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Studies of vigilant behavior in an urban flock of Swan Geese (Anser cygnoides) and their hybrids in Heidelberg in southwest Germany were carried out between 31 May and 22 July 2002. The habitat is characterized by a high rate of human disturbance and by artificial feeding. The following hypotheses were tested: (i) vigilance is increased due to disturbances on many occasions, (ii) vigilance should follow general patterns found in natural populations, e.g., the many-eyes hypothesis and (iii) vigilance may or may not differ between hybrids and true Swan Geese. Time spent vigilant during a 2-minute-bout of grazing averaged 15.5 s, which made up 13% of the time budget. This amount is not high compared to studies of other geese species in natural environments. There was no difference between Swan Geese and their hybrids in the duration. Vigilance was not dependent upon the number of birds present as predicted by the many-eyes hypothesis, and did not depend on the distance to water line nor position of the bird (center versus edge of the flock). Therefore, vigilance may serve other functions such as stealing food from others, detecting human passers-by with food or avoid interference between conspecifics.
Unlike other alcids, laying of replacement eggs has not been well documented in Brachyramphus murrelets. Observations of two radio-marked Marbled Murrelets (Brachyramphus marmoratus) in northern California during 2001 and 2002 suggested that they can re-lay in the same breeding season. In 2001, aircraft telemetry first detected a male Marbled Murrelet at a forested inland location on 17 May. This bird alternated 24h incubation bouts with 24h at sea periods until 29 May, when data logger recordings indicated that the bird arrived at the nest at 05.17 h (PDT), but left at 05.32 h. This nesting effort had apparently failed. Sixteen days later, on 14 June this murrelet arrived in the vicinity of the first nest site at 05.19 h and remained there until 18.57 h that same evening and then left. We suspected that this event represented a second breeding effort that also failed, either near or at the site of the first effort. In 2002 a female Marbled Murrelet, first detected inland on 13 June by aircraft telemetry, alternated on the nest one day and at sea the next until 23 June when the breeding effort is presumed to have failed. This bird was again detected inland on 21 July, and alternated on the nest one day and at sea the following day until 3 August, when the radio-transmitter fell off the bird. Video recordings at the nest site indicated this second nesting attempt continued until 1 September, when the chick died of unknown causes. As in other alcids, re-laying apparently occurred 2-4 weeks after failure of the first eggs, either near or at the site of first eggs. Re-nesting may be frequent in murrelets, given the high rates of breeding failure reported.
We surveyed Marbled Murrelets (Brachyramphus marmoratus) daily from small boats in Auke Bay and Fritz Cove, Alaska, from May through August 1992 and 1993. Differences in numbers of juveniles and in the timing of their presence in the study area between the two years indicated that breeding phenology was late and productivity was low in 1992 compared to 1993. This difference was consistent with variability in the physical environment. Of 99 fish identified in the bills of fish-holding adult murrelets, 81 (82%) were Pacific Sand Lance (Ammodytes hexapterus). Counts of fish-holding adult murrelets were significantly higher in the evening than at any other time of day. Time of day had no significant effects on counts of fledglings, indicating that juveniles were moving into and out of the study area during the day. Murrelets were predominantly found in groups of two or more, even during incubation, suggesting that murrelets incur an appreciable benefit, such as increased foraging efficiency, from foraging in groups. For both summers, there was no correlation between counts of murrelets on the water and numbers of murrelet detections in the adjacent forest. We suggest that many behavior patterns of the Marbled Murrelet (displaying, choosing of mates, and pair-bonding, finding of nest sites and successful foraging of juveniles) may be socially facilitated.
Eared Grebes (Podiceps nigricollis) encounter a variety of climatic regimes in their annual cycle. The most dramatic occur while on staging areas in autumn. We investigated the thermoregulatory abilities of the Eared Grebe to determine how they coped with these climate changes during staging. The basal metabolic rate (BMR) was higher than predicted. Mass-specific BMR was 1.212 mL O2/g·h for birds averaging 317 g. The thermoneutral zone is wide and extended from 15°C to 38°C. Minimal thermal conductance and average body temperature were not unusual. We conclude that Eared Grebes live most of the year under thermoneutral conditions and that food availability, not temperature extremes, determines the timing of their winter migration.
Avoidance of predators has long been regarded as a major benefit in colonial breeding. Nevertheless, field and comparative studies have not shown a clear relationship between predation and coloniality. In the present study, we examine the association between aerial egg predation on the Common Tern (Sterna hirundo), and sub-colony size, nest aggregation and reproductive synchrony. Fieldwork was carried out at the Ebro Delta colony (north-western Mediterranean), where Common Terns breed syntopically with potential predators. Sub-colonies placed in a small area were used instead of distant colonies in an attempt to minimize site effects, e.g., the abundance of predators. We used logistic regression with random effect (i.e., sub-colony) to test simultaneously the effect of the studied factors on the risk of predation. In addition, the random effect allowed us to account for the extra-binomial variability due to the potential non-independence of nests of the same sub-colony (clustered observations). Our results support the contention that both breeding in large colonies and in aggregated territories confers protection against aerial predators. In addition, synchrony in relation to the whole colony had no effect on the risk of egg predation. However, birds breeding asynchronously earlier in the season than the average in their own sub-colony were more likely to suffer egg predation than eggs from late asynchronous nesters.
The need to understand how wildlife responds to the broad-ranging impacts of development is becoming increasingly important as human populations around the globe continue to increase and urbanize. We studied waterbird behavioral associations with developed and undeveloped shorelines on four partially developed urban lakes in central Florida. Summer observations revealed that wading birds foraged significantly more along developed shoreline, and that ducks rested and tended young significantly more along developed shoreline. Winter observations revealed that marsh birds foraged significantly more along undeveloped shoreline but displayed active/swimming behavior significantly more along developed shoreline. Summer ducks and winter wading birds showed significantly greater alert/flee behavior along undeveloped shoreline. Ducks in both seasons showed significantly greater alert/flee behavior than other guilds. For all guilds, alert/flee behavior was seen 1.6 times more often in the winter. Winter migrants did not show greater alert/flee behavior than resident birds. Results show that a wide range of waterbirds can use urban lakes during the breeding and non-breeding seasons, and that many birds appear to favor developed shorelines for a variety of behavioral patterns. However, dense stands of tall emergent vegetation along undeveloped shoreline may limit waterbird behavior along this shoreline. The heightened alert/flee behavior observed along undeveloped shorelines may warrant the use of buffer zones to protect birds using these shorelines from undue human disturbance.
A comprehensive wading bird nesting database for the Everglades watershed in south Florida was compiled for the time period of 1903 through 2001. The limitations and applications of this database were assessed with the purpose of ultimately strengthening wading bird performance measures used as an index of ecosystem integrity for the Everglades restoration effort. The database is limited for some inferences, such as comparing between individual years, because of a lack of standardization in sampling methodology. As such, it should be used as an index of wading bird numbers rather than as an absolute population measure. However, the database is adequate to understand long-term, system-wide trends and the range of variability in nesting effort by the wading birds. Results from the analyses indicate that trends in numbers of nesting wading birds differ among species. It is estimated that the number of White Ibis (Eudocimus albus) and Wood Stork (Mycteria americana) nests have decreased by 87% and 78%, respectively, in the Everglades since the 1930s. There has also been a significant increase in the time interval between large nesting events for White Ibis and Wood Stork and a decrease in the magnitude of large nesting events for White Ibis over the past 70 years. The number of Great Egret (Ardea alba) nests has increased, the magnitude of large nesting events has increased, and the interval between large nesting events has decreased. There has also been a 61% decrease in the percentage of wading bird nests located in the southern Everglades and a 46% increase in the percentage of nests located in the central northern Everglades since the 1980s. These types of quantitative comparisons can be used to refine and strengthen the proposed wading bird performance measures used to gauge the health of the Everglades for the Everglades restoration effort. The time interval between large nesting events may be appropriate as an additional performance measure because it may capture the variable nature of wading bird numbers in response to hydrologic fluctuations in the Everglades.
Attempts at intraspecific kleptoparasitism by Lesser Black-backed Gulls (Larus fuscus) feeding at a rubbish dump in southwest Spain during the winter 2001-2002 were studied to measure differences in the frequency of attacks between the age classes, the success of the attacks and the existence of possible density-dependent kleptoparasitism. Significant age differences in the frequency of attacks initiated were not found, although first year birds received a higher number of attacks. The success of the attacks increased with the age of the kleptoparasite and decreased with the age of the victim. The gulls selected victims of an equal or younger age to their own. A correlation was found between density and number of attacks on most dates. The possibility exists that kleptoparasitism could influence the success of the recent expansion of the species in the Iberian Peninsula.
Many birds feed on bivalve molluscs, but only oystercatchers (Haematopus spp.) are known to prise open the shells. Brown Teal (Anas chlorotis), a dabbling duck endemic to New Zealand, were observed opening Common Cockles (Austrovenus stutchburyi) on Great Barrier Island. The teal jackhammered into the open shells of feeding cockles and quickly scooped out the flesh. Despite having the bill morphology of a typical dabbling duck, they were adept at this feeding method.
The effect of distance between members of pairs of the Ruddy Shelduck (Tadorna ferruginea) during vigilance behavior was studied during winter at Lijiang Lashihai Lake Reserve, southwest China. The distance between the paired birds while feeding was grouped into three categories: <1 m, 1-3 m and >3 m. Nearly 90% of the distances recorded between paired males and females were within three meters. The degree of vigilance increased with distance apart for females, but not for males. The scanning rate of males was significantly higher than that of females at <1 m and at 1-3 m respectively, but no significant difference occurred when the distance between them was >3 m. These results are discussed in relation to mate competition and wintering strategy; it is suggested that staying close together is the optimal strategy for members of Ruddy Shelduck pairs.
Recent taxonomic revisions of the Wandering Albatross sensu lato has resulted in four separate species, the rarest of which is the Tristan Albatross (Diomedea dabbenena). We present the first detailed morphometric measurements of the male and female of the Tristan Albatross. The results are used to separate this species from the more common nominate taxon of Wandering Albatross (Diomedea exulans) from South Georgia. The Tristan Albatross is smaller than the Wandering Albatross in all measured variables, and males are larger than females in both species. A combination of bill measurements discriminated 97-98% of individuals of the two species, and tarsus and bill measurements allowed the sex of birds from both species to be determined. If the sex of the bird is known, then bill length should identify all individuals to species. This result is useful to allow fishery observers to correctly identify albatrosses killed on longlines in the Atlantic Ocean. However, care has to be taken outside this region, because the Tristan Albatross is very similar in size to published measurements of Gibson’s Albatross (Diomedea gibsoni) and the Antipodes Albatross (Diomedea antipodensis), both of which breed off New Zealand and are thought to range across the South Pacific Ocean.
From 1995 through 1999, 2,240 individuals of 28 species of waterbirds were examined in the United States for ingested lead fishing weights. A combination of radiography and visual examination of stomachs was used to search for lead weights and blood and liver samples from live birds and carcasses, respectively, were collected for lead analysis. Ingested lead weights were found most frequently in the Common Loon (Gavia immer) (11 of 313 = 3.5%) and Brown Pelican (Pelecanus occidentalis) (10 of 365 = 2.7%), but also in one of 81 (1.2%) Double-crested Cormorants (Phalacrocorax auritus) and one of 11 (9.1%) Black-crowned Night Herons (Nycticorax nycticorax). Birds with ingested lead fishing weights (including split shot, jig heads, and egg, bell, and pyramid sinkers) were found in California, Florida, Maine, New Hampshire, North Carolina, and Wisconsin. The size and mass of ingested lead weights ranged from split shot of 7 mm in the longest dimension, weighing less than 2 g, to a 22 × 39 mm pyramid sinker that weighed 78.2 g. Six ingested lead weights were more than 25.4 mm in the longest dimension. Lead concentrations in the blood and liver of birds with lead fishing weights in their stomachs ranged up to 13.9 ppm and 26.0 ppm (wet weight basis), respectively. During the study, we also noted the presence of ingested or entangled fishing tackle, with no associated lead weights, in eight species.
Within the Murray-Darling Basin of eastern Australia there has been a general decline in the abundance of wading birds. Loss of wetlands caused by river regulation and irrigated agriculture is considered to be the main cause. We assessed the adequacy of irrigated rice fields as substitutes for natural wetlands for foraging egrets during the breeding season in one study area around a mixed colony of egrets in southeast Australia. For aerially sown rice crops, which represented 85% of all rice in the general area, the densities of foraging Intermediate Egret (Egretta intermedia) and Great Egret (Ardea alba) tended to reach a maximum four to six weeks after sowing of the rice crop, and declined thereafter. The decline phase was correlated with decreasing prey capture rates and a shift from vertebrate prey to less profitable invertebrate prey, and coincided with the start of the egrets’ main chick rearing period when food demands would have been high. Even at maximum densities it was estimated that only 5-13% of the Intermediate Egrets and Great Egrets that were available to feed actually did so in the rice growing areas within 6.5 km of the colony. In contrast, Cattle Egret (Bubulcus ibis) densities in rice fields did not decline until after their young fledged. They fed almost exclusively on insects and their prey capture rates showed no seasonal decrease. Up to 60% of the available Cattle Egrets were found feeding in the rice fields within 6.5 km of the colony. It is concluded that rice fields provide a good foraging habitat for the Cattle Egret and may be contributing to the spread of this invasive species, but that they are probably not a preferred foraging habitat for the Intermediate Egret and the Great Egret.
According to habitat selection theory, individuals selecting among habitat patches should either avoid or be attracted to conspecifics. This study examined Cattle Egrets (Bubulcus ibis) foraging around two grazing horses (Equus caballus), which represented two distinct habitat patches. The numbers of Cattle Egrets in the two patches were not significantly different, and the egrets were regularly distributed between the two patches. When settling in the two patches, 66% of the egrets selected the patch occupied by fewer conspecifics. All egrets choosing the patch occupied by more conspecifics did so only when the numbers of egrets in the two patches differed by one egret. When the numbers of egrets in the two patches differed by two or more egrets, newly arriving birds always chose the patch occupied by fewer conspecifics. As the number of egrets within a patch increased, nearest-neighbor distances decreased, and rates of aggression increased. Thus, these results indicate that the Cattle Egrets avoided conspecifics when selecting among habitat patches and that this distribution was achieved through individual patch selection decisions and density-dependent aggression.
We report on the food of breeding Great White Egrets (Ardea alba) in an agricultural ecosystem in southern Chile, South America. Analysis of diet was based on prey remains and pellets collected under the nesting trees during the reproductive season. Pellets indicated that insects were the most numerous prey items (78%), followed by the Southern Crayfish (Samastacus spinifrons) (21%). The Southern Crayfish accounted for 92% of the biomass. In terms of prey remains, the Southern Crayfish was the primary prey item accounting for 97% in frequency and 98% of the biomass. When pellets and prey remains were combined, the Southern Crayfish remained the most numerous prey item (67%), followed by insects (32%). The other prey items constituted less than 1%. Significant differences were found between the diets estimated by the two methods. We suggest that results of pellets and prey remains should be combined to evaluate the diet of the Great White Egret. Significantly, more crustaceans and fewer insects were consumed during the late part compared with the early part of the breeding period, and differences were found amongst the orders of insects taken in the same periods. The food of the Great White Egrets is influenced both by spatial availability patterns and profitability of prey type.
We examined the stomach contents of 64 male and 43 female Common Murres (Uria aalge) caught in gillnets during late chick rearing/early chick departure period in August 2002 near breeding colonies in Witless Bay, Newfoundland, Canada. Twenty-six percent of stomachs contained no food. All others contained exclusively fish, and Capelin (Mallotus villosus) was the only fish positively identified. Gravid female Capelin were found in 82% of murre stomachs with contents. The number of fish ingested by murres differed between the sexes, with a mean of 2.7 fish in male stomachs and 1.6 fish in female stomachs. Mean mass of stomach contents did not differ between the sexes (males: 27.0 g; females: 22.6 g). Overall, results were similar to Common Murre diets recorded in the 1980s, despite changes in Capelin distribution and biology. The sample of Common Murres collected as gillnet bycatch was male-biased (59%). Males may have been more vulnerable to being caught in gillnets, perhaps because they were engaged in different activities at this late stage of chick rearing.
Winter breeding by Black-crowned Night Heron (Nycticorax nycticorax) in l’Albufera de Valencia, Spain, during three consecutive years is described. Winter presence in the area was recorded since 1995 and winter breeding was first confirmed in February 2001. Nests were built at roosts in wooded areas on a barrier beach, using tall pine trees (Pinus halepensis). The number of birds attending the roosts ranged 100-200 individuals, but only nine to eleven nests were built each year and only a few chicks survived to fledging. We suggest that the abundance of the introduced Red Swamp Crayfish (Procambarus clarkii) increased food availability when rice field were ploughed in early winter, and mild temperatures may have encouraged Black-crowned Night Herons to extend their presence into the winter season and to permit egg laying into the winter months. Nevertheless, the extra food supplied during rice field operations declined markedly in March and may have forced nest desertions that month.