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On the function of territory in gulls
Abstract
Bearing in mind that, in the absence of experimental proof of the functions suggested, my conclusions are tentative, I have tabulated them as follows. The relative importance of each function is expressed in a crude classification, ranging from O=no function to 3=important function.
... Because body size is related with an individual's competitive ability (Johnsson et al. 1999;Serrano-Meneses et al. 2007), and since most seabirds are sexually dimorphic, agonistic interactions are predominantly performed by the larger sex, often males. Individuals of the larger sex play a major role in acquiring and defending nesting sites (Tinbergen 1956;Butler and Janes-Butler 1983;Paredes and Insley 2010). In Northern gannets, the larger males sometimes invest so much in territorial defence that they even lose more body weight than females do during egg laying (Montevecchi and Porter 1980). ...
... Competing for a new nesting site might be impossible because of time constraints or become very costly, and it could go along with the loss of the breeding partner (Cézilly et al. 2000). The high time investment of males during the early phase of the pre-laying period is likely relevant for territorial establishment (Tinbergen 1956;Butler and Janes-Butler 1983;Paredes and Insley 2010). Gulls show high levels of aggression during territorial defence, where larger sized males are likely in advantage. ...
... Gulls show high levels of aggression during territorial defence, where larger sized males are likely in advantage. Indeed, males are more involved in agonistic interactions, while females typically contribute passively by their presence in the territory (Tinbergen 1956;Pierotti 1981;Burger 1984). Agonistic interactions between individuals (i.e., behavioural investment), which is in turn related to the energetic costs of defending a territory, could not be quantified in this study. ...
Colonial breeding provides benefits such as reduced predation risk, but also entails costs due to the enhanced levels of competition. In particular, it may require a significant amount of time and energy to establish a territory at the onset of reproduction, which in turn can impose carry-over effects on subsequent reproductive investments. Here we made use of GPS tracking devices to test how a colonial breeder, the lesser black-backed gull (Larus fuscus), balances its time investment between territorial and foraging activities throughout the pre-laying period, and investigated possible fitness consequences. As hypothesized, individuals that spent more time in their territories reduced their foraging time, foraged closer to the colony, and spent less time commuting during foraging trips. Although males initially invested more time in establishing a territory, both sexes gradually spent more time in their territory as the onset of egg laying, an energetically demanding period, approached. Furthermore, males that exhibited a higher territory attendance alleviated the females’ time constraints for foraging and their partners laid larger eggs. Our results highlight the importance of quantifying carry-over effects related to time budgets during the (often understudied) pre-laying period, to better comprehend fitness consequences of colonial breeding.
... For the Slender-billed Gull (Larus genei), Common Tern (Sterna hi-rundo), and Gull-billed Tern (GeJocheJidon nilotica), pairs were organized before the flight of birds to the colony ,area (Isenmann, 1976;Cramp, 1985). In many species, pair formation takes place in "clubs," which are aggregations of prebreeding individuals, but adults from the colony as well as immature and prebreeding birds often loaf there (cf.Tinbergen, 1956;Nelson, 1984). Pair bonds are initiated in clubs for most seabirds, but they do not appear to be permanent in pelecaniform and some procellariform birds (Nelson, 1984). ...
... In the Western Gull (Larus occidentalis), the chief site of prebreed-ing aggregations and club territories is located immediately adjacent to the colony (Ewald et al., 1980). Females of the Laughing Gull temporarily abandon colonies and form "pair territories" in regions where there are small encroachments of settling gulls (Tinbergen, 1956;Burger and Beer, 1975). Black-headed Gulls in the stable colonies on Lake Kiyovo mainly form clubs on the site of the future colony (Kharitonov and Zubakin, 1984). ...
Colonial nesting in seabirds and other water birds is widespread, but it is relatively rare in other birds (Lack, 1966). A colony is a breeding aggregation of birds characterized by many individuals nesting close to each other, generally feeding outside the nesting area, and organized by various types of social stimulation and elements of flock behavior and other features (Crook, 1965; Modestov, 1967; Zubakin et ai., 1983; Götmark and Andersson, 1984). Colonies may have an internal structure in which there are elements of territoriality and social synchrony (Naumov, 1972). The processes of how colonies form and function have been investigated emphasizing two distinct points of view. The first is the phylogeny of coloniality—the formation of colonies in context of evolutionary processes; the second is the ontogeny of coloniality—the formation of colonies during the season of reproduction.
... The following patterns emerge. (i) Incubation and brooding are usually performed more by females than by males (gulls: Pierotti 1981; Butler and Janes-Butler 1983; Hand 1986; terns: Wiggins and Morris 1987; Wagner and Safina 1989; Quinn 1990; for Little and Common terns: this study), but there are cases of equal sharing, in both gulls (Tinbergen 1956; Morris and Bidochka 1982; Morris 1987; Henzi et al. 1990) and terns (Uttley 1992; this study (Sandwich Tern)). (ii) Territory attendance and defence by means of agonistic interactions are mainly male duties in gulls (Tinbergen 1956; Southern 1981; Pierotti 1981 ; Morris and Bidochka 1982; Butler and ...
... (i) Incubation and brooding are usually performed more by females than by males (gulls: Pierotti 1981; Butler and Janes-Butler 1983; Hand 1986; terns: Wiggins and Morris 1987; Wagner and Safina 1989; Quinn 1990; for Little and Common terns: this study), but there are cases of equal sharing, in both gulls (Tinbergen 1956; Morris and Bidochka 1982; Morris 1987; Henzi et al. 1990) and terns (Uttley 1992; this study (Sandwich Tern)). (ii) Territory attendance and defence by means of agonistic interactions are mainly male duties in gulls (Tinbergen 1956; Southern 1981; Pierotti 1981 ; Morris and Bidochka 1982; Butler and ...
We studied parental-care allocation by males and females in three tern species. Female Common Terns (Sterna hirundo) and Little Terns (S. albifrons) performed more incubation and brooding than males, whereas in the Sandwich Tern (S. sandvicensis) the sexes shared these duties equally. In all three species, agonistic behaviors were performed equally by females and males. Prey types brought by males and females of each species were similar, but males tended to bring larger prey and had higher delivery rates than females. Information on parental-care allocation by female and male seabirds of various species, 5 gulls, 6 terns, and 1 skimmer, indicates that females perform most of the incubation and brooding in both gulls and terns, whereas males perform most territory attendance and agonistic behavior (gulls) and more prey provisioning (terns). These patterns are qualitatively consistent with the explanation that the differences between gulls and terns in sex-biased parental care are related to the fact that gulls exhibit sexual size dimorphism but terns do not. Contrary to theoretical predictions that in monogamous birds, females contribute more reproductive effort than males, in all the seabird species studied so far the total parental expenditure by males seems to equal or outweigh that by females.
... Considering the above arguments, it seems more plausible that a preference to economize on energy drives to a greater specialization of females in terrestrial foraging. As mentioned before, marine foraging allows for a greater time-efficiency, so that males may spend a longer time at the colony, enhancing brood or territory defense, for which they might be more impelled to than females (Alonso-Alvarez 2001;Tinbergen 1956). These interpretations therefore point in the direction of sexual differences in optimization criteria, where females prioritize energy-efficiency and males prioritize time-efficiency. ...
... Tinbergen recorded the analogous phenomenon in disturbed or heavily predated colonies of Herring Gulls (Larus argentatus). The gulls abandoned their nests in the central parts of the colony and moved to the periphery thus spacing out and forming less dense settlements (Tinbergen, 1956). ...
The phenomenon of nest relocation was found in colonies of Gull-billed Terns on Lakes Shalkar and Ayke, southern Russia, in 2000 and 2001. The phenomenon manifested itself largely on Lake Shalkar in 2001, while research work was conducted in a Gull-billed Tern colony. After visiting the island that colony occupied, during 14 days it was observed that some birds had abandoned their nests mainly in the densest plots of the colony, and at the same time new nests had appeared on the colony periphery. A typical detached nesting site of the colony (the sample plot) was charted on the map. In the sample plot, the number of nests decreased 1.7 times – from 113, before research work, to 68, after work in the colony. The sample plot area increased from 130.8 m2 to 161.3 m2, the length increased from 19.0 m to 21.1 m. Mean nearest-neighbor distance increased from 70.6 ± 2.2 cm (n = 113) to 96.4 ± 4.9 cm (n = 68; t180 = 5.5; p < 0.0001), density reduced 2.1 times – from 0.9 to 0.4 nests per m2. It is supposed that such changes in the colony territorial structure resulted from repeated human disturbance caused by the long-term research activity in this colony of Gull-billed Terns. ***
Barbazyuk, E.V. Responses to human disturbance from nesting Gull-billed Terns // Беркут (Golden Eagle). 2005. V. 14, Issue 2. P. 221–230.
... Àíàëèç ëèòåðàòóðû ïîêàçûâàåò, ÷òî ïîëîaeåíèå ãíåçäà â êîëîíèè îïðåäåëÿåòñÿ: 1) ñòðåìëåíèåì ê ñîâìåñòíîìó ãíåçäîâàíèþ, ÷òî âûðàaeàåòñÿ â îáðàçîâàíèè íåáîëüøèõ ãðóïï ãíåçä è ñîáñòâåííî êîëîíèè (Çóáàêèí, 1983; Ïàíîâ, 1983à, 1983á; Ïëþñíèí, 1983); 2) òåððèòîðèàëüíûì àíòàãîíèçìîì ñòðåìëåíèåì êàaeäîé ïàðû ñîõðàíÿòü âîêðóã ñåáÿ îïðåäåëåííóþ òåððèòîðèþ (Òèíáåðãåí, 1974; Ïëþñíèí, 1983; Kharitonov, Siegel-Causey, 1988; Kharitonov, 1998); 3) íåîäíîðîäíîñòüþ ìåñòîîáèòàíèÿ, â êîòîðîì âñòðå÷àþòñÿ ó÷àñòêè, îáëàäàþùèå ðàçëè÷íîé ïðèâëåêàòåëüíîñòüþ äëÿ ïòèö, è îáëàñòè, âîîáùå íåïðèãîäíûå äëÿ óñòðîéñòâà ãíåçä ( Kharitonov, 1998). Ó êîëîíèàëüíûõ âèäîâ ðàçëè÷àþò ñëåäóþùèå îáëàñòè âîêðóã ãíåçäà: 1) ñîáñòâåííî òåððèòîðèÿ îõðàíÿåìàÿ îáëàñòü âîêðóã ãíåçäà èëè ìåñòà, ãäå îíî áóäåò ïîñòðîåíî (Tinbergen, 1956 ); 2) äîìàøíåå ïðîñòðàíñòâî (home range) îáëàñòü âîêðóã ãíåçäà, ãäå ïòèöà ìîaeåò ïåðåäâèãàòüñÿ (Odum, Kuenzber, 1955); 3) ñåðäöåâèííàÿ çîíà (core area) îáëàñòü âîêðóã ãíåçäà, â êîòîðóþ íå äîïóñêàþòñÿ ïîñòîðîííèå îñîáè , çà èñêëþ÷åíèåì äîìèíàíòíûõ (ñì. âûøå ), íàëè÷èå è ðàçìåðû êîòîðîé ìîãóò áûòü óñòàíîâëåíû òîëüêî ñ ïîìîùüþ ñïåöèàëüíûõ ýêñïåðèìåíòîâ ñ ïåðåìåùåíèåì ãíåçä (Kharitonov, 1998 ). ...
... Despite considerable re- search, the structure and functions of bird ter- ritory as a dispersal mechanism remain insuf- ficiently studied. The territorial factor in co- lonial waterbirds is not by itself a sufficient condition for regulation of population density through territorial behavior, because the size of a territory may vary greatly even in the course of one reproductive season for ex- ample, it may decrease under pressure from new intruders settling among existing nests in a colony (Tinbergen, 1956;Kharitonov, 1998;Panov, Zykova, 2002), which appears to sup- press its regulatory function. To understand how the factor of territory prevents over- crowding, it is necessary to take a closer look at what the territory is, i.e., examine in detail its internal structure. ...
The nest territory structure and territorial behavior of the Gull-billed Tern was studied at Lakes Shalkar and Ayke (southern Russia) in 2000, 2001 and 2003. To examine the defended area around nests, field experiments were conducted during which one nest was moved gradually toward the nearest neighboring nest. The area surrounding a Gull-billed Tern nest was shown to consist of at least three territorial units, not visible by direct observation: immediately surrounding the nest is a small area designated as the Core Area; the Core Area is surrounded by a larger area called the Conflict Zone, consisting of a more aggressive Inner Layer directly bor-dering the Core Zone, and a less aggressive Outer Layer. The hostility of the both birds increased as the distance between the nests lessened. In the Core Area tern aggression was maximal, and was expressed by absolute in-tolerance of other individuals. Ýêñïåðèìåíòàëüíîå èçó÷åíèå ñòðóêòóðû òåððèòîðèè ó ÷àéêîíîñîé êðà÷êè. -Å.Â. Áàðáàçþê. -Áåðêóò. 14 (1). 2005. -Ðàáîòà ïðîâîäèëàñü âåñíîé è ëåòîì â 2000, 2001 è 2003 ãã. íà âîñòîêå Îðåíáóðã-ñêîé îáëàñòè, íà îçåðàõ Øàëêàð-Åãà-Êàðà (50°47. ø., 60°55. ä.) è Àéêå (50°58. ø., 61°30. ä.). Èñ-ïîëüçîâàëñÿ ìåòîä ïîëåâîãî ýêñïåðèìåíòà.  êàaeäîì îïûòå ïðîâîäèëîñü ïîýòàïíîå ïåðåäâèaeåíèå îäíî-ãî ãíåçäà ê áëèaeàéøåìó ñîñåäíåìó íåïîäâèaeíîìó. Îäèí îòðåçîê ïåðåäâèaeåíèÿ ñîñòàâëÿë 520 ñì. Ïîñ-ëå êàaeäîãî ïåðåäâèaeåíèÿ ïòèöàì ïåðåäâèãàåìîãî è íåïîäâèaeíîãî ãíåçä ïðåäîñòàâëÿëàñü âîçìîaeíîñòü âåðíóòüñÿ ê ãíåçäó è ïîñèäåòü íà íåì 1015 ìèí. Ïî îêîí÷àíèè îïûòà ãíåçäî âîçâðàùàëîñü íà ìåñòî. Ïðè ïðîâåäåíèè ýêñïåðèìåíòîâ, âî âðåìÿ êîòîðûõ ïîäîïûòíîå ãíåçäî ïîñòåïåííî ïåðåìåùàëîñü ê íå-ïîäâèaeíîìó ãíåçäó, õîçÿèí íåïîäâèaeíîãî ãíåçäà ïî-ðàçíîìó âîñïðèíèìàë ïîäîäâèãàåìîãî ñîñåäà, â çà-âèñèìîñòè îò ñòåïåíè óäàëåííîñòè ãíåçä äðóã îò äðóãà. Âûÿñíèëîñü, ÷òî ó ÷àéêîíîñûõ êðà÷åê ïðîñòðàí-ñòâî âîêðóã ãíåçäà ñîñòîèò èç òðåõ ýëåìåíòîâ, èëè ñóáúåäèíèö, íå âèäèìûõ ïóòåì îáû÷íûõ íàáëþäåíèé, íî õîðîøî ðàçëè÷àþùèõñÿ ìåaeäó ñîáîé ïî ñòåïåíè âûðàaeåííîñòè è ïðîÿâëåíèþ àãðåññèâíîñòè è ïî íà-ëè÷èþ èëè îòñóòñòâèþ íåêîòîðûõ ýëåìåíòîâ ïîâåäåíèÿ, íàáëþäàâøèõñÿ âî âðåìÿ îïûòîâ. ×àéêîíîñàÿ êðà÷êà äåìîíñòðèðóåò äîâîëüíî ñëîaeíóþ òåððèòîðèàëüíóþ ñòðóêòóðó, ýëåìåíòû êîòîðîé ìîãóò áûòü âû-ÿâëåíû òîëüêî ýêñïåðèìåíòàëüíûì ïóòåì.  íåé ïðîèñõîäèò íàðàñòàíèå àãðåññèâíîñòè êðà÷åê è óñèëå-íèå äèñêîìôîðòíîãî ïîâåäåíèÿ â íàïðàâëåíèè îò ïåðèôåðèè ê ãíåçäó ïî ñõåìå: ïîëíîå îòñóòñòâèå äèñ-êîìôîðòà, àãðåññèè → ïåðâûé ñëîé çîíû êîíôëèêòîâ → âòîðîé ñëîé çîíû êîíôëèêòîâ → àáñîëþòíî îõðàíÿåìàÿ çîíà.  àáñîëþòíî îõðàíÿåìîé çîíå àãðåññèâíîñòü êðà÷åê ìàêñèìàëüíà, ÷òî ïðîÿâëÿåòñÿ â èõ íåòåðïèìîñòè ê äðóãèì îñîáÿì. Àáñîëþòíî îõðàíÿåìàÿ çîíà ÿâëÿåòñÿ ñàìîé ñòàáèëüíîé åäèíèöåé òåððè-òîðèè è, âèäèìî, îáóñëîâëèâàåò íàëè÷èå äâóõ äðóãèõ òåððèòîðèàëüíûõ ñòðóêòóð ïåðâîãî è âòîðîãî ñëîÿ çîíû êîíôëèêòîâ, â êîòîðûõ êðà÷êà âûðàaeàåò ñâîå îòíîøåíèå, ñòåïåíü òåðïèìîñòè ê äðóãèì îñî-áÿì, íàõîäÿùèõñÿ íà ðàçíûõ ðàññòîÿíèÿõ îò åå ãíåçäà. Ïðåäïîëîaeèòåëüíî, àáñîëþòíî îõðàíÿåìàÿ çîíà ñîâïàäàåò ñ èíäèâèäóàëüíîé äèñòàíöèåé ïòèöû.
... Take-offs This phenomenon marks the pre-nesting period of Gull-billed Terns from appearance of the first birds at the breeding grounds up to the first week of egg-laying. On arrival terns get attached to a selected site (typically within a section of a sandy island) that initially serves as the club (Tinbergen, 1956) and roost, and afterwards as the breeding site. The pre-nest- ing period (from the arrival of the first birds at the breeding grounds to the clutch-initiation) lasts 16 to 38 days and possibly even more. ...
The phenomenon of synchronous takes-off displayed by Gull-billed Terns was studied during the pre-nesting period on Lakes Shalkar and Ayke, in southern Russia in 2000, 2003 and 2004. Synchronous take-offs of Gull-billed Terns are prominent phenomena observed during the pre-nesting period, and they could be considered as a component of pre-nesting aerial and ground behavior in this species. The intensity and dynamics of synchronous take-offs are influenced by a number of factors, among the more prominent ones being the time of the day, number of birds and weather conditions. The maximum number of synchronous take-offs was recorded in the morning and evening hours when the most birds were present at the gathering and roosting site. With the arrival of new parties of birds to the site the number of synchronous upflights increases, then reaches the maximum and stops rising when the mean number of birds is approximately 70 individuals per hour. The high intensity of synchronous take-offs is thought to be attributed to the abrupt change in the bird number per time unit, which occurs in the evening particularly from 19 00 to 20 30 . Air temperature and wind speed also have impacts on the intensity of synchronous take-offs, especially at their extreme values: strong wind in conjunction with low temperatures lowers the intensity of synchronous take-offs and vice versa. Synchronous take-offs are strongly suspected to be an adaptive mechanism permitting synchronous egg-laying and thus reducing overall duration of maximal reproductive stages, which is very important when nesting in unstable habitats. Ôåíîìåí ñèíõðîííûõ âçëåòîâ ó ÷àéêîíîñûõ êðà÷åê. -Å.Â. Áàðáàçþê. -Áåðêóò. 15 (1-2). 2006. -Ñèíõðîííûå âçëåòû ó ÷àéêîíîñûõ êðà÷åê ïðåäñòàâëÿþò ñîáîé ÿðêî âûðàaeåííîå ÿâëåíèå, íàáëþäàåìîå â ïðåäãíåçäîâîé ïåðèîä, è ìîãóò ðàññìàòðèâàòüñÿ êàê ÷àñòü áðà÷íîãî ïîâåäåíèÿ ýòîãî âèäà. Íà èíòåíñèâ-íîñòü è äèíàìèêó ñèíõðîííûõ âçëåòîâ âëèÿåò ðÿä ôàêòîðîâ, íàèáîëåå çàìåòíûìè èç êîòîðûõ ÿâëÿþòñÿ âðåìÿ ñóòîê, ÷èñëåííîñòü ïòèö, ó÷àñòâóþùèõ âî âçëåòàõ, è ïîãîäíûå óñëîâèÿ. Ìàêñèìàëüíûå çíà÷åíèÿ ñèíõðîííûõ âçëåòîâ íàáëþäàëèñü â óòðåííåå è âå÷åðíåå âðåìÿ, êîãäà íà ìåñòå íî÷åâêè ïðèñóòñòâîâàëà áîëüøàÿ ÷àñòü ïòèö. ×èñëî ñèíõðîííûõ âçëåòîâ óâåëè÷èâàåòñÿ ïî ìåðå ïðèáûòèÿ íîâûõ ïàðòèé ïòèö íà ìåñòî ïîñòîÿííîãî ñáîðà è íî÷åâêè, ñòàíîâèòñÿ ìàêñèìàëüíûì è ïåðåñòàåò ðàñòè ïðè ñðåäíåé ÷èñëåííî-ñòè ïðèìåðíî 70 ïòèö çà ÷àñ. Ïðåäïîëàãàåòñÿ, ÷òî âûñîêàÿ èíòåíñèâíîñòü ñèíõðîííûõ âçëåòîâ ñâÿçàíà ñ ðåçêèì ñêà÷êàìè ÷èñëåííîñòè ïòèö çà åäèíèöó âðåìåíè, ÷òî ïðîèñõîäèò â âå÷åðíåå âðåìÿ, îñîáåííî ñ 19 00 äî 20 30 . Òåìïåðàòóðà âîçäóõà è âåòåð ìîãóò òàêaeå îêàçûâàòü âëèÿíèå íà èíòåíñèâíîñòü ñèíõðîííûõ âçëåòîâ, îñîáåííî ñóùåñòâåííîå ïðè ñâîèõ ýêñòðåìàëüíûõ çíà÷åíèÿõ. Ñèëüíûé âåòåð â ñî÷åòàíèè ñ íèç-êèìè òåìïåðàòóðàìè ñíèaeàåò èíòåíñèâíîñòü âçëåòîâ è íàîáîðîò. Ïðåäïîëàãàåòñÿ, ÷òî ñèíõðîííûå âçëå-òû ÿâëÿþòñÿ ïðèñïîñîáèòåëüíûì ìåõàíèçìîì, ïîçâîëÿþùèì ñèíõðîíèçèðîâàòü ïðîöåññ îòêëàäêè ÿèö è ñîêðàòèòü òàêèì îáðàçîì ìàêñèìàëüíî ïðîöåññ ðàçìíîaeåíèÿ, ÷òî êðàéíå âàaeíî ïðè ãíåçäîâàíèè â íåñòà-áèëüíûõ áèîòîïàõ.
*** Barbazyuk, E.V. The phenomenon of synchronous take-offs in Gull-billed Terns // Беркут (Golden Eagle). 2006. V. 15, Issue 1/2. P. 159–175.
... However, this pattern has been mainly described in large white-headed gulls and explained by the frequent occurrence of cannibalism at a period when chicks are too young to defend themselves against territory intruders (Patterson 1965;Parsons 1971;Verbeek 1979;Watanuki 1988). In the small hooded-gulls, cannibalism seems absent or rare (Tinbergen 1956;Patterson 1965;Bukacinska and Bukacinski 1994) and a clear difference in aggression changes during the season from those observed in the larger gulls may be expected. An increase in adult aggression throughout the chick period has also been described in the Ring-billed Gull ( L. delawarensis ) and many factors have been suggested to explain it ( Southern and Southern 1982). ...
Although chicks of waterbirds usually stay in their nesting territory, in a few species they precociously leave the nesting site and join together in a “crèche”. While several authors have suggested a relationship between crèching behavior and reduced aggression in Larids, quantitative data on aggression in crèching species are missing. In this paper, we quantify the level of aggression through the breeding season in two evolutionarily independent species pairs, each consisting of two closely-related crèching and non-crèching species (Black-billed Gull, L. bulleri, crèching; Red-billed Gull, L. scopulinus, non-crèching; versus Slender-billed Gull, L. genei, crèching; and Black-headed Gull, L. ridibundus, non-crèching). Aggressiveness was similar among species until the chicks were 1-2 weeks old and then decreased in crèching species and increased in non-crèching ones. This change in aggressiveness at an age when chicks usually join a crèche strongly suggests it is related to crèching behavior. To broaden our study we suggest a comparative approach including Tern species.
... Although the evolution of coloniality has been intensively studied, the factors responsible for its evolution and maintenance are still subject of much discussion (see Danchin and Wagner, 1997 for a review). Coloniality is usually associated with several life history traits such as collective anti-predator behaviours (Wittenberger and Hunt, 1985; Siegel-Causey and Kharitonov, 1991), synchronisation of the breeding activities (Gochfeld, 1980) and a high frequency of aggressive interactions (Tinbergen, 1956, 1959). The formation of large groups of chicks in or near the colony site is one of the most intriguing traits associated with coloniality. ...
A crche is an aggregation of chicks outside nesting territories, within chicks continue to be fed only by their own parents. Several adaptive functions of crching have been proposed, the most frequent being a reduction in predator pressure. Using an evolutionary stable strategy approach based on the computation of individuals'' fecundity, we examined which regime of aerial and terrestrial predation is likely to favour the evolution and stability of the crching strategy (CS) in gulls. Our results confirm the hypothesis that habitat instability associated with high levels of terrestrial predation favours the evolution and maintenance of crching behaviour. Moreover, our results suggest that a low aggressiveness against predators may be a pre-adaptation to a CS. In contrast, the high synchronisation often observed in crching species does not favour the evolution of a crching behaviour and is thus probably under selection pressures different from those modelled here.
... Alternatively, the attacks may have been carried out by gulls moving into the study plots from adjacent areas where breeding had not been delayed. The majority of gulls in our study colony were unmarked and it was therefore not possible to determine if this was the case; however, this seems unlikely as gulls actively defend their breeding territories from other birds (Tinbergen, 1956;Burger, 1984). Moreover, the dierences between the gull-normal and gull-free plots suggest that there is little movement of gulls from the main breeding territories into the gull-free areas of the island. ...
Gulls frequently predate eggs and young and kleptoparasitise other seabirds during the breeding season. This has lead to the implementation of gull control programmes at many colonies. However, few studies have been carried out to assess the effectiveness of different management options. We investigated the impact of (1) maintaining gull-free areas and (2) delaying gull breeding, on the foraging economics and breeding success of puffins. Puffins breeding in gull-free habitat provisioned their chicks at a higher rate and had a lower risk of kleptoparasitism than puffins breeding in gull-occupied habitat. However, there was no significant difference between gull-free and gull-occupied habitat in puffin chick growth or survival. Delaying gull breeding by approximately 3 weeks had no impact on mean kleptoparasitism risk or the rate at which adult puffins provisioned their chicks. In line with these results, we found that delaying gull breeding had no impact on puffin chick growth or survival. Our results suggest that, under current conditions, gulls do not have an immediate negative impact on puffin reproductive performance.
Sexual differentiation of social behavior in gulls and its mechanisms remain unexplored beyond the breeding season. We described the development of aggressive territorial behavior in males and females of black-headed gulls at the age of 1–4 weeks, modeling the intrusion of a peer to the nesting territory. We also hypothesized that the sex differentiation of aggressive behavior may appear as a consequence of the development of small early differences between siblings in behavioral stress response. To test this assumption, we investigated the relationship between the priority among brood in aggressive contact with the intruder, and the within-broods level of activity of a chick to stress. To measure the behavioral stress response, we used the social isolation of chicks within a small water area with an island in the middle. Longer attempts to swim outside the fenced area were regarded as a more proactive stress response. At the age of up to 3 weeks, there were no sex differences in the aggressiveness, but the stress response of males was more proactive than that of their sisters, and a more proactive chick in the brood was usually the first to attack the intruder. At the fourth week of life, the aggressiveness of males increased significantly, and in broods of two sexes, brothers began to play a leading role in protecting the nesting territory in the absence of parents. They attacked the intruder more often and made aggressive calls more frequently. Thus, we were the first to reveal sexual differentiation of territorial behavior in gull chicks in the pre-fledging period. Our results suggest that under natural conditions, where the intruder does not persist in staying in the other nest, but recedes immediately when counteracted, more proactive males use to attack the intruder earlier than sisters do. As a result, they gain experience of aggressive interactions, and develop higher abilities of aggressive responses to social challenges.
The problem of adaptive significance of territorial antagonism in colonial birds is addressed. Many of these birds are characterized, along with high tolerance to each other and tendency to aggregate, by intensive and variable territorial demonstrations. Here we consider the effects of territorial behavior on the viability of a breeding colony. We observed breeding of black-headed gull in two colonies formed under the impact of a short-term temperature fall in 2008, which resulted in the 7-day shift in timing of egg laying. Compared with the colonies at the same places, one in 2007 and one in 2009, in 2008 the number of nests and their density were rather smaller, whereas the duration of settling, the nest density increase and the average size of breeding territories have not changed. Average body weight of adult birds during incubation was stable through all the years. However, correlations, typical for 2007 and 2009 (negative between female mass and date of clutch starting, and positive between masses of parents), were absent, suggesting that assortative mating by body mass and territory size was not the case in 2008. Average clutch, egg, and hatchling sizes were smaller in 2008 while mortality due to aerial predators was higher than in normal years. In 2007 and 2009, birds who started egg laying in the first 5 days after the first egg appeared in the colony (settlers) were larger than others (so-called followers) and produced larger offspring. These differences were not observed in 2008. According to our data, after the impact of cold weather, some birds abandoned their nesting sites, others were sick but mostly behaved as settlers and formed underpopulated and sparse colonies. We assume that the formation of a viable colony requires interaction of highly territorial 'pioneers' and a certain number of less competitive individuals. Withdrawal of the latter results into a general reproductive failure of the colony. Thus, the pattern of colony formation as in the black-headed gull turns natural selection towards maintenance of the variety of individual programs of territorial competition.
Přírodovědecká fakulta Jihočeské univerzity, Branišovská 3, 370 05 České Budějovice; Frantová D. 2007: Kopulační aktivita racka chechtavého (Larus ridibundus). Sylvia 43: 51–60. Kopulační aktivita racka chechtavého (Larus ridibundus) byla sledována v hnízdní kolonii, která se nachází na 9 ostrůvcích rybníka Domin u Českých Budějovic. Racek chechtavý je mo-nogamní, koloniálně žijící pták. Jedná se o druh, kde oba partneři silně investují do rodičovské péče a kde rozchod není výhodný ani pro jednoho člena páru, protože snižuje jejich vyhlídky na rozmnožování v příštím hnízdním období. Celkem bylo pozorováno 473 kopulačních po-kusů, převážnou většinu z nich (98 %) tvořily nevynucené kopulační pokusy. Vynucené kopu-lační pokusy (2 %) nejsou u tohoto druhu běžné a zřejmě nepředstavují strategii samců vedou-cí ke zvýšení počtu potomků. Dlouhodobá párová vazba racka chechtavého je spojena s vyšším reprodukčním úspěchem – je-li pár obnovován po více sezón jeho reprodukční úspěch se zvyšuje. Věrnost partnerů a posilování párové vazby je zřejmě v reprodukčním systému racka chechtavého výhodnější než vyhledávání mimopárových kopulací. Copulation activity of the Blackheaded Gull (Larus ridibundus) was observed in a breeding colony located on 19 islands in the fishpond Domin, České Budějovice, Czech Republic. In total, 4713 copulation attempts were observed. The majority of attempts (98%) were unforced ("pair") copulation attempts (PCA). Forced copulation attempts (FCA) are not frequent (2%) in this monogamous species and forced copulations (FC) do not seem to be the main male strategy for increasing the number of their offspring. In the Blackheaded Gull the longterm pairbonds are associated with increased reproductive success and the longer pairs remain together, the greater is their reproductive success. In such a mating system, mutual mate fidelity and strengthening the pairbond seem to be more advantageous than seeking extrapair copulations.
Laughing gulls Larus atricilla, nesting in saltmarshes subject to tidal inundations, build substantial nests and continue adding material throughout the reproductive cycle. Under normal conditions, nest size increased until gulls had 5-day-old chicks. I manipulated nests at various stages in the reproductive cycle. Until their chicks reached 14 days of age, gulls added material to artificially wetted nests, making them significantly deeper and wider than before treatment. During all reproductive stages examined, gulls repaired nests having half of the material removed. The adaptive significances of nest building and relative nest size are discussed in terms of washouts and the requirements of the eggs and chicks at different stages in the reproductive cycle.
Incubating herring gulls, Larus argentatus, quickly learned to operate feeding boxes placed on their territories. Subsequently, they were rarely observed to be absent from their territories and their nest-relief behaviour and incubation schedules differed significantly from that of a control group. Mates in the control group apparently adopted complementary feeding strategies and the relative abundance of an individual's preferred foods was correlated with its nest-relief behaviour.
Black-headed Gulls at Ravenglass (Cumbria) show a marked preference for nesting in the cover of marram, which is however replaced by nettles after several years of fertilisation of the dunes by the birds' guano. The marram recovers some years after desertion of nettle areas, and shifts within the gullery are always from nettle-grown to new marram sites.
Yellow-legged gulls breed in high density areas, and the conditiondependent hypothesis suggests that birds with high physical condition can obtain breeding benefits in high-density areas because they are able to pay off the energetic costs of aggressive behaviour and territory defence. This study and others showed a relationship between aggressiveness or copulation behaviour and nest-density during the pre-laying period in gulls. The link between density and behaviour can be explained by the strong competition for space and mates. Testosterone regulates male behaviour and can play an important role in the condition-dependent hypothesis. We tested the effects of testosterone implants on male breeding behaviour. In a high-density colony, testosterone-implanted male yellow-legged gulls showed higher aggression and copulation frequencies than controls during the courtship period. In addition, these testosterone-treated birds acquired larger territories than the controls. Thus, a high testosterone level can increase individual fitness in densely populated areas given the benefits derived, on the one hand, from a large territory and, on the other, from an increased copulation rate that would guarantee the male's paternity of the chicks born in his own nest. Since testosterone increases energetic requirements, only high-quality males would be able to pay off the costs of high levels of testosterone and so obtain the benefits of breeding in high-density areas. Testosterone could therefore provide a proximate mechanism regulating nest density in gull colonies.
The relationship between nesting density and breeding success of Herring Gulls Larus argentatus was studied on the Isle of May, Scotland, in 1968. Herring Gulls nesting at the most common density started laying earlier in the season than those nesting at lower or higher densities. Therefore, although the overall spacing of nests was uniform, the nest density of birds laying later in the season progressively approached a random distribution. The onset of laying occurred in synchronized groups within the colony. Late-laid clutches were commonly situated on the periphery of the colony where the density of nests was lowest. When the laying period was divided into four time periods, in each period the tendancy was for birds nesting at the most common density to have the highest clutch-size, hatching and fledging success, and to rear the most chicks per pair to fledging. In addition, birds which spaced their nests most uniformly, presumably as a consequence of territorial behaviour, were the most successful parents.
Kelp Gulls nested in six colonies on rocky islands, sand and rock cliffs, sand dunes and on a sand, gravel island in a salt lake. The colony sites selected were different from the surrounding areas and were generally inaccessible to ground predators. Kelp Gulls nested in a wide variety of habitats. Within colonies, the gulls did not nest randomly with respect to habitats but preferred to nest on flat, stable areas with some cover (either rocks or vegetation). They generally avoided heavily vegetated areas, areas devoid of vegetation and areas with steep slopes. Their specific habitat choices relate to predation and cannibalism pressures. Intermediate cover provides adequate protection for chicks while allowing for increased visibility and open escape routes for parents. Nearest neighbour distances were similar among colonies and habitats, indicating strong social attraction.
We examined the pattern of colony occupation and egg-laying in five colonies of Herring Gulls nesting in New Jersey, U.S.A. Colonies formed from epicentres located in sparse bushes. The number of epicentres related to the number of birds nesting in the colonies. Colonies of over 250 pairs had more than one epicentre, whereas those with under 250 pairs had only one epicentre. Epicentres were not always in the geographical centre of the colonies. New territory-hunting pairs filled in the epicentre areas, and then nested outside these areas. The egg-laying pattern followed the settling pattern, but was more synchronous than the settling pattern. There was greater synchrony of egg-laying within sub-areas of the colonies than in the colonies as a whole. Further, synchrony correlated with the number of nests in sub-areas.
Common Terns nested on 34 of 259 saltmarsh islands along 46 miles of Ocean County coastline, New Jersey. They nested on low islands of Spartina with less than 12%, windrow ranging in size from 0.6 to 108 acres. All islands selected by terns faced at least two miles of open water from at least one direction. Selection of islands seemed a response to vegetation, size, distance to the nearest island, distance to the nearest shore and exposure to open water. Of the 225 islands without nesting terns, only three fulfilled appropriate criteria.
Eighty per cent of nests were situated on windrow. Terns laid larger clutches on windrow compated to those nesting in Spartina . Nearest neighbour distance on islands with low predation varied from 85 to 485 cm and was a function of space, vegetation, and the size of the island. Terns nested closer together on windrow compared with Spartina . Considering all colonies, the mean nearest neighbour distance negatively correlated with the number of nests.
Skimmers, Oystercatchers, Laughing Gulls, and Herring Gulls nested in some of the tern colonies. All tern colonies on islands also occupied by nesting Herring Gulls suffered over 10% egg‐loss by predation. Proportionally more nests were preyed upon in windrow than in Spartina . Clutch sizes in nests in windrow on islands with predation were significantly lower than those in windrow on islands without predation, even though clutch sizes in Spartina were similar on islands with and without predation.
Flooding by exceptional high tides destroyed significantly more nests in Spartina than in windrow. The nests that survived in Spartina were built deeper, and their rim heights were higher than nests destroyed by tides.
Choice of colony and nest sites is discussed in terms of the balance of two selection pressures: predation and tidal flooding. Tern nests on windrow are more exposed to predators, but safer from flooding, whereas those nests in Spartina are more susceptible to flooding and less vulnerable to predators. The recent invasion of Herring Gulls into Ocean County has significantly increased the rate of nest predation among affected colonies of Common Terns. It is possible that in future years the terns' behaviour may be modified in response to this new selective pressure.
Seasonal and diurnal changes in territory size and frequency of aggressive interactions of various intensity were examined in colonies of the black-headed gull (Larus ridibundus) on river islands and ponds of central Poland. The highest frequency of the total aggression and the largest territories were recorded before the egg-laying stage, this being related to the establishing of territories, defence of the mate, and defence of nest material. Later in the season both aggression and territory size declined. Unlike the large species of gulls, black-headed gulls did not increase their aggression and territory size during hatching of the young. High-intensity aggressive behaviours (choking, attacking and fighting) were not so frequently displayed as low-intensity aggressive postures (upright, long call, forward) in each phase of the breeding cycle. Presumably this was because the former were more costly in terms of energy. Peak territorial activity occurred in the late afternoon. An increase in the frequency of intense aggressive behaviours (attack, fight) at that time was combined with an increased mobility of birds (departures to and arrivals from foraging sites). A reduced frequency of high-intensity aggressive displays in the period when the largest number of birds was present in the colony was likely to be adaptive.
The nesting habitats adopted by most colonies of Black‐billed Gulls Larus bulleri are river‐beds that are subject to flooding.
A number of respects in which the reproductive behaviour of Black‐billed Gulls differs from that of at least most other gulls, such as Black‐headed Gulls, can be viewed as adaptations, or byproducts of adaptations, to such nesting habitats:—
A different breeding site from the year before is often selected
The bulk of pair formation is accomplished before the gulls occupy their breeding sites; nesting territories are set up by mated pairs
In hostile encounters during the pair formation phase, site attachments are weak or transitory
In agonistic situations generally, attack thresholds appear to be relatively high, and fleeing thresholds relatively low
High intensity forms of“Choking” appear to be missing from the agonistic display repertoire
The growth of nest groups is rapid and orderly; nesting territories are small and the concentration of nests in the groups high
The time between occupation of the gullery site and the start of laying is short, and the synchrony of laying is high; this is probably related to the close proximity of the nests
The parents and young abandon the nest very soon after the egg hatch, and no “brood” nests are made
The young may develop locomotory powers more quickly than is the case in most other species; they can swim at an early age, and take to the water in tightly packed groups during alarms
The question of why these gulls should choose such vulnerable breeding sites is discussed.
Prior to the present study, no systematic field data were available on the behaviour and ecology of Erythrocebus patas. This monkey, widely distributed over the grass and woodland savannah regions of West and East Africa, appears to be unique in some of its physical and social adaptations to a terrestrial mode of life. In three main study periods, 640 hours of observation were carried out on groups in the Murchison Falls National Park. Small samples of data on baboon and vervet groups in the same area were obtained. Numerical sizes of patas groups ranged from 9 to 31, mean 15. In no group was there more than one full‐grown male. Groups were followed for many successive day‐ranges, distances travelled varying from group to group, season to season, with a maximum of about 12,000 m and a minimum of 500 m. Home range size of one group was 5200 hectares. Groups tended to use a different area of the home range each night, and individuals dispersed far apart in taking up night resting positions in trees. The day activity pattern comprised two main feeding periods, with a rest period of one to three hours in the hottest time. Drinking at water holes or other sources was infrequent.
Infants less than three months old occurred only up to June, and were commonly seen in March and April. Infants aged 3 to 12 months, and juveniles, engage frequently in long, active bouts of play‐chasing, wrestling, and bush‐bouncing–almost all play is on the ground. Grooming amongst them is common, its social pattern being similar to baboons. Submissive gestures are very rarely seen, baboon‐like presenting and being mounted not occurring. Threat‐attack is mainly by adult females, very rarely by the adult male. Vocalizations audible at about 100 m occur very infrequently (about two to four a day, compared with 25 to 50 for baboon groups).
The adult male patas plays the part, for the group, of watchdog. Whenever the group is disturbed, or approaches new areas, he may reconnoitre from a high point several hundred metres away from the group. When disturbed by the observer, he has a noisy, bouncing display on bushes and trees, and probably a form of diversionary display by running away from his group and from the observer. In the group, he is spatially peripheral, except when day resting, mating and grooming, and the adult females habitually initiate directions and times of group movement. Their function is essentially that of looking after themselves, their infants, and the juveniles, while that of the adult male is very strikingly that of watching for predators or other patas groups or baboons, etc. Isolated adult males and one all‐male party of four have been observed. Spacing between groups is such that inter‐group encounters are exceedingly rare (two occurrences only). Reaction consisted of chasing by the larger group, rapid avoidance by the smaller. A contralto bark is uttered repeatedly, in short series, by the adult male of a group only, it seems, on encounters with extra‐group patas.
The patas adaptations of swift locomotion, silence, concealment, and dispersal, contrast very clearly with those of the much noisier, larger, more aggressive baboons in whose groups there are usually several adult males.
Further research on the species is required from West Africa, and captivity studies must be used to determine the precise nature of the social organization amongst the adults and the processes of socialization.
Various aspects of territoriality were studied comparatively in a marked population of Reed and Sedge warblers at the Attenborough Nature Reserve, Nottinghamshire. Differences in arrival patterns, establishment of territory and particularly territory size were detected. In view of the dynamic nature of territory boundaries, a method is described for obtaining measures of mean territory size for comparative purposes. The sympatric species were largely separated by different breeding and feeding habitats, but there was also a degree of interspecific competition in some areas and interspecific territorialism was found to occur. Adults of both these migratory species were found to exhibit strong site fidelity, and there was some evidence to suggest that early post-fledging experience may influence initial selection of a particular area and territory for first breeding.
The adaptive significance of territory is discussed in relation to the findings presented and current hypotheses. There was some evidence which suggests that reduction of predation pressure and intraspecific interference through spacing out, as well as provision of a nest-site may be important functions of territory in these species, but no evidence that food supply or population regulation are involved. The significance of interspecific territorialism is considered in relation to interspecific competition. The various factors effecting territory size and the patterns of nesting dispersion are also considered in an attempt to account for the striking interspecific differences found between these closely related species. It is concluded that although a multiplicity of factors may well be interacting in complex fashion, the more important of these stem from contrasts in the physical properties of the two habitats.
This paper forms an introduction to a symposium on the territorial behaviour of birds.
Following Noble (1939), territory is defined as “any defended area”. A simple classification of breeding territories is given, and the diversity of territorial behaviour emphasized.
Territorial behaviour can be analysed into at least two components—restriction of some or all types of behaviour to a particular area, and defence of that area. These are often accompanied by self‐advertisement.
The aggressive behaviour which arises in different situations depends primarily on the same mechanisms, though the fighting may be specialized to serve different functions (e.g. to defend different objects). This justifies the broad definition of territory given above.
The fighting involved in territorial defence is associated with tendencies both to attack and to flee from the rival.
The nature of the evidence concerning the biological functions of territorial behaviour is considered. In previous discussions of this subject the term “function” has sometimes been used to refer to any advantageous consequence of the behaviour, and sometimes restricted to consequences through which selection in favour of the behaviour can act.
Various possible functions of territory are considered.
Circumstantial evidence suggests that the familiarity with the area which results from site attachment may assist feeding, escape from predators, etc., and may also increase fighting potentiality.
There is strong evidence that territorial behaviour, in addition to producing over‐dispersion, can regulate density in favoured habitats. There is no direct evidence that territory limits the total breeding population in all habitats.
In many species, it facilitates the formation and maintenance of the pair‐bond.
It may also reduce interference in various reproductive activities by other members of the species.
Defence of the nest‐site is an important consequence of territorial behaviour in many species, and the aggressive behaviour is often clearly specialized to this end.
In a few species territory is primarily concerned with food, but in most the food value of the territory is not significant. Even in the species which feed on their territories, the territorial behaviour is not specialized for the defence of food objects:in these cases it is possible, but unproven, that the territorial behaviour does help to ensure an adequate supply of food for the young.
In some species the over‐dispersion produced by territorial behaviour may reduce predation, though direct evidence that this is the case is not available.
Maintenance of a territory may reduce the despotism of other males, but this does not explain the function of territorial aggressiveness.
Territorial behaviour may reduce disease, but this is unlikely to be a significant consequence except in some colonial species.
It is unlikely that the prevention of inbreeding and the promotion of range extension are significant consequences of territorial behaviour.
The functions of territorial behaviour are extremely diverse, and the quality of the evidence available for assessing them is little different from that available to Howard. Since territorial behaviour has consequences both harmful and advantageous to the individual's chances of ultimate reproductive success, and since the inter relations between the selective forces governing behaviour, structure and physiology are extremely complex, simple answers about the function of territory cannot be expected.
In this study we assessed territory turnover of the European Scops Owl Otus scops, a migratory nocturnal raptor, using sonagrams of hoots recorded in the same territories in the 1993 and 1994 breeding seasons. Three structural parameters of the hoot (duration, inter-note interval and frequency) varied considerably, and a Discriminant Function Analysis classified >90% of individual calls correctly. In order to investigate yearly turnover and site-fidelity of male Scops Owls, the discriminant functions derived from the hoot sample recorded in 1993 were used to classify hoots of individuals recorded in the same territories in 1994. Apparently, turnover rate of territory owners was high and rapid, because 55–78% of territories censused in 1993 were defended by a different male in 1994. The fast decline of our Scops Owl population, probably due to winter mortality, could be responsible for such a high turnover of territorial owners.
Functional hypotheses about animal signalling often refer to mental states of the sender or the receiver. Mental states are
functional categorizations of neurophysiological states. Functional questions about animal signals are intertwined with causal
questions. This interrelationship is illustrated in regard to avian distraction displays. In purposive signalling, the sender
has a goal of influencing the behavior of the receiver. Purposive signalling is innovative if the sender's goal is unrelated
to the biological function of the signal. This may be the case in some instances of false alarm calling. Biological functionalism
differs from philosophical functionalism in its concept of identity and in the specification of relevant inputs and outputs.
The behaviour and ecology of Franklin's gull were studied at Agassiz National Wildlife Refuge in northwestern Minnesota to determine the adaptations of the species for nesting in marshes. Two factors seemed to be important in colony site selection: cattail dispersion pattern and cattail density. Franklin's gulls prefer to nest in cattail areas closest to open water. The number of nests per unit area decreased as cattail density increased. Nest site selection is dependent on aggression and visibility. Visibility from nest level is the result of cattail placement and height. The distance between nests was directly correlated with visibility. Aggression by gulls on nests was lowered experimentally by decreasing visibility and raised by increasing visibility. Nest platforms were constructed of cattail material, and were attached to cattail stems. Nest material was added to the nests throughout the incubation and brooding period. Material was usually added following nest relief. The egg laying period was from 6 to 28 May. There was more synchrony of egg laying in sub-areas of the colony than in the colony as a whole. Successive eggs in clutches were laid at 24- to 48-hr intervals. The distance between nests decreased during the season as pairs filled in areas that were not defended. Territorial pairs defended an area up to 10 m from their stations prior to egg laying, but defended only the area within 3 m of their nests during incubation. Both members of pairs incubated the eggs and cared for the young. The incubation period was 24 days. The primary predators on adults and young were marsh hawk, great horned owl and mink. Franklin's gulls do not eat eggs or young of gulls. Adults fed on earthworms, insects and grain. Most marked adults fed within 16 km of the colony. Chicks were fed primarily on earthworms. The hatching period was from 30 May to 21 June. Chicks of all ages tested on a visual cliff apparatus were able to perceive the drop. Chicks tested on a 30-degree incline apparatus walked up it when 6 days old and younger, and walked down at 12 days of age and older. Brood mobility was less than in ground nesting species of gulls. In an undisturbed colony the chicks remained on the nest platforms until they were 25 to 30 days old although they were capable of swimming shortly after hatching. Individual recognition between parents and chicks appeared later in this species than in ground-nesting gulls. Adults accepted alien chicks (experimentally exchanged) that were younger than about 14 days old until their own chicks were over that age. Adults accepted larger and older broods than their own, as well as broods of mixed ages. Chicks began to react differently to strange adults at about 16 days of age. The breeding chronology of Franklin's gull is compressed when compared to that of other gulls. Possible selection pressures affecting this synchrony are discussed. The behaviour of the marsh-nesting Franklin's gull is compared with that of typical ground-and cliffnesting gulls; the possibility that the ancestral gull may have been a marsh nester is discussed.
The nest-relief behaviour of herring gulls Larus argentatus can be classified in terms of the apparent relative willingness of mates to undertake incubation duties. In this paper the nest-relief behaviour is described and its occurrence correlated with the availability of foraging opportunities. It appears that a conflict of interest arises when feeding opportunities occur, and that this is reflected in the nest-relief behaviour.
Experiments were made to find out whether caterpillars of Ennomos alniaria, Biston strataria and B. hirtaria are protected from Jays and Chaffinches by their resemblance to sticks. Being used to the inedibility of sticks, the birds do not peck at the larvae. However, once it has found one by accident, a bird will usually peck at all similar objects until it is discouraged by finding only sticks. The original situation is then restored. The caterpillars are confused only with sticks of their own food plants, and some birds are able to distinguish them even from these. Even in its present highly refined form, therefore, the adaptation does not yet give the maximum possible protection, and all steps in its evolution will have had a considerable selective advantage.
In preparation. A reconsideration of the problem of “territory” Bird Study
- N Tinbergen
Möwenbeobachtungen in Basel
- Burckhahdt D.
Zur Ethologie bzw. Psychologie der Silbermöwe, Larus a. argentatus Pont
- Portielje A. F. J.
De schutkleur der takspanners
- Tinbergen N.
Bosvogels en insecten
- Tinbergen L.
Das Verhalten der männlichen und weiblichen Silbermöwen (Larus a. argentatus Pont.) ausserhalb der Brutzeit
- Drost R.