prey depletion close to the colony and intersexual competition in order to improve breeding success.

Determinants of between-year burrow re-occupation in a colony of the European bee-eater Merops apiaster

Re-occupation of existing nesting burrows in the European bee-eater Merops apiaster has only rarely – and if so mostly anecdotically – been documented in the literature record, although such behavior would substantially save time and energy. In this study, we quantify burrow re-occupation in a German colony over a period of eleven years and identify ecological variables determining reuse probability. Of 179 recorded broods, 54% took place in a reused burrow and the overall probability that one of 75 individually recognized burrows would be reused in a given subsequent year was estimated as 26.4%. This indicates that between-year burrow reuse is a common behavior in the study colony which contrasts with findings from studies in other colonies. Furthermore, burrow re-occupation probability declined highly significantly with increasing age of the breeding wall. Statistical separation of within- and between-burrow effects of the age of the breeding wall revealed that a decline in re-occupation probability with individual burrow age was responsible for this and not a selective disappearance of burrows with high re-occupation probability over time. Limited duty cycles of individual burrows may be caused by accumulating detritus or decreasing stability with increasing burrow age. Alternatively, burrow fidelity may presuppose pair fidelity which may also explain the observed restricted burrow reuse duty cycles. A consequent next step would be to extend our within-colony approach to other colonies and compare the ecological circumstances under which bee-eaters reuse breeding burrows.

[Breeding ecology of Chinese Bulbul in the urban environment of Hangzhou, China]

The Chinese Bulbul, Pycnonotus sinensis, is one of the most abundant and widely distributed birds of south China, settling even in dense urban areas. From March-July 2012, we surveyed the Chinese Bulbul in the urban environment of Hangzhou, China, to gain a clearer perspective on their breeding ecology. Totally, 117 nests were found, mainly on the trees of Osmanthus fragrans (84.6%, n=117) in residential areas,street tree strips, and green belt. Our results include several noteworthy observations: nest height from the ground was 3.16±0.91 m (n=117); egg-laying begins in early April with peak times from April 11-25; and the nesting period was 11.85±1.12 days (n=47). In terms of fertility and reproduction, we also observed that the average incubation period was 11.34±1.12 days (n=32); average clutch size was 3.37±0.48 eggs (n=103); hatching success 68.3%, fledging rate 52.1%, and the total breeding success 35.58% (n=117). The main causes of breeding failure included egg and fledgling predation, as well as human disturbance.