Breeding Performance

(To be updated)

Studies of breeding performance

During the first years of the studies on Greylag Geese in Scania breeding performance was intensively studied in the four main lakes of the study area. From 2001 onwards the work on these aspects have not been so intensive. Due to changes in the breeding areas only Lake Yddingen and Klosterviken were sutiable for this kind of work, and observations were koncentrated here. The aim of observations in later years have been to follow the breeding performance in these two lakes and also to study longterm changes in the breeding performance in relation to the development of the breeding populations.

This page informs on the results of the early studies. Later observations have not yet been analyzed but the results will be presented here later.

Overall brood size and breeding success

The majority of the Greylag Geese breed in reed beds, making regular nest controls unfeasible. Most data on the breeding performance thus refer to the observations of pairs with small young or with fledged young. Especially the production of fledged young can be established for a very high percentage of all marked pairs as the geese gather in a few large flocks when the young are capable of flying.

Island breeding pairs in Lake Yddingen and Fjällfotasjön have in some cases made it possible to establish the number of eggs and later the production of small and fledged young. Greylags from Lake Yddingen with much better feeding conditions at the golf course than the Greylags at   Lake Fjällfotasjön had a higher clutch sixe and and initial brood size than the geese from Lake Fjällfotasjön. Moreover the survival to fledging (and even later) was much better for the young from the lake with the better feeding conditions. The differences between the other lakes were not so marked.

Choice of breeding lake

The variation in brood sizes between the different lakes  indicate that there are marked differences in breeding performance relating to the choice of breeding lake. Especially Lake Yddingen was found to have much larger brood sizes both for small and fledged young than the other lakes. The young at Lake Yddingen were significantly heavier at marking than the young from the other lakes, this being an indication of better feeding conditions at Lake Yddingen than at the other lakes.

Effect of winter area on future breeding performance

The Greylag Geese from Scania wintering in the Marismas in south-western Spain in general had a lower success rate (i.e. producing at least one fledged young) than the geese wintering in the Delta area of the Southwest Netherlands. Overall 48% (N=482) of those wintering in the Marismas were successful compared to 55% (N=251) for those wintering in Holland. The difference was very marked in some years, and could be related to shifting habitat condition in the Marismas. Thus there was a significant correlation between the rainfall in the winter quarters (and thus habitat conditions) and the proportion of pairs from this wintering area producing a brood of fledged young. For those managing to produce a brood there were no differences in mean brood size between the two winter areas. 

There was also an effect of the staging habits during the migration between the Marismas and south Sweden on the breeding performance. Greylag Geese wintering in the Marismas and staging in Villafafila in northern Spain were significantly more successful than those not staging there or those staging in France during spring migration (pairs not suffering from partner death due to hunting). In the Dutch Delta, the proportion of successful pairs increased markedly after the introduction of a hunting ban in the most important reserve, minimising disturbance. Moreover, early arriving geese were more successful than late arriving.

Experience of the parents was another factor of importance for the breeding result.  For all lakes except Fjällfotasjön new breeders had an appreciably smaller brood size at fledging than experienced breeders. Besides experience there was also an age effect, the success rate increasing up to the age of four even for geese starting to breed at the unusual age of two years.

Social factors are also important for the breeding success. Thus there was a clear increase in the size of broods with the length of the pair bond up to four years (of known history) with the same partner. Co-operation between the partners of a pair is another factor of importance. The death of a partner for some reason leads to a markedly smaller brood size of both small and fledged young for the surviving partner in a new relationship the following breeding season. In a number of cases, a separation and repairing was observed with the two former partners still alive and breeding in the same area. Divorcing pairs had a much lower mean brood size before the divorce than the population mean.

The experience and age of the marked breeder have been noted as  important factors behind much of the variation in the breeding result of Greylag Geese. Even if the time period for the present study is too short for a study of life-time reproductive success, it is clear that there are very marked differences in the productivity of different individuals when measured as the number of fledglings.

The majority of marked Greylag Geese followed for a number of breeding seasons did only produce a few fledged young. For geese followed during five breeding seasons 4 of 42 managed to get more than 20 fledged young. The "top" individual in our sample was a male followed for 12 years, producing 37 fledged young.